Lithium is a promising anode material for next-generation high-energy-density rechargeable batteries owing to its high specific capacity, low density, and low electrochemical reduction potential. However, dendrite growth during cycling impedes its practical application and causes safety hazards. Extensive research has been conducted to obtain dendrite-free safe Li anodes with an extended cycle life by electrolyte or anode surface modification. In previous studies, the symmetrical Li/Li cell test was widely applied to evaluate the effect of various Li anode modification methods on the cycle stability and Li deposition overpotential. However, a general criterion has not yet been established to identify the short circuit in Li/Li cells. Some researchers have even made incorrect conclusions based on the Li/Li cycling data. The most common misjudgment is the ignorance of short circuit signals and mixing up of soft short circuit and normal potential decrease caused by electrode activation. In some studies, the fractal voltage signals were attributed to the unstable activation process of the symmetrical cell. Therefore, this study uses an in situ optical cell to demonstrate that a short circuit caused by the contact of dendrites from two opposite electrodes can cause a sudden drop in cell voltage to certain extent. According to the reversibility of the voltage, the short circuit induced by dendrite growth can be classified into unrecoverable hard short circuits and recoverable soft short circuits. Typical short circuit data were summarized and described to establish a rule to determine the different types of short circuits. The voltage profiles provide characteristic signals to distinguish between the soft short circuit, hard short circuit, and cell activation processes in symmetrical cells. Furthermore, this study provides a reference for identifying dendrite growth and cell short circuits, which is important for confirming the practical effect of different modification methods.

The growing demand for electric vehicles, communication devices, and grid-scale energy storage systems urgently calls for the development of rechargeable batteries. Although lithium-ion batteries have dominated the new energy market for decades, there are challenges limiting their development, such as the high cost of lithium, as well as the toxicity and flammability of the organic electrolyte. In recent years, aqueous zinc-ion batteries (ZIBs) have gained much attention due to their advantages of high safety, high capacity, low cost, and nontoxicity. Materials based on multivalent vanadium and manganese have shown great potential for application as cathodes that are compatible with the metallic zinc anode in ZIBs. However, the commercialization of ZIBs has been hindered by the choice of cathodes, since the cathode materials show unsatisfactory energy densities and suffer from severe structural collapse, dissolution of the electrode components, sluggish reaction kinetics and detrimental side reactions during cycling. This stalemate was broken when a Zn²⁺/H₂O co-inserted V₂O₅ (Zn_0.25V₂O₅·nH₂O) material was first reported in 2016, and it showed much higher cycling stability and capacity than those of V₂O₅. The Zn²⁺ and water molecules pre-intercalated into the interlayer served as pillars to maintain the crystal structure and increase the interplanar spacing, leading to high structural stability and fast Zn²⁺ diffusion. Since then, several guest ions (Li⁺, Na⁺, K⁺, Ca²⁺, NH₄⁺, PO₄^3-, N^3-, etc.) and molecules (H₂O, polyethylene dioxythiophene (PEDOT), polyaniline (PANI, etc.) have been widely used to improve the electrochemical performance of aqueous ZIB cathodes, especially with manganese-based and vanadium-based materials. It is demonstrated that pre-intercalation of the guest ions or molecules can effectively optimize the electronic structure, regulate the interplanar spacing, and improve the reaction kinetics of the host. The local coordination structure of the host with pre-intercalated guest ions/molecules directly influences the zinc-ion storage performance. For example, sodium vanadates with a tunneled structure generally show better cycling stability than those with a layered structure due to their stronger Na-O bonds, since the O atoms on their layer surfaces are only single-connected. Manganese dissolution could be greatly suppressed by intercalation of the large potassium ions into tunneled α-MnO₂, where solid K-O bonds act as pillars to be connected with Mn polyhedrons, and thus strengthen the structure. New mechanisms underlying reduction/displacement reactions could also be revealed in vanadates upon the introduction of Ag⁺ and Cu²⁺. Thus, we believe that guest pre-intercalation is a promising method for optimizing the zinc-ion storage performance of the appropriate cathodes and is worthy for further exploration. Here we have reviewed the recent advances in manganese-based and vanadium-based cathodes via the guest pre-intercalation strategy, discussed the related advantages and challenges. The future research direction for these two kinds of aqueous ZIB cathodes is also prospected.

Hydrogen oxygen fuel cells and water electrolysis serves as two important systems for realizing the recycling of hydrogen energy, which involves two crucial electrochemical reactions, the hydrogen oxidation reaction (HOR) and the hydrogen evolution reaction (HER). The kinetics of HOR/HER in alkaline media is 2 or 3 orders of magnitude slower than that in acidic media, which is the main bottleneck that hinders the development of alkaline membrane fuel cells and alkaline water electrolysis. Thus, clarifying the underlying difference of HOR/HER activity in alkaline and acid electrolytes, and exploring the alkaline HOR/HER mechanism are the significant challenges for widely commercial application of low temperature alkaline energy conversion devices. Here, this paper briefly reviews the related explanations and controversies about the alkaline HOR/HER mechanism in recent years, including bifunctional mechanism, hydrogen binding energy (HBE) theory and electronic effect. The bifunctional mechanism emphasizes the influence of water dissociation and OH adsorption on HER and HOR, respectively, which possesses guiding significance for designing and fabricating composite catalysts. The HBE theory stresses that H_ad is the key reaction intermediate of HOR/HER, and other external factors, such as electrode potential, pH, ions and so on, affect the HOR/HER mechanism and kinetics by disturbing HBE. HBE is widely considered to be the only activity descriptor of HOR/HER. The electronic effect emphasizes the role of catalysts' composition and reaction intermediates in regulating electronic structure of active sites and changing HOR/HER mechanism. It provides an effective strategy to construct active sites and optimize catalytic activity. In addition, we summarize the theoretical simulation methods of electrochemical interface and their applications in exploring HOR/HER mechanism. In-depth theoretical simulation of HOR/HER mechanism requires the establishment of a more reasonable explicit solvation model on electrode/electrolyte interface and the combination of density functional theory (DFT), ab initio molecular dynamics (AIMD), and microkinetic model, to calculate the electronic structure and the dynamic processes of electrode/electrolyte interface, such as bond breaking and formation, solvent recombination, and proton migration in the electric double layer during reaction process, and then to analyze the HOR/HER mechanism and reaction kinetics under different electrode potentials and electrolytes. The present review is helpful for understanding the ongoing developments of HOR/HER mechanism. And the combination of experiment and theoretical calculation can be employed to explore the pH-dependence of HOR/HER deeply, and design novel HOR/HER catalysts with high activity and stability.

Semitransparent organic solar cells (ST-OSCs) have attracted attention for use in building integrated photovoltaics because of their large range tunability in colors, transparency, and high efficiency. However, the development of semitransparent devices based on fullerene acceptors remained almost stagnant in the early period. This was due to the weak absorption of fullerene small molecules in the visible and near-infrared regions as well as the large non-radiative energy loss, resulting in drastic open-circuit voltage loss. In addition, the energy level and chemical structure of fullerene molecules cannot be easily regulated, and the strong aggregation characteristics of fullerenes greatly limit the development of OSCs. In contrast, the designability of the chemical structures and controllability of the energy levels of non-fullerene electron acceptors has encouraged researchers to explore high-performance organic solar cells while and simultaneously stimulating the development of ST-OSCs. In this review, the recent progress in non-fullerene small molecule acceptors for ST-OSCs is summarized. The article focuses on ST-OSCs from the aspects of device structures and active layers. In view of the semitransparent device structure, except for replacing the traditional electrodes with semitransparent electrodes, researchers have introduced suitable interface layers to regulate the absorption and reflection of sunlight. The interface layers mainly contain a reflective layer (evaporated on the top electrode to reflect near-infrared light); an anti-reflection layer (located below ITO (indium tin oxide)) to mitigate light reflection at the air-glass interface and thus enhance the absorption of sunlight); and an optical outcoupling layer (simultaneously increasing reflection and transmission). From the active layer, it is mainly divided into two categories. First, researchers have optimized the photovoltaic performance of semitransparent devices from the perspective of molecular structures, mainly by broadening the absorption window of non-fullerene small molecule acceptors, thus improving the crystallinity and charge mobility of small molecules, and regulating the stacking behavior and orientation of molecules in the films. Second, regarding the active layer processing, much effort has been undertaken to optimize the light absorption, morphology, and charge carrier transport channels of blended films.

The gradual increase of CO₂ concentration in the atmosphere is believed to have a profound impact on the global climate and environment. To address this issue, strategies toward effective CO₂ conversion have been developed. As one of the most available strategies, the CO₂ electrochemical reduction approach is particularly attractive because the required energy can be supplied from renewable sources such as solar energy. Electrochemical reduction of CO₂ to chemical feedstocks offers a promising strategy for mitigating CO₂ emissions from anthropogenic activities; however, a critical challenge for this approach is to develop effective electrocatalysts with ultrahigh activity and selectivity. Herein, we report the facile synthesis of a highly efficient and stable atomically isolated nickel catalyst supported by ultrathin nitrogenated carbon nanosheets (Ni-N-C) for CO₂ reduction through pyrolysis of Ni-doped metal-organic frameworks (MOFs) and dicyandiamide (DCDA). MOFs are crystalline and assembled by metal-containing nodes and organic linkers, which have a large specific surface area, tunable pore size and porosity, and highly dispersed unsaturated metal centers. Thus, Ni-doped MOFs were chosen as the precursors to endow Ni-N-C with a porous carbon structure and nickel ions. The nitrogen in Ni-N-C came from DCDA, which acts as the active site to anchor nickel ions. Because of the porous structure and numerous nitrogen sites, the Ni content of Ni-N-C was as high as 7.77% (w). There were two types of nickel ion-containing structures, including Ni⁺-N-C and Ni²⁺-N-C. The structure transformation of the Ni⁺-N-C species from the initial Ni²⁺ (Ni-MOF) was achieved by pyrolysis, and the ratio of Ni⁺ and Ni²⁺ varied with the pyrolysis temperature. Compared to other Ni-N-C prepared at other temperatures, Ni-N-C-800 contained more Ni⁺-N-C species that possessed the optimum *CO binding energy and thus boosted the CO desorption and evolution rate, thereby exhibiting higher CO Faradaic efficiency (FE) up to 94.6% at -0.9 V (vs. the reversible hydrogen electrode, RHE) in 0.1 mol·L^-1 KHCO₃. In addition, it has been found that the rate of CO formation on the Ni-N-C-800 electrode relies on the electrolyte concentration. With the optimal electrolyte concentration, the Ni-N-C-800 electrode achieved a superior Faraday efficiency of > 90% for CO over a wide potential range of -0.77 to -1.07 V (vs. RHE) and displayed a CO FE as high as 97.9% with a current density of 12.6 mA·cm^-2 at -0.77 V (vs. RHE) in 0.5 mol·L^-1 KHCO₃. After testing at -0.77 V for 12 h, the Ni-N-C-800 electrode maintained a CO FE of approximately 95%, indicating superior long-term stability. We believe that this study will contribute to the design and synthesis of highly catalytically active atomically dispersed monovalent metal sites for metal-N-C catalysts.

In the past few decades, lithium-ion batteries (LIBs) have dominated the market of rechargeable batteries and are extensively applied in the field of electronic devices (e.g., mobile phones and computers). However, lack of lithium resources, high cost of lithium as well as toxic and flammable organic electrolytes significantly hinder further development and large-scale application of LIBs. Therefore, it is necessary to develop next-generation green rechargeable batteries to replace LIBs. Recently, aqueous zinc-ion batteries (AZIBs) have been considered as energy storage devices with substantial development prospects for future large-scale storage systems owing to their high safety performance, low production cost, abundant zinc resources, and environmental friendliness. Typically, we use zinc metal as the anode with neutral or weakly acidic aqueous electrolyte (pH: 3.6–6.0). However, cathode materials have high requirements for AZIBs while considering the charge effect of multivalent metal ions. Currently, one of the research emphases is to develop suitable zinc ion intercalation cathode materials with stable structures and high capacities. Among all types of cathode materials, vanadium-based compounds have the advantages of low cost and high reversible capacity. Additionally, their structure is variable, mainly including layered, tunneled and natrium super ionic conductor (NASICON) structure. Therefore, vanadium-based compounds have clear application possibility in AZIBs. However, there are still several significant problems. In particular, vanadium-based compounds generally have poor conductivity and low voltage platform. Electrochemical performance can be significantly improved mainly by pre-inserting metal ions or water molecules, optimizing the electrolyte, and controlling morphology of nanomaterials (nanosheets, nanospheres, etc.). In addition, the zinc storage mechanism in vanadium-based compounds is more complicated and controversial, including Zn²⁺ intercalation/deintercalation mechanism, co-insertion mechanism, and conversion reaction mechanism. Moreover, different materials usually exhibit different electrochemical properties and energy storage mechanisms. In this review, we comprehensively describe the energy storage mechanisms of vanadium-based compounds and discuss the application as well as development status of vanadium-based materials in AZIBs. Further, several strategies for improving their performance are proposed, including structural design (e.g., pre-insertion of metal ions or water molecules), morphology control (e.g., carbon coating), and electrolyte optimization (e.g., adjustment of composition and concentration). In particular, pre-insertion of metal ions or water molecules in the original structure can effectively solve these problems of low ion diffusion rate, poor conductivity, and structural instability, thereby achieving excellent electrochemical performance. Moreover, the application of a high-concentration electrolyte is a simple and effective strategy that can not only significantly widen the electrochemical stability window of the aqueous electrolyte but also suppress the dissolution of vanadium, thereby effectively improving energy density and cycling stability for AZIBs. Accordingly, the future development direction of AZIBs and their vanadium-based cathode materials is further prospected, aiming at designing high-performance electrode materials for AZIBs.

The implementation of clean energy techniques, including clean hydrogen generation, use of solar-driven photovoltaic hybrid systems, photochemical heat generation as well as thermoelectric conversion, is crucial for the sustainable development of our society. Among these promising techniques, electrocatalysis has received significant attention for its ability to facilitate clean energy conversion because it promotes a higher rate of reaction and efficiency for the associated chemical transformations. Noble-metal-based electrocatalysts typically show high activity for electrochemical conversion processes. However, their scarcity and high cost limit their applications in electrocatalytic devices. To overcome this limitation, binary catalysts prepared by alloying with transition metals can be used. However, optimization of the activity of the binary catalysts is considerably limited because of the presence of the miscibility gap in the phase diagram of binary alloys. The activity of binary electrocatalysts can be attributed to the adsorption energy of molecules and intermediates on the surface. High-entropy alloys (HEAs), which consist of diverse elements in a single NP, typically exhibit better physical and/or chemical properties than their single-element counterparts, because of their tunable composition and inherent surface complexity. Further, HEAs can improve the performance of binary electrocatalysts because they exhibit a near-continuous distribution of adsorption energy. Recently, HEAs have gained considerable attention for their application in electrocatalytic reactions. This review summarizes recent research advances in HEA nanostructures and their application in the field of electrocatalysis. First, we introduce the concept, structure, and four core effects of HEAs. We believe that this part will provide the basic information about HEAs. Next, we discuss the reported top-down and bottom-up synthesis strategies, emphasizing on the carbothermal shock method, nanodroplet-mediated electrodeposition, fast moving bed pyrolysis, polyol process, and dealloying. Other methods such as combinatorial co-sputtering, ultrashort-pulsed laser ablation, ultrasonication-assisted wet chemistry, and scanning-probe block copolymer lithography are also highlighted. Among these methods, wet chemistry has been reported to be effective for the formation of nano-scale HEAs because it facilitates the concurrent reduction of all metal precursors to form solid-solution alloys. Next, we present the theoretical investigation of HEA nanocatalysts, including their thermodynamics, kinetic stability, and adsorption energy tuning for optimizing their catalytic activity and selectivity. To elucidate the structure–property relationship in HEAs, we summarize the research progress related to electrocatalytic reactions promoted by HEA nanocatalysts, including the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, methanol oxidation reaction, and CO₂ reduction reaction. Finally, we discuss the challenges and various strategies toward the development of HEAs.

The Li metal anode is considered the most promising anode for next-generation high energy density batteries owing to its high theoretical capacity and low electrode potential. The development of batteries with high energy density is essential to meet the growing demand for energy storage devices in the modern world. However, the Li metal anode has operational problems. The high activity of Li causes dendritic growth during the cycling process, which leads to the cracking of the SEI (solid-electrolyte interphase), increased side reactions, and formation of dead Li. Furthermore, if the growth of Li dendrites is left uncontrolled, it can penetrate the separator and create a short-circuit accompanied by thermal runaway. Additionally, the complete utilization of active Li is challenged by the infinite volume expansion of the Li anode. To improve the application scope of Li metal batteries, it is imperative to develop advanced strategies for inhibiting Li dendritic growth, enhancing the stability of the SEI, reducing the accumulation of dead Li, and buffering the volume expansion. Understanding the mechanisms and models of Li nucleation and growth provides insight into solving these problems. This review summarizes some of the important models of Li nucleation and growth such as the surface nucleating model, charge-induced model, SEI model, and deposition/dissolution model. These models aid comprehension of the Li nucleation and growth process under various conditions. This review also discusses the strategies explored in the literature for improving the electrodes (such as three-dimensional (3D) matrix), electrolyte, SEI, and separator to realize uniform deposition of Li and improved utilization of Li. The 3D matrix strategy for improving the electrode design explores various matrices including graphene-based, carbon fiber-based, porous metal-based, and powder-based for buffering the volume expansion and reducing the local current density. To improve the electrolyte, concentrated lithium salts and functional additives are employed to stabilize the SEI and inhibit dendritic growth by regulating the chemical composition of SEI and inducing the deposition of Li. With respect to improving the design of the SEI, strategies for the construction of inorganic or organic components with high ionic conductivity and stable structure are explored for even distribution of Li ions and to avoid SEI rupture. This can reduce electrolyte consumption and dead Li formation. The modification of the separator by functional nanocarbon layer can control the direction of dendritic growth, thereby preventing the penetration of dendrites into the separator and achieving a uniform Li deposition layer. Finally, all solid state Li metal batteries (ASSLMBs) are discussed that utilize ceramic and polymer electrolytes owing to high safety of the solid state electrolyte. Therefore, reducing the interfacial resistance and suppressing dendritic growth between the Li anode and the electrolyte is key for the practical applications of ASSLMBs. Overall, this review provides a summary and outlook for promoting the practical applications of Li metal batteries.

Liquid marbles (LMs) are liquid droplets coated with a layer of lyophobic particles at the air-liquid interface. Since the pioneering work by Aussillous et al. in 2001, LMs have attracted significant attention owing to their facile fabrication, flexibility in the choice of the constituent particles and liquids, intriguing properties such as non-wetting and non-adhesive nature, satisfactory elasticity and stability, as well as promising applications in microfluidics, sensors, controlled release, and microreactors. The classical strategy for the preparation of LMs involves rolling a small volume of a droplet on a lyophobic powder bed for complete encapsulation of the liquid by the particles. In addition, various innovative methods, including electrostatic and coalescent approaches, have been developed for preparing special LMs with a complicated structure or morphology. Diverse materials such as water, surfactant solutions, liquid metals, reagents, blood, and even viscous adhesives have been employed as the internal liquid for the fabrication of LMs. Theoretically, any particulates such as lycopodium, polytetrafluoroethylene, Fe₃O₄, SiO₂, and graphite grains can be employed as the outer coating, but they are usually required to be lyophobic with sizes of less than hundreds of microns. The unique structure of the particle-covered droplet and the dual solid-liquid characteristics endow LMs with some unique and interesting properties, especially the non-wetting and non-adhesive nature. As the lyophobic coating particles restrain the internal liquid from contacting the substrate, LMs can move easily across either solid or liquid surfaces, neither wetting the substrate nor contaminating the internal liquid. An equally fascinating property of LMs is their satisfactory stability, which is necessary for most of their applications. The high stability of LMs stems from the protection of the coating powders and is embodied in both good mechanical stability (remaining intact after being released from a certain height or under a certain compression) and long lifetime (greatly suppressing the evaporation of the internal liquid). These extraordinary properties make LMs promising candidates for use in multitudinous fields, especially droplet microfluidics and microreactors. The potential application of LMs in microfluidics is ascribed to their non-wetting, non-adhesive nature and other features such as an ability to float on a liquid surface, coalescence, split, a small force of rolling friction, and response to external forces. Notably, LMs hold great promise for applications in microreactions, because they can create a confined reaction microenvironment, minimize reagent usage, facilitate unhindered gas exchange between the internal liquid medium and the surrounding environment, and allow the entry/exit of the reactants/products. We herein review the recent advances in LMs, such as manufacturing techniques, formation mechanisms, physical properties, and emerging applications. In particular, much attention is paid to the factors affecting the stability of LMs and the potential strategies to increase their stability. Moreover, this review discusses the challenges in the future development of LMs, suggests several possible ways of addressing these challenges, and forecasts the future development directions. We believe that this review can help researchers gain a better understanding of LMs and promote their further advances.

In less than a decade, metal halide perovskites (MHPs) have been demonstrated as promising solar cell materials because the photoelectric conversion efficiency (PCE) of the representative material CH₃NH₃PbI₃ rapidly increased from 3.8% in 2009 to 25.2% in 2009. However, defects play crucial roles in the rapid development of perovskite solar cells (PSCs) because they can influence the photovoltaic parameters of PSCs, such as the open circuit voltage, short-circuit current density, fill factor, and PCE. Among a series of superior optoelectronic properties, defect tolerance, i.e., the dominate defects are shallow and do not act as strong nonradiative recombination centers, is considered to be a unique property of MHPs, which is responsible for its surprisingly high PCE. Currently, the growth of PCE has gradually slowed, which is due to low concentrations of deep detrimental defects that can influence the performances of PSCs. To further improve the PCE and stability of PSCs, it is necessary to eliminate the impact of these minor detrimental defects in perovskites, including point defects, grain boundaries (GBs), surfaces, and interfaces, because nonradiative recombination centers seriously affect device performance, such as carrier generation and transport. Owing to its defect tolerance, most intrinsic point defects, such as V_I and V_MA, form shallow level traps in CH₃NH₃PbI₃. The structural and electronic characteristics of the charged point defect V_I- are similar to those of the unknown donor center in a tetrahedral semiconductor. It is a harmful defect caused by a large atomic displacement and can be passivated to strengthen chemical bonds and prevent atom migration by the addition of Br atoms. Owing to the ionic nature of MHPs and high ion migration speed, there are a large number of deep detrimental defects that can migrate to the interfaces under an electric field and influence the performance of PSCs. In addition, the ionic nature of MHPs results in surface/interface dangling bonds terminated with cations or anions; thus, deep defects can be passivated through Coulomb interactions between charged ions and passivators. Hence, the de-active deep-level traps resulting from charged defects can be passivated via coordinate bonding or ionic bonding. Usually, surface-terminated anions or cations can be passivated by corresponding cations or anions through ionic bonding, and Lewis acids or bases can be passivated through coordinated bonding. In this review, we not only briefly summarize recent research progress in defect tolerance, including the soft phonon mode and polaron effect, but also strategies for defect passivation, including ionic bonding with cations or anions and coordinated bonding with Lewis acids or bases.

A human brain is composed of a large number of interconnected neurons forming a neural network. To study the functional mechanism of the neural network, it is necessary to record the activity of individual neurons over a large area simultaneously. Brain-computer interface (BCI) refers to the connection established between the human/animal brain and computers/other electronic devices, which enables direct interaction between the brain and external devices. It plays an important role in understanding, protecting, and simulating the brain, especially in helping patients with neurological disorders to restore their impaired motor and sensory functions. Neural electrodes are electrophysiological devices that form the core of BCI, which convert neuronal electrical signals (carried by ions) into general electrical signals (carried by electrons). They can record or interfere with the state of neural activity. The Utah Electrode Array (UEA) designed by the University of Utah is a mainstream neural electrode fabricated by bulk micromachining. Its unique three-dimensional needle-like structure enables each electrode to obtain high spatiotemporal resolution and good insulation between each other. After implantation, the tip of each electrode affects only a small group of neurons around it even allowing to record the action potential of a single neuron. The availability of a large number of electrodes, high quality of signals, and long service life has made UEA the first choice for collecting neuronal signals. Moreover, UEA is the only implantable neural electrode that can record signals in the human cerebral cortex. This article mainly serves as an introduction to the construction, manufacturing process, and functioning of UEA, with a focus on the research progress in fabricating high-density electrode arrays, wireless neural interfaces, and optrode arrays using silicon, glass, and metal as that material of construction. We also discuss the surface modification techniques that can be used to reduce the electrode impedance, minimize the rejection by brain tissue, and improve the corrosion resistance of the electrode. In addition, we summarize the clinical applications where patients can control external devices and get sensory feedback by implanting UEA. Furthermore, we discuss the challenges faced by existing electrodes such as the difficulty in increasing electrode density, poor response of integrated wireless neural interface, and the problems of biocompatibility. To achieve stability and durability of the electrode, advancements in both material science and manufacturing technology are required. We hope that this review can broaden the scope of ideas for the development of UEA. The realization of a fully implantable neural microsystem can contribute to an improved understanding of the functional mechanisms of the neural network and treatment of neurological diseases.

Adlayer chemistry has been a significant subject of interest in physical chemistry over the past decades. Considerable attention has been paid to the development of high-performance film-based gas sensors, and tremendous progress has been achieved. Among the different analytical techniques, fluorescence provides a highly sensitive and selective method for detecting a wide variety of analytes. Film-based fluorescent sensors have emerged as one of the most promising candidates for chemical sensing and are being further developed into portable devices. Theoretically, relative signal changes including static and dynamic characteristics are significantly used to determine the sensing process; these characteristics are associated with surface absorption, the interaction between the analytes and sensing adlayer, as well as desorption kinetics in the absence and presence of the targeted gaseous analytes. As revealed earlier, there are a number of factors that determine the sensing behavior of a film, and the most important factors have been identified. Firstly, the suitability of the employed sensing fluorophore, which is important as it ultimately determines the effectiveness of a sensing process. Secondly, the structure of the fluorescent adlayer of the film; this is another important factor as it significantly determines the efficiency of mass transfer, which is necessary for efficient and reversible sensing. Finally, the chemical nature and surface structure of the substrate as these could affect the sensing performance of the film via the screening or enriching of analyte molecules. However, in situ, online, fast, and sensitive detection and discrimination of toxic and hazardous species via vapor sampling is a challenge that will persist for many years. By using the simultaneous interaction of multiple analytes with different sensing materials, the sensor array-based approach can recognize the overall change in the composition of complex mixtures, rather than just identifying their specific elements. The data-rich outputs of array-based sensing methods have recently been widely adopted by the analytical community due to their improved capabilities with statistical and cheminformatic approaches during analysis. Moreover, the community has recognized that numerous complex sensing challenges cannot be solved with conventional analytical tools.

In the past 20 years, our group has been committed to effectively research the formation of fluorescent sensitive films, optimization of sensing films, and fabrication of film-based fluorescent sensor arrays. A series of fluorescence sensitive thin-film materials have been developed, and high-performance fluorescence sensors have been successfully fabricated due to which a positive technological transformation has been achieved. Based on the recent progress in our group, this article briefly reviews the key points of the interactions between the gaseous analytes and adlayer. Moreover, their applications have also been addressed in the vapor phase detection of explosives, illicit drugs, and volatile organic contaminants based on the film-based fluorescent gas sensors. Further discrimination of the complex analytes was realized using a sensor array and pattern recognition strategy. It is strongly believed that our studies are the first to provide powerful fluorescent techniques for the efficient detection and discrimination of important or hazardous substances with remarkably different properties. Meanwhile, the large-scale production of our development demonstrates that interdisciplinary corporation and industry participation plays a vital role in converting laboratory techniques to a conceptual sensing system, which can manufacture commercial portable detectors. Furthermore, we offer insights on the future directions and challenges of film-based sensors in gas sensing.

The electrocatalytic CO₂ reduction reaction (CO₂RR) driven by renewable energy is an efficient approach to achieve the conversion and utilization of CO₂. In this context, CO₂RR has become an emerging research focus in the field of electrocatalysis over the past decade. While a large number of nanostructured catalysts have been developed to accelerate CO₂RR, the tradeoff between activity and selectivity usually renders the overall electrocatalytic performance very poor. Beyond catalyst design, rationally designing electrolyzers is also of substantial importance for improving the CO₂RR performance and achieving its scale-up for practical applications. To a large extent, the electrolyzer configuration determines the local reaction environment near an electrode by affecting the process conditions, thereby resulting in remarkably different electrocatalytic performances. To be techno-economically viable, the performance of CO₂ electrolyzers is expected to be at least comparable to that of the current state-of-the-art proton exchange membrane (PEM) water electrolyzers, with regard to their activity, selectivity, and stability. Researchers have made great progress in the development of CO₂ electrolyzers over the past few years, but they are also facing many issues and challenges. This review aims to provide an in-depth analysis of the research progress and status of current CO₂ electrolyzers including H-cell, flow-cell, and membrane electrode assembly cell (MEA-cell) electrolyzers. Herein, operation at industrial current densities (> 200 mA∙cm⁻²) is set as a basis when these electrolyzers are discussed and compared in terms of the four main figures of merit (current density, Faradic efficiency, energy efficiency and stability) that describe the CO₂RR performance of an electrolyzer. The advantages and drawbacks of each electrolyzer are discussed and highlighted with emphasis on the key achievements reported to date. Compared to conventional H-cell electrolyzers that work well in mechanistic studies, the newly developed electrolyzers using gas diffusion electrodes, both flow-cell and MEA-cell electrolyzers, are able to break the limitation of CO₂ solubility in water and acquire industrial current densities. Although flow-cell electrolyzers have achieved current densities exceeding 1 A∙cm⁻², they suffer from low energy efficiencies because of the significant iR drop and poor stability owing to the use of alkaline electrolytes. These issues can be overcome in the case of zero-gap MEA-cell electrolyzers with ion exchange membranes being as solid electrolytes. The anion exchange membrane (AEM)-based CO₂ electrolyzers are at the center of the current research, as they demonstrate promising activity and selectivity toward specific CO₂RR products and exhibit excellent stability for over thousands of hours in few cases. Meanwhile, the crossover of CO₂ and liquid products from the cathode to the anode through the membrane tends to lower the utilization efficiency of the CO₂ supplied to the AEM electrolyzers. MEA-cell electrolyzers using cation exchange membranes and bipolar membranes have also been explored; however, neither of them have shown satisfactory CO₂RR performance. The development of new polymer electrolyte membranes and ionomers would help address these problems. While issues and challenges still exist, MEA-cell electrolyzers hold the greatest promise for practical applications. As concluding remarks, research strategies and opportunities for the future have been proposed to accelerate the development of CO₂RR technology for practical applications and to deepen the mechanistic understanding behind improved performance. This review provides new insights into rational electrolyzer design and guidelines for researchers in this field.

Metal halide perovskites are considered as promising candidates for lighting applications owing to their excellent optoelectronic properties, such as high electron/hole mobility, high photoluminescence quantum yield, high color purity, and facile color tunability. In recent years, perovskite light-emitting diodes (LEDs) have developed rapidly, and their external quantum efficiencies (EQEs) have exceeded 20% for green and red emissions. However, the EQEs and stabilities of blue (particularly deep-blue) perovskite LEDs are still inferior to the green and red counterparts, which severely restricts the application of perovskite LEDs in high-performance and wide color gamut displays as well as white light illumination. Therefore, summarizing the development of blue perovskite LEDs and discussing the opportunities and challenges associated with their future applications will help to guide the further development of the entire perovskite LED field. In this review, according to the emission color, we divide the blue perovskite LEDs into three parts for a better discussion, i.e., the emissions in the sky-blue, pure-blue, and deep-blue regions. We introduce their developed history and discuss the basic strategies to achieve blue emission. There are three typical methods to obtain perovskite emitters with blue emission, i.e., (1) composition engineering, (2) dimensional engineering, and (3) synthesis of perovskite nanocrystals and quantum dots. For composition engineering, changing ions in perovskite ABX₃ structure can easily tune the perovskite emission color, particularly while changing the anions in "X" position. Therefore, modulating the ratio between the X-site anions of Br^- and Cl^- can cause perovskites to emit blue photons ranging from 420 to 490 nm, which almost covers the entire blue spectrum. For dimensional engineering, perovskite materials can form a series of low-dimensional structures (layered structures) with the insertion of organic ligands between the perovskite frameworks. This type of low-dimensional perovskite material typically exhibits better lighting properties than those exhibited by its three-dimensional counterpart owing to its unique charge or energy transfer process of charge carriers. Blue perovskite nanocrystals and quantum dots with high photoluminescence quantum yields are excellent candidates for realizing high-performance pure-blue and deep-blue devices because they can easily incorporate Cl^- in their crystals, which is considerably limited in perovskite thin films owing to the poor solubility of inorganic chloride sources in polar solvents. Furthermore, we discuss several challenges associated with blue perovskite LEDs, such as the inferior device performance in the pure-blue and deep-blue regions, difficulty in hole injection, electroluminescence (EL) instability of mixed halide perovskite systems, and lagged operation lifetime, and introduce potential solutions accordingly. Note that the challenges faced by blue perovskite LEDs are also the opportunities for research in this area. Therefore, this review is of a great reference value for the next evolution of blue perovskite LEDs.

As the application of lithium-ion batteries in advanced consumer electronics, energy storage systems, plug-in hybrid electric vehicles, and electric vehicles increases, there has emerged an urgent need for increasing the energy density of such batteries. Lithium metal anode is considered as the "Holy Grail" for high-energy-density electrochemical energy storage systems because of its low reduction potential (-3.04 V vs standard hydrogen electrode) and high theoretical specific capacity (3860 mAh·g^-1). However, the practical application of lithium metal anode in rechargeable batteries is severely limited by irregular lithium dendrite growth and high reactivity with the electrolytes, leading to poor safety performance and low coulombic efficiency. Recent research progress has been well documented to suppress dendrite growth for achieving long-term stability of lithium anode, such as building artificial protection layers, developing novel electrolyte additives, constructing solid electrolytes, using functional separator, designing composite electrode or three-dimensional lithium-hosted material. Among them, the use of electrolyte additives is regarded as one of the most effective and economical methods to improve the performance of lithium-ion batteries. As a natural polyphenol compound, tannic acid (TA) is significantly cheaper and more abundant compared with dopamine, which is widely used for the material preparation and modification in the field of lithium-ion batteries. Herein, TA is first reported as an efficient electrolyte film-forming additive for lithium metal anode. By adding 0.15% (mass fraction, wt.) TA into the base electrolyte of 1 mol·L^-1 LiPF₆-EC/DMC/EMC (1 : 1 : 1, by wt.), the symmetric Li|Li cell exhibited a more stable cyclability of 270 h than that of only 170 h observed for the Li|Li cell without TA under the same current density of 1 mA·cm^-2 and capacity of 1 mAh·cm^-2 (with a cutoff voltage of 0.1 V). Electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), and energy-dispersive X-ray spectroscopy (EDS) analyses demonstrated that TA participated in the formation of a dense solid electrolyte interface (SEI) layer on the surface of the lithium metal. A possible reaction mechanism is proposed here, wherein the small amount of added polyphenol compound could have facilitated the formation of LiF through the hydrolysis of LiPF₆, following which the resulting phenoxide could react with dimethyl carbonate (DMC) through transesterification to form a cross-linked polymer, thereby forming a unique organic/inorganic composite SEI film that significantly improved the electrochemical performance of the lithium metal anode. These results demonstrate that TA can be used as a promising film-forming additive for the lithium metal anode.

With the development of human society and economy, the demand for energy resources has also increased rapidly. However, the use of traditional fossil energy leads to high amounts of carbon dioxide emissions, causing severe greenhouse effects. This, in turn, triggers a series of environmental problems. Harnessing renewable energy such as solar energy, wind energy, and hydropower to replace the traditional energy sources is very urgent. Conversion CO₂ into value-added fuels and chemicals could be a useful strategy to mitigate the current energy and environmental crisis. It is well known that Cu-based materials are good electrocatalysts for the electrochemical reduction of CO₂ (ECR-CO₂). However, they suffer from some disadvantages such as high overpotential and poor selectivity and durability. Therefore, the development of copper based electrocatalysts with high activity and selectivity is essential.

Metal-organic frameworks (MOFs) materials that have the advantages of large specific surface area, tunable pore size and porosity, and highly dispersed unsaturated metal centers can be used as electrocatalysts for CO₂ reduction or as precursors for further preparation of catalysts with excellent performance. Through thermal decomposition in an inert atmosphere, metal ions in MOF can be transformed into metal clusters, metal oxides, or even metal mono-atoms. Meanwhile, organic ligands are carbonized into porous carbon materials. The addition of some heteroatoms such as B, N, P, and S to carbon materials has also been shown to be effective in changing the electron state and coordination structure of the catalysts. These heteroatoms combine with carbon atoms to form a new active site, denoted as M-X-C (M is the central metal ion and X is the mixed heteroatom) to enhance the catalytic activity of the ECR-CO₂.

Herein, pre-synthesized Cu-NBDC MOF (a Cu-based MOF synthesized by using 2-aminoterephthalic acid (NBDC) as ligand) is used as a precursor to anchor Cu₂O/Cu on nitrogen doped porous carbon (Cu₂O/Cu@NC) by annealing at different temperatures. XPS analysis shows that the Cu-N content in Cu₂O/Cu@NC decreases with increasing annealing temperature. Investigation of the ECR-CO₂ reveals that Cu₂O/Cu@NC can inhibit the HER more effectively compared to Cu₂O/Cu@C, thereby improving the overall catalytic activity and multi-electron product selectivity of the ECR-CO₂. While the Faradic efficiency of formate (FE_formate) increases with increasing temperature, those of ethylene and methane (FE_C2H4 and FE_CH4, respectively) decreases with increasing temperature. Specifically, upon annealing at 400 ℃, the CO₂ Faradic efficiency of Cu₂O/Cu@NC-400 is higher than 86% (−1.4 to −1.6 V vs. RHE), including 20.4% of FE_C2H4 (−1.4 V vs. RHE) and 23.9% of FE_CH4 (−1.6 V vs. RHE). By contrast, FE_CH4 (−1.6 V vs. RHE) in the presence of Cu₂O/Cu@C-400 without nitrogen doping is only 2.33%, and no C₂H₄ is detected. These significant differences in the catalytic behavior can be attributed to the fact that Cu-N is conducive for the stable adsorption of the *CH₂ intermediate during the ECR-CO₂, thus inhibiting the evolution of H₂. These results indicate that the pathway of the ECR-CO₂ and its performance can be effectivel regulated by complexing nitrogen with Cu motifs.

Peptide-based supramolecular colloids are assembled systems based on weak interactions between peptides (such as hydrogen bonding, electrostatic forces, hydrophobic effects, π–π interactions, and van der Waals forces), spontaneously formed in a bottom-up manner. Peptide-based supramolecular colloids have ordered molecular arrangements and regular structures, with characteristics of both traditional colloids and supramolecular systems. Constructing functional supramolecular colloids via weak intermolecular interactions assists in understanding the process of biomolecular self-assembly in vivo and provides an effective strategy for designing supramolecular materials with excellent performance. Peptides, consisting of several amino acids, are elegant building blocks in supramolecular chemistry as well as colloid and interface chemistry because of their biological origin, clear composition, low immunogenicity, structural programmability, excellent biosafety, and high biodegradability. Based on the approach of supramolecular self-assembly, peptides can be manipulated to form multiscale and multifunctional colloidal systems, which have widespread applications in medicine, catalysis, energy, nanotechnology, and other fields. However, the realization of precise control of the structures and functions of these supramolecular colloids through peptide design and intermolecular interactions regulation remains an important issue to be addressed. To study the assembly process and physicochemical mechanism of supramolecular colloids at the molecular scale, and to explore the relationship between colloidal structure and function, the construction and functionalization of supramolecular colloids must be achieved. This work is a systematic summary of the assembly mechanism, structures, and functions as well as the state of the art of peptide-based supramolecular colloids with emphasis on the regulation of intermolecular interactions and structure-function relationships. The research progress of peptide-based supramolecular colloids in the following fields is summarized herein: i) biomimetic photosynthesis, including light capture and charge separation; and ii) tumor phototherapies, including photothermal therapy (PTT) and photodynamic therapy (PDT). Currently, it is feasible to induce functional enhancement of peptide colloids via supramolecular assembly. The most important aspect is to design the primary structure of the peptide building block, to precisely control the weak interactions between peptide molecules and rationally optimize the self-assembly process, and control the size and structure of the assemblies. Follow-up studies should focus on the design of molecular precursors, the combination of basic research and practical application of peptide-based supramolecular colloids will be essential. The advantages of peptide-based supramolecular colloids, including their ordered organization, flexible structures, and versatile functions, will open up novel avenues for various applications of supramolecular colloids in fields such as green energy and medicine. It is hoped that this review will provide inspiration and broaden ideas to further drive the development and application of supramolecular colloids.

Lithium (Li)-based batteries are the dominant energy source for consumer electronics, grid storage, and electrified transportation. However, the development of batteries based on graphite anodes is hindered by their limited energy density. With its ultrahigh theoretical capacity (3860 mAh∙g⁻¹), low redox potential (−3.04 V), and satisfactorily low density (0.54 g∙cm⁻³), Li metal is the most promising anode for next-generation high-energy-density batteries. Unfortunately, the limited cycling life and safety issues raised by dendrite growth, unstable solid electrolyte interphase, and "dead Li" have inhibited their practical use. An effective strategy is to develop a suitable lithiophilic matrix for regulating initial Li nucleation behavior and controlling subsequent Li growth. Herein, single-atom cobalt coordinated to oxygen sites on graphene (Co-O-G SA) is demonstrated as a Li plating substrate to efficiently regulate Li metal nucleation and growth. Owing to its dense and more uniform lithiophilic sites than single-atom cobalt coordinated to nitrogen sites on graphene (Co-N-G SA), high electronic conductivity, and high specific surface area (519 m²∙g⁻¹), Co-O-G SA could significantly reduce the local current density and promote the reversibility of Li plating and stripping. As a result, the Co-O-G SA based Li anodes exhibited a high Coulombic efficiency of 99.9% at a current density of 1 mA∙cm⁻² with a capacity of 1 mAh∙cm⁻², and excellent rate capability (high current density of 8 mA∙cm⁻²). Even at a high plating capacity of 6 mAh∙cm⁻², the Co-O-G SA electrode could stably cycle for an ultralong lifespan of 1300 h. In the symmetric battery, the Co-O-G SA based Li anode (Co-O-G SA/Li) possessed a stable voltage profile of 18 mV for 780 h at 1 mA∙cm⁻², and even at a high current density of 3 mA∙cm⁻², its overpotential maintained a small hysteresis of approximately 24 mV for > 550 h. Density functional theory calculations showed that the surface of Co-O-G SA had a stronger interaction with Li atoms with a larger binding energy, −3.1 eV, than that of Co-N-G SA (−2.5 eV), leading to a uniform distribution of metallic Li on the Co-O-G SA surface. More importantly, when matched with a sulfur cathode, the resulting Co-O-G SA/lithium sulfur full batteries exhibited a high capacity of 1002 mAh∙g⁻¹, improved kinetics with a small polarization of 191 mV, and an ultralow capacity decay rate of 0.036% per cycle for 1000 cycles at 0.5C (1C = 1675 mA∙g⁻¹) with a steady Coulombic efficiency of nearly 100%. Therefore, this work provides novel insights into the coordination environment of single atoms for the chemistry of Li metal anodes for high-energy-density batteries.

In the last thirty years, Gemini surfactants with various structures have been designed, synthesized, and demonstrated to show superior physicochemical properties. However, the utilization of non-degradable surfactants, including these Gemini surfactants, poses a threat to the environment; hence, degradable Gemini surfactants are desirable. Herein, biodegradable cationic Gemini surfactants with amide or ester groups in the hydrophobic chains or the spacer were synthesized. A monomeric surfactant containing an amide group and a Gemini surfactant with amide groups both in the hydrophobic chains and the spacer were synthesized for comparison. The effects of amide group location on the aggregation behavior of Gemini surfactants were studied systematically. The differences between the Gemini surfactants with amide groups and Gemini surfactants with ester groups were evaluated by comparing their aggregation behavior and hydrogen bonding formation. The Gemini surfactants with amide groups (C₁₂A-C_n-AC₁₂) in the chains showed much larger exothermic ΔH_mic and more negative ΔG_mic values than those of the corresponding monomeric surfactant C₁₂A; besides, their critical micelle concentration (cmc) was more than one order of magnitude lower than that of C₁₂A. The amide groups located in the hydrophobic alkyl chains promoted hydrogen bonding formation and self-assembly of the Gemini surfactants C₁₂A-C_n-AC₁₂. Moreover, ¹H NMR spectra revealed that the co-effect of a short spacer and hydrogen bonding leads to slow exchange of the C₁₂A-C₂-AC₁₂ molecules between the monomer and the aggregate. For the Gemini surfactant series C₁₂-AC_nA-C₁₂, the amide groups notably increased the spacer length, and largest cmc value and smallest exothermic ΔH_mic value were observed for C₁₂-AC₂A-C₁₂ instead of C₁₂-AC₆A-C₁₂. In C₁₂-AC₁₂A-C₁₂, the spacer was long and sufficiently flexible to adopt a "U"-shaped conformation above the cmc, and it acted as the hydrophobic part of the surfactant, as confirmed by ¹H NMR spectra. Among the Gemini surfactant with amide groups in both the spacer and the hydrophobic alkyl chains, C₁₂A-AC₆A-AC₁₂ had a smaller cmc and I₁/I₃ ratio as well as more exothermic ΔH_mic values than those of C₁₂A-C₆-AC₁₂ and C₁₂-AC₆A-C₁₂. ¹H NMR spectra indicated that an ester-alcohol structural equilibrium exists during aggregation for the Gemini surfactants with ester groups. In addition, the Gemini surfactants with ester groups formed water-mediated hydrogen bonds in the aggregates. This water-mediated hydrogen bonding between ester groups was weaker than the direct hydrogen bonding between amide groups. Therefore, the Gemini surfactants with ester groups, C₁₂E-C₆-EC₁₂ and C₁₂-EC₆E-C₁₂, exhibited lower surface activity, a larger micelle ionization degree, higher micropolarity, and smaller exothermic ΔH_mic and less negative ΔG_mic values than their counterparts with amide groups, C₁₂A-C₆-AC₁₂ and C₁₂-AC₆A-C₁₂.

Since 2009, organic-inorganic halide perovskites have been widely studied in the field of optoelectric materials due to their unique optical and electrical properties. Pb-based halide perovskite solar cells (PSCs), in particular, currently have a record efficiency of 25.2%, thus showing strong potential in commercialization. However, the market prospects of PSCs have been hampered by the toxicity of lead-based materials. Therefore the seeking of less toxic and environmentally friendly elements that can replace Pb is of great interest. Tin-based perovskites are the most promising choice at present due to its similar electronic configuration as Pb, and can even have more superior semiconductor properties. As a rising star of lead-free perovskite solar cells, tin-based PSCs have drawn much attention and made promising progress during the past few years. However, it is still challenging to obtain efficient and stable tin-based PSCs because of the low defects formation energy and the oxidation of bivalent tin. Among all Pb-free perovskite materials that show photovoltaic performance, formamidinium tin tri-iodide (FASnI₃) based PSCs are the most promising because of the suitable band gap, low exciton bind energy, and high carrier mobility. The main drawbacks of tin-based perovskite material are its instability because of the easy oxidation of Sn²⁺ into Sn⁴⁺ and high dark current which arises from high p-type carrier concentration. The latter originates from the low formation energy of Sn vacancies. Many strategies have been developed to overcome these problems and promote the performance of tin-based PSCs. On one type of pursuit to avoid the oxidation of Sn²⁺, reduction additives (e.g., SnF₂, pyrazine, hydrazine vapor, hydroxybenzene sulfonic acid or its salt, and π-conjugated polymer) and solvent-free processing have been introduced and shown to be effective up to a point. In another type, Cs or Br alloying and construction of low-dimensional structures in tin-based perovskite have also been shown to be promising. In this review, the optical and electrical properties of tin-based perovskite are systematically discussed. And then, the film fabrication methods and different device architectures of tin-based PSCs are summarized. Finally, the current challenges and a future outlook for tin-based PSCs are discussed.

Inspired by the photosynthesis of green plants, various artificial photosynthetic systems have been proposed to solve the energy shortage and environmental problems. Water photosplitting, carbon dioxide photoreduction, and nitrogen photofixation are the main systems that are used to produce solar fuels such as hydrogen, methane, or ammonia. Although conducting artificial photosynthesis using man-made semiconducting materials is an ideal and potential approach to obtain solar energy, constructing an efficient photosynthetic system capable of producing solar fuels at a scale and cost that can compete with fossil fuels remains challenging. Therefore, exploiting the efficient and low-cost photocatalysts is crucial for boosting the three main photocatalytic processes (light-harvesting, surface/interface catalytic reactions, and charge generation and separation) of artificial photosynthetic systems. Among the various photocatalysts developed, the Z-scheme heterojunction composite system can increase the light-harvesting ability and remarkably suppress charge carrier recombination; it can also promote surface/interface catalytic reactions by preserving the strong reductive/oxidative capacity of the photoexcited electrons/holes, and therefore, it has attracted considerable attention. The continuing progress of Z-scheme nanostructured heterojunctions, which convert solar energy into chemical energy through photocatalytic processes, has witnessed the importance of these heterojunctions in further improving the overall efficiency of photocatalytic reaction systems for producing solar fuels. This review summarizes the progress of Z-scheme heterojunctions as photocatalysts and the advantages of using the direct Z-scheme heterojunctions over the traditional type Ⅱ, all-solid-state Z-schemel, and liquid-phase Z-scheme ones. The basic principle and corresponding mechanism of the two-step excitation are illustrated. In particular, applications of various types of Z-scheme nanostructured materials (inorganic, organic, and inorganic-organic hybrid materials) in photocatalytic energy conversion and different controlling/engineering strategies (such as extending the spectral absorption region, promoting charge transfer/separation and surface chemical modification) for enhancing the photocatalytic efficiency in the last five years are highlighted. Additionally, characterization methods (such as sacrificial reagent experiment, metal loading, radical trapping testing, in situ X-ray photoelectron spectroscopy, photocatalytic reduction experiments, Kelvin probe force microscopy, surface photovoltage spectroscopy, transient absorption spectroscopy, and theoretical calculation) of the Z-scheme photocatalytic mechanism, and the assessment criteria and methods of the photocatalytic performance are discussed. Finally, the challenges associated with Z-scheme heterojunctions and the possible growing trend are presented. We believe that this review will provide a new understanding of the breakthrough direction of photocatalytic performance and provide guidance for designing and constructing novel Z-scheme photocatalysts.

The regulation of supramolecular chirality has applications in various aspects including asymmetric catalysis, chiral sensing, optical materials and smart devices. Additionally, it provides opportunities for the simulation of important activities in living organisms and the clarification of their mechanisms. Herein, we synthesized a chiral gelator SQLG (styrylquinoxalinyl L-amino glutamic diamide) containing a π-conjugated headgroup by introducing the quinoxaline-derived moiety into L-glutamic diamide-based amphiphile via two simple condensation steps. SQLG self-assembled into nanofibers through multiple intermolecular interactions, including π–π stacking, hydrogen bonding and van der Waals interaction, leading to gelation of various organic solvents ranging from nonpolar to polar ones. Chirality transfer from the chiral center to the supramolecular level was observed when organogels formed, which manifested itself in circular dichroism (CD) spectra. The organogels formed in polar solvents such as N, N-dimethylformamide (DMF) and nonpolar solvents such as toluene exhibited opposite signals of supramolecular chirality, attributed to different hydrogen bonding strengths and thus two different types of gelator stacking modes of the gelators which was confirmed by infrared spectroscopy (IR) and X-ray diffraction (XRD). Circular polarized luminescence (CPL) denotes left-handed or right-handed circularly polarized light with different intensities emitted by the chiral luminescent system, and it characterizes the chirality of the excited state, which finds potential application in fields such as 3D optical displays, optical data storage, polarization-based information encryption and bioencoding. Owing to the strong fluorescence and supramolecular chirality, the toluene gel emitted right-handed circular polarized luminescence upon excitation, while the gel formed in DMF did not exhibit CPL emission because of its relatively weak fluorescence. Furthermore, the organogels responded rapidly and distinctly to the stimulus of acid due to the proton-accepting sites in the quinoxaline skeleton. Utilizing NMR spectroscopy, we found that the two nitrogen atoms in the quinoxaline moiety could be protonated upon acidification. During the process, intramolecular charge transfer (ICT) was significantly strengthened and the driving forces of self-assembly underwent remarkable changes, resulting in the collapse of the yellow transparent organogel into a red dispersion. Meanwhile, transformation from nanofibers to nanospheres was observed using a scanning electron microscope (SEM). With change in stacking modes in the supramolecular assembly, a complete inversion of the CD signal was detected. The CPL signal was found to be switched off, which along with the other changes of the system could subsequently be recovered by neutralization of the entire system. Therefore, we constructed a chiroptical switch with multiple stimuli-responsiveness through the introduction of an acid-sensitive π-conjugated moiety into the L-glutamic diamide-based chiral amphiphile.

Titania (TiO₂) has been among the most widely investigated and used metal oxides over the past years, as it has various functional applications. Extensive research into TiO₂ and industrial interest in this material have been triggered by its high abundance, excellent corrosion resistance, and low cost. To improve the activity of TiO₂ in heterogeneous catalytic reactions, noble metals are used to accelerate the reactions. However, in the case of nanoparticles supported on TiO₂, the active sites are usually limited to the peripheral sites of the noble metal particles or at the interface between the particle and the support. Thus, highly dispersed single metal atoms are desired for the effective utilization of precious noble metals. The study of oxide-supported isolated atoms, the so-called single-atom catalysts (SACs), was pioneered by Zhang's group. The high dispersion of precious noble metals results helps reduce the cost associated with catalyst preparation. Because of the presence of active centers as single atoms, the deactivation of metal atoms during the reaction, e.g., by coking for large agglomerates, is retarded. The unique coordination environment of the noble metal center provides special sites for the reaction, consequently increasing the selectivity of the reaction, including the enantioselectivity and stereoselectivity. Hence, supported SACs can bridge homogenous and heterogeneous reactions in solution as they provide selective reaction sites and are recyclable. Moreover, owing to the high site homogeneity of the isolated metal atoms, SACs are ideal models for establishing the structure-activity relationships. The present review provides an overview of recent works on the synthesis, characterization, and photocatalytic applications of SACs (Pt₁, Pd₁, Ir₁, Rh₁, Cu₁, Ru₁) supported on TiO₂. The preparation of single atoms on TiO₂ includes the creation of surface defective sites, surface modification, stabilization by high-temperature shockwave treatment, and metal-ligand self-assembly. Conventional characterization methods are categorized as microscopic imaging and spectroscopic methods, such as aberration-corrected scanning transmission electron microscopy (STEM), scanning tunneling microscopy (STM), extended X-ray absorption fine structure analysis (EXAFS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). We attempted to address the critical factors that lead to the stabilization of single-metal atoms on TiO₂, and elucidate the mechanism underlying the photocatalytic hydrogen evolution and CO₂ reduction. Although many fascinating applications of TiO₂-supported SACs in photocatalysis could only be addressed superficially and in a referencing manner, we hope to provide interested readers with guidelines based on the wide literature, and more specifically, to provide a comprehensive overview of TiO₂-supported SACs.

Lithium (Li) metal is considered a promising anode material for high energy density secondary Li metal batteries because it has the highest specific energy (3860 mAh·g^-1) and lowest redox potential (-3.04 V compared to standard hydrogen electrodes. However, the development of high-performance Li metal batteries is challenging. Firstly, Li dendrites tend to grow on the surface of Li metal foil, leading to a limited anodic coulombic efficiency (CE), poor cyclability, and even explosion hazards when an internal cell short circuit occurs. Moreover, Li metal suffers from serious surface stability problems and is easily corroded by electrolytes during cycling, further resulting in low CE, thus shortening the life cycle. We have developed a Li-carbon nanotube (Li-CNT) composite microsphere via a facile molten impregnation method. The Li-CNT composite's CNT framework can suppress volume changes during the charge/discharge process and help stabilize the solid electrolyte interphase (SEI), which is typically mechanically fragile. As a result, Li-CNT shows a high specific capacity (2000 mAh·g^-1) and can significantly suppress dendrite formation by reducing the current density, resulting in enhanced safety and cycling stability. However, the large specific surface area of the Li-CNT microspheres also enables increased reaction with the air and the electrolyte. A passivation layer is critical for the practical application of Li-CNT during the electrochemical cycling and manufacturing process. LiF is an important component of SEI in the liquid electrolyte system, and a uniform and dense LiF-rich SEI film can enable stable cycling. Moreover, LiF has been widely used as the preferred coating material to protect Li metal anodes through different methods. In this study, we improved the Li-CNT composite stability by constructing a uniform LiF-rich protecting layer on the surface through in situ polymerization of 4-fluorostyrene. The F functional group of 4-fluorostyrene, which is a lithiophilic group, reacts with the Li-CNT to produce a uniform LiF-rich layer on the surface of the Li-CNT via a facile and scalable liquid-phase reaction. The resulting passivation layer effectively suppresses the Li-CNT corrosion by the electrolyte and air, leading to better environmental and electrochemical stability. Consequently, after exposure to dry-air with a dew point -40 ℃ for 24 h, the specific capacity of the surface passivated Li-CNT is still as high as 1129 mAh·g^-1, corresponding to a capacity retention of 52.85%. When the surface passivated Li-CNT is paired with a LiFePO₄ cathode (the capacity ratio of cathode and anode is 1 : 6), a prolonged lifespan of over 280 cycles at 0.5C was reached, corresponding to a CE of 97.7%. The in situ polymerization passivation is simple and easy to be scale up; thus, it is a promising method for developing Li metal anodes towards the practical Li metal batteries.

Particle-stabilized dispersions such as emulsions, foams and bubbles are catching increasing attentions across a number of research areas. The adsorption mechanism and role of these colloidal particles in stabilizing the oil-water or gas-water interfaces and how these particles interact at interfaces are vital to the practical use of these dispersion systems. Although there have been intensive investigations, problems associated with the stabilization mechanisms and particle-particle interactions at interfaces still remain to explore. In this paper, we first systematically review the historical understanding of particle-stabilized emulsions or bubbles and then give an overview of the most important and well-established progress in the understanding of particle-stabilized systems, including emulsions, foams and liquid marbles. The particle-adsorption phenomena have long been realized and been discussed in academic paper for more than one century and a quantitative model was proposed in the early 1980s. The theory can successfully explain the adsorption of solid particles onto interface from energy reduction approaches. The stability of emulsions and foams can be readily correlated to the wettability of the particles towards the two phases. And extensive researches on emulsion stability and various strategies have been developed to prepared dispersion systems with a certain trigger such as pH and temperature. After that, we discuss recent development of the interactions between particles when they are trapped at the interface and highlight open questions in this field. There exists a huge gap between theoretical approaches and experimental results on the interactions of particles adsorbed at interfaces due to demanding experimental devices and skills. In practice, it is customary to use flat surfaces/interfaces as model surfaces to investigate the particle-particle at interfaces although most of the time interfaces are produced with a certain curvature. It is shown that the introduction of particles onto interfaces can generate charges at the interfaces which could possibly account for the long range electrostatic interactions. Finally, we illustrate that particle-stabilized dispersions have been found wide applications in many fields and applications such as microcapsules, food, biomedical carriers, and dry water. One of the most investigated areas is the microencapsulation of actives based on Pickering emulsion templates. The particles adsorbed at the interface can serve as interfacial stabilizers as well as constituting components of shells of colloidal microcapsules. Emulsions stabilized by solid particles derived from natural and bio-related sources are promising platforms to be applied in food related industries. Emulsion systems stabilized by solid particles of the w/w (water-in-water) feature are discussed. This special type of emulsion is attracting increasing attentions due to their all water features. Besides of oil-water interface, particle stabilized air-water interface share similar stabilization mechanism and several applications reported in the literature are subsequently discussed. We hope that this paper can encourage more scientists to engage in the studies of particle-stabilized interfaces and more novel applications can be proposed based on this mechanism

The acceleration of industrialization and the continuous upgradation of consumption structure has increased the atmospheric content of CO₂ far beyond the past levels, leading to a serious global environmental problem. Photocatalytic reduction of CO₂ is one of the most promising methods to solve the problem of rising atmospheric CO₂ content. The core of this technology is to develop efficient, environment-friendly, and affordable photocatalysts. A photocatalyst is a semiconductor that can absorb photons from sunlight and produce electron-hole pairs to initiate a redox reaction. Owing to their low specific surface areas, significant electron-hole recombination, and less surface-active sites, bulk photocatalysts are not satisfactory. Ultrathin layered materials have shown great potential for photocatalytic CO₂ reduction owing to their characteristics of large specific surface area, a large number of low-coordination surface atoms, short transfer distance from the inside to the catalyst surface, along with other advantages. Photoexcited electrons only need to cover a short distance to transfer to the nanowafer surface, and the speed of migrating electrons on the nanowafer surface is much higher than that in the layers or in the bulk catalyst. The ultrathin structure leads to significant coordinative unsaturation and even vacancy defects in the lattice structure of the atoms; while the former can be used as active sites for CO₂ adsorption and reaction, the latter can improve the separation of the electron-hole pair. This review summarizes the latest developments in ultrathin layered photocatalysts for CO₂ reduction. First, the photocatalytic reduction mechanism of CO₂ is introduced briefly, and the factors governing product selectivity are explained. Second, the existing catalysts, such as g-C₃N₄, black phosphorus (BP), graphene oxide (GO), metal oxide, transition metal dichalcogenides (TMDCs), perovskite, BiOX (X = Cl, Br, I), layered double hydroxide (LDH), 2D-MOF, MXene, and two-dimensional honeycomb-like Ge―Si alloy compounds (gersiloxenes), are classified. In addition, the prevalent preparation methods are summarized, including mechanical stripping, gas stripping, liquid stripping, chemical etching, chemical vapor deposition (CVD), template method, self-assembly of surfactant, and the intermediate precursor method of lamellar Bi-oleate complex. Finally, we introduced the strategy of improving photocatalyst performance on the premise of maintaining its layered structure, including the factors of thickness adjustment, doping, structural defects, composite, etc. The future opportunities and challenges of ultrathin layered photocatalysts for the reduction of carbon dioxide have also been proposed.

The human brain comprises over 100 billion neurons that communicate with each other via electrical activities called action potentials. Sensory perception, cognition, and behavior all emerge from these activities. Neuroengineering is a developing interdisciplinary field that employs knowledge from neurobiology, electrical and electronic engineering, materials science and engineering, computer science, and many others. Neuroengineering aims to develop tools for understanding the mechanism of brain function at the circuit level, and to further the development of neuromodulation strategy and neuroprosthetics for motor, sensory, and mental rehabilitation from disabilities and illnesses.

For high spatial and temporal resolution interfacing with neurons in the brain, implantable multielectrode arrays (MEAs) are a key member of the family of neuroengineering devices, which are designed and fabricated for in vivo electrophysiology, deep brain stimulation, and brain-computer interfaces (BCIs). On the one hand, action potential recording from MEAs can indicate the subject's mental state and movement intentions, thus enabling the BCI technology to control external motor restoration devices such as robotic arms. On the other hand, neural stimulation electrodes can modulate abnormal neural activity and treat disorders like Parkinson's disease, epilepsy, and depression. The physical and chemical properties of the electrodes, nanofabrication of arrays, and electrode–tissue interface materials are all important research subjects in translational neuroscience studies, and the utilization of nanomaterials and nanodevices continuously improves neural electrode technologies.

At present, neural interface technology is confronting numerous challenges and opportunities, especially for in vivo neural circuit analysis, neuroelectronic medicine, and functional neuromodulation. The development of neural interface devices eagerly demands super-high-density, mesoscopic recording, minimal invasion, biosignal stability, and wireless interfacing. Achievement of these next-generation neural interface technology capabilities requires collaboration between neuroscientists, neurosurgeons, material scientists, microelectronic engineers, and many others.

Since organic-inorganic halide perovskites were first used in the field of solar cells in 2009, they have emerged as the most promising high-efficiency and low-cost next-generation solar cells. However, even though conventional lead perovskite halide perovskite solar cells have achieved a record efficiency of 25.2%, there is scope for improvement in terms of the detrimental properties of their constituent heavy metals. In addition, their theoretic efficiencies are limited by the large bandgap. Tin perovskite has received considerable attention in recent years, due to its heavy-metal-free character and superior semiconductor properties, such as a suitable bandgap and a high carrier mobility. In order to fabricate tin perovskite solar cells (TPSCs) of high-efficiency, the major obstacles have to be overcome, including fast crystallization of tin perovskites, high p-type carrier concentration, and high defect density. Even if Sn²⁺ has similar electronic configuration as Pb²⁺, Sn²⁺ has two more active electrons, which render tin perovskite less stable. To deal with these problems many strategies are developed. Lewis bases, such as dimethyl sulfoxide, are widely used to slow down the crystallization rate of tin perovskite, while oxide protective layer and plentiful additives (e.g., SnF₂, liquid formic acid, and hydrazine vapor) have been found to reduce their oxidation. Furthermore, low-dimension structure and device engineering have been verified effectively promote TPSCs performance. Owing to the aforementioned strategies, the efficiency and stabilities of TPSCs were improving rapidly over the past few years, which indicates that TPSCs are the most promising candidate of lead-free perovskite solar cells. Recently, the certified efficiency of TPSCs reached over 12%, which is the maximum value for lead-free perovskite solar cells. Herein, we discuss the crystal and band structures, as well as the optoelectronic properties of tin perovskites. Furthermore, recent representative studies on tin perovskite are introduced, along with the strategies employed to improve the conversion efficiency, including the achievements based on component modification, dimension control, crystallization engineering and device structure design. Finally, we highlight the challenges presented by tin perovskites and the possible paths to improve device performance.

Recently, the problems of environmental pollution and energy shortages arise along with the rapid development of the economy, and gradually becoming significant challenges faced by society. To realize truly sustainable development, novel environment-friendly clean energy technologies need to be developed. The fuel cell is a chemical device that can directly convert the chemical energy of a fuel and an oxidant into electrical energy via an electrochemical reaction. The electrochemical reaction is usually clean and complete, and rarely produces harmful substances. Therefore, fuel cells are considered to be one of the most promising clean energy technologies. Fuel cells can be classified based on their electrolytes: alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and proton exchange membrane fuel cells (PEMFC). Although there have been many studies regarding the materials and reactions of fuel cells, direct spectroscopic evidence to understand the reaction mechanisms in the electrodes is lacking. Raman spectroscopy, as a non-destructive molecular spectroscopy technique with ultra-high sensitivity, is suitable for studying fuel cell materials. Over the past decade, the development of surface-enhanced Raman spectroscopy (SERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) has overcome the material and morphology limitations of traditional Raman spectroscopy. The extraordinary progress in SHINERS has enabled researchers to acquire high-quality Raman spectra for many types of materials instead of only on the surface of noble metals such as Au, Ag, and Cu. This strategy can also be applied to trace intermediate reactants on electrodes to fully understand the reaction mechanism of the fuel cell. Although many kinds of characterization methods including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and X-ray diffraction (XRD) also exhibit excellent sensitivity for studying electrode reactions, they require material pretreatments and long-duration experiments. Compared with the abovementioned methods, SERS and SHINERS show better performance for in situ experiments, which will aid in the rational design of catalysts and electrode materials with higher efficiency. This article provides an overview of the basic concepts of fuel cells, as well as SERS and SHINERS. In addition, the application of Raman spectroscopy, SERS, and SHINERS in fuel cell development is discussed along with future prospects.

Nervous system injury can disrupt communications between neurons, leading to loss of basic nerve functions and even paralysis. The clinical prognosis of nervous system injury is usually poor. This adversely affects the physical and mental health of patients and their families, and causes serious economic losses to the society. Due to slow and incomplete healing, the regenerative capacity of the nervous system is limited. Despite development of various biomedical treatment options such as, stem cell transplantation, neurotrophic factors and scaffold application, it is still very difficult to achieve adequate therapeutic effects that can benefit clinical practice. It is worth noting that nervous system components are closely related to electric fields (EFs), and a fundamental property of neurons is plasticity in response to endogenous and exogenous electrical stimulations. Electrical stimulation has been applied by researchers to induce nerve repair. This review summarizes the progress in research on EFs on neurons and applications of EFs in the treatment of peripheral nerve system and central nerve system injuries, focusing on the methods and effects of electrical stimulation. Research using direct, alternating, and pulsed EFs, with various parameters, has all demonstrated its positive effects on nerve healing and motor function recovery. Research on nanogenerators (NGs), a novel electrical stimulation technology that can convert mechanical energy into electrical energy, has achieved great progress in recent years. In biomedicine, NGs can collect the mechanical energy of human motion and convert it into electrical stimulations without requiring an external power supply, which can lead to significant innovations in electrical stimulation therapy. This review also discusses the recent applications of NGs in the treatment of nervous system diseases. NGs can be used to fabricate miniature, ultra-thin, flexible, and biodegradable healthcare devices according to different application scenarios such as in vivo or in vitro. NGs have enabled specific applications in deep brain stimulation, peripheral nerve stimulation, muscle stimulation, and sensory substitution to restore nervous system function. In order to apply electrical stimulation therapy in the clinical setting and improve the quality of life of patients with neurological injuries, further research into stimulation devices and their settings and parameters is highly desirable.

As an ideal negative electrode material for next-generation high-energy-density batteries, lithium (Li) metal has received extensive attention from the global research community. However, the safety hazards and short cycle life caused by the growth of Li dendrites have seriously hampered the application of Li metal batteries. Based on electrochemical phenomena and theory, this paper discusses the mechanism of dendritic growth, dead Li formation, and full battery failure from the perspective of concentration polarization. During the electrodeposition process, the consumption of Li ions on the surface induces concentration polarization. After the initial deposition, a relatively loose dendrite layer appears on the Li metal surface; the electrolyte can penetrate this dendrite layer to reach the dense Li metal surface. When the grown dendrites penetrate the concentration polarization layer, the interface concentration battery is short-circuited. In this case, the concentration difference battery tends to release all stored power and reach a potential balance between the high- and low-concentration regions, which causes the deposition of Li ions over the dendrites to reduce the ion concentration in the surrounding electrolyte. Meanwhile, the dissolution of Li ions that occurs at the roots of the dendrites increases the local ion concentration. This process accelerates the formation of a dead Li layer. A similar electrochemical process often occurs in columnar Li, as reported in other studies. When columnar Li is cycled several times, each Li column degenerates into a matchstick shape with a large head and thin neck. Therefore, eliminating concentration polarization is necessary for the application of columnar Li. Furthermore, in this work, concentration polarization and dendrite suppression in state-of-the-art porous host electrodes are analyzed. The larger specific surface area of the porous electrode greatly reduces the local current density on the electrode surface, which can reduce the interface concentration polarization and thus prevent dendrite growth. In charge-discharge cycling, a constant-voltage charging or shelving step is often inserted in each cycle in order to eliminate the influence of concentration polarization. However, if a dendritic layer has been formed on the Li metal surface after charging, in addition to the self-diffusion of ions, the self-discharge process of the interface concentration battery causes the detachment of the dendrite layer, thus resulting in the above-mentioned dead Li. Therefore, a larger amount of deposited Li yields a thicker Li dendritic layer, thus accelerating the capacity decay and failure of the battery, especially to those with high-capacity, high-voltage positive electrodes. The conclusions obtained in this paper can provide a theoretical basis for researchers to further explore Li metal protection strategies.

Since their discovery, two-dimensional (2D) materials have attracted significant research attention owing to their excellent and controllable physical and chemical properties. These materials have emerged rapidly as important material system owing to their unique properties such as electricity, optics, quantum properties, and catalytic properties. 2D materials are mostly bonded by strong ionic or covalent bonds within the layers, and the layers are stacked together by van der Waals forces, thereby making it possible to peel off 2D materials with few or single layers. The weak interaction between the layers of 2D materials also enables the use of van der Waals gaps for regulating the electronic structure of the system and further optimizing the material properties. The introduction of guest atoms can significantly change the interlayer spacing of the original material and coupling strength between the layers. Also, interaction between the guest and host atom also has the potential to change the electronic structure of the original material, thereby affecting the material properties. For example, the electron structure of a host can be modified by interlayer guest atoms, and characteristics such as carrier concentration, optical transmittance, conductivity, and band gap can be tuned. Organic cations intercalated between the layers of 2D materials can produce stable superlattices, which have great potential for developing new electronic and optoelectronic devices. This method enables the modulation of the electrical, magnetic, and optical properties of the original materials, thereby establishing a family of 2D materials with widely adjustable electrical and optical properties. It is also possible to introduce some new properties to the 2D materials, such as magnetic properties and catalytic properties, by the intercalation of guest atoms. Interlayer storage, represented by lithium-ion batteries, is also an important application of 2D van der Waals gap utilization in energy storage, which has also attracted significant research attention. Herein, we review the studies conducted in recent years from the following aspects: (1) changing the layer spacing to change the interlayer coupling; (2) introducing the interaction between guest and host atoms to change the physico-chemical properties of raw materials; (3) introducing the guest substances to obtain new properties; and (4) interlayer energy storage. We systematically describe various interlayer optimization methods of 2D van der Waals gaps and their effects on the physical and chemical properties of synthetic materials, and suggest the direction of further development and utilization of 2D van der Waals gaps.

Layered graphitic carbon nitride (g-C₃N₄) is a typical polymeric semiconductor with an sp² π-conjugated system having great potential in energy conversion, environmental purification, materials science, etc., owing to its unique physicochemical and electrical properties. However, bulk g-C₃N₄ obtained by calcination suffers from a low specific surface area, rapid charge carrier recombination, and poor dispersion in aqueous solutions, which limit its practical applications. Controlling the size of g-C₃N₄ (e.g., preparing g-C₃N₄ nanosheets) can effectively solve the above problems. Compared with the bulk material, g-C₃N₄ nanosheets have a larger specific surface area, richer active sites, and a larger band gap due to the quantum confinement effect. As g-C₃N₄ has a layered structure with strong in-plane C-N covalent bonds and weak van der Waals forces between the layers, g-C₃N₄ nanosheets can be prepared by exfoliating bulk g-C₃N₄. Alternatively, g-C₃N₄ nanosheets can otherwise be obtained through the anisotropic assembly of organic precursors. Nevertheless, some of these methods have various limitations, such as high energy consumption, are time consuming, and have low yield. Accordingly, developing green and cost-effective exfoliation and preparation strategies for g-C₃N₄ nanosheets is necessary. Herein, the research progress of the exfoliation and preparation strategies (including the thermal oxidation etching process, the ultrasound-assisted route, the chemical exfoliation, the mechanical method, and the template method) for two-dimensional C₃N₄ nanosheets are introduced. Their features are systematically analyzed and the perspectives and challenges in the preparation of g-C₃N₄ nanosheets are discussed. This study emphasizes the following: (1) The preparation method of g-C₃N₄ nanosheets should be properly selected according to the practical application needs. Additionally, various strategies (such as chemical method and ultrasonic method) can be combined to exfoliate nanosheets from bulk g-C₃N₄; (2) More reasonable nano- or even subnanostructured g-C₃N₄ nanosheets should be continuously explored; (3) Novel modification strategies, such as defective engineering, heterojunction construction, and surface functional group regulation, should be introduced to improve the reactivity and selectivity of the g-C₃N₄ nanosheets; (4) The application of in situ characterization techniques (such as in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), electron spin resonance (ESR) spectroscopy, and Raman spectroscopy) should also be strengthened to monitor the detailed catalytic process and investigate the g-C₃N₄ nanosheet structure-efficiency relationship. (5) To gain a deeper understanding of the relationship between the macroscopic properties and the microscopic structure, the combination of theoretical calculations and experimental results should be strengthened, which will be beneficial for exploiting high-quality g-C₃N₄ nanosheets.

Owing to the serious energy crisis and environmental problems caused by fossil energy consumption, development of high-energy-density batteries is becoming increasingly significant to satisfy the rapidly growing social demands. Lithium-ion batteries have received widespread attention because of their high energy densities and environmental friendliness. At present, they are widely used in portable electronic devices and electric vehicles. However, security aspects need to be addressed urgently. Substantial advances in liquid electrolyte-based lithium-ion batteries have become a performance bottleneck in the recent years. Traditional lithium-ion batteries use organic liquids as electrolytes, but the flammability and corrosion of these electrolytes considerably limit their development. Continuous growth of lithium dendrites can pierce the separator, leading to electrolyte leakage and combustion, which is a serious safety hazard. Replacement of organic electrolytes with solid-state electrolytes is one of the promising solutions for the development of next-generation energy storage devices, because they have high energy densities and are safe. Solid electrolytes can remarkably alleviate the safety hazards involved in the use of traditional liquid-based lithium-ion batteries. In addition, the composite of solid-state electrolytes and lithium metal is expected to result in a higher energy density. However, due to the lack of fluidity of the solid electrolytes, problems such as limited solid-solid contact area and increased impedance at the interface when solid-state electrolytes are in contact with electrodes must be solved. The localized and buried interface is a major drawback that restricts the electrochemical performance and practical applications of the solid-state batteries. Fabrication of a stable interface between the electrodes and solid-state electrolyte is the main challenge in the development of solid-state lithium metal batteries. All these aspects are critical to the electrochemical performance and safety of the solid-state batteries. Current research mainly focuses on addressing the problems related to the solid-solid interface in solid-state batteries and improving the electrochemical performance of such batteries. In this review, we comprehensively summarize the challenges in the fabrication of solid-state batteries, including poor chemical and electrochemical compatibilities and mechanical instability. Research progress on the improvement strategies for interface problems and the advanced characterization methods for the interface problems are discussed in detail. Meanwhile, we also propose a prospect for the future development of solid-state batteries to guide the rational designing of next-generation high-energy solid-state batteries. There are many critical problems in solid-state batteries that must be fully understood. With further research, all-solid-state batteries are expected to replace the traditional liquid-based lithium-ion batteries and become an important system for a safe and reliable energy storage.

Li is highly attractive anode material for next-generation high-energy-density batteries, such as Li-air, Li-sulfur, and solid-state Li-based systems because of its exceedingly low electrode potential (-3.04 V vs the standard hydrogen electrode) and ultra-high theoretical capacity (3860 mAh-g^-1). However, Li metal anodes and Li-based batteries are plagued by issues, including unstable solid electrolyte interface (SEI), dead Li formation, and uncontrollable dendritic growth. These limitations result in low cycling stability and could induce short circuits, thermal runaway, and safety hazards. In recent years, a variety of efficient strategies have been proposed to alleviate the challenges faced by Li anodes. For example, the design of Li-free anodes (with Li supplied from the lithiated cathode) or Li-composite anodes has attracted significant attention. Their population can be ascribed to the use of non-excessive Li metal that could be potentially safer and easier to produce. In Li-free and Li-composite anodes, the initial nucleation sites play a crucial role in influencing the subsequent Li electroplating behavior. Stable, homogenous Li electrodeposition is crucial for improving Coulomb efficiency and inhibiting dendrite formation. Moreover, it is also desirable to explore the nucleation and growth mechanism of Li metal on substrates or current collectors. Therefore, in this article, we aim to provide an overview of the mechanism of Li nucleation and strategies to enhance Li metal batteries via substrate modification. The mechanisms of Li nucleation are discussed in terms of nucleation-driven forces and the relation between nuclei size/distribution and overpotential/current density. Heterogeneous nucleation and Chazalviel space charge models are introduced to describe the deposition behaviors of Li in the initial nucleation stage. In the heterogeneous nucleation process, the formation of Li nuclei and its kinetics depend on the nucleation barrier, which correlates with the properties of substrates, such as their crystal structure, lattice matching, facets, and defects. The space charge model can be applied to low-concentration electrolytes or rapid Li deposition, where the decrease in ion concentration on the electrode surface induces a localized space charge and polarized electric field. This subsequently affects the microstructure and morphology of the deposited Li. After discussing the nucleation mechanism and substrate effect, strategies to stabilize nucleation and suppress dendrite are highlighted, such as three-dimensional frameworks, heterogeneous crystal nuclei, Li storage buffer layers, electric field effects, and lattice matching engineering. Information gained from the perspective of Li nucleation and the substrate effect might enlighten the development of strategies to upgrade metallic Li anodes for application in Li-based batteries.

Marine organisms such as plants, algae or small animals can adhere to surfaces of materials that are submerged in ocean. The accumulation of these organisms on surfaces is a marine biofouling process that has considerable adverse effects. Marine biofouling on ship hulls can cause severe fuel consumption increase. Investigations on antifouling polymers are therefore becoming important research topics for marine vessel operations. Antifouling polymers can be applied as coating layers on the ship hull, protecting it against the settlement and growth of sea organisms. Polyethylene glycol (PEG) is a hydrophilic polymer that can effectively resist the accumulation of marine organisms. PEG-based antifouling coatings have therefore been extensively researched and developed. However, the inferior stability of PEG makes it subject to degradation, rendering it ineffective for long-term services. Zwitterionic polymers have also emerged as promising antifouling materials in recent years. These polymers consist of both positively charged and negatively charged functional groups. Various zwitterionic polymers have been demonstrated to exhibit exceptional antifouling properties. Previously, surface characterizations of zwitterionic polymers have revealed that strong surface hydration is critical for their antifouling properties. In addition to these hydrophilic polymers, amphiphilic materials have also been developed as potential antifouling coatings. Both hydrophobic and hydrophilic functional groups are incorporated into the backbones or sidechains of these polymers. It has been demonstrated that the antifouling performance can be enhanced by precisely controlling the sequence of the hydrophobic-hydrophilic functionalities. Since biofouling generally occurs at the outer surface of the coatings, the antifouling properties of these coatings are closely related to their surface characteristics in water. Therefore, understanding of the surface molecular structures of antifouling materials is imperative for their future developments. In this review, we will summarize our recent advancements of antifouling material surface analysis using sum frequency generation (SFG) vibrational spectroscopy. SFG is a surface-sensitive technique which can provide molecular information of water and polymer structures at interfaces in situ in real time. The antifouling polymers we will review include zwitterionic polymer brushes, mixed charged polymers, and amphiphilic polypeptoids. Interfacial hydration studies of these polymers by SFG will be presented. The salt effect on antifouling polymer surface hydration will also be discussed. In addition, the interactions between antifouling materials and protein molecules as well as algae will be reviewed. The above research clearly established strong correlations between strong surface hydration and good antifouling properties. It also demonstrated that SFG is a powerful technique to provide molecular level understanding of polymer antifouling mechanisms.

Burning of fossil fuels increases CO₂ concentration in the atmosphere, resulting in a series of climate- and environment-related concerns such as global warming, sea-level rise, and melting of glaciers. Therefore, utilization of renewable energy to reduce the CO₂ concentration, in order to realize a sustainable development, is urgent. Capturing and utilizing CO₂, a greenhouse gas, can not only address these concerns but also alleviate the current scenario of energy shortage. Thermal catalytic CO₂ hydrogenation offers various pathways with high conversion efficiencies to produce fuels and industrial chemicals including CO, HCOOH, CH₃OH, and CH₄. However, CO₂ is chemically inert due to the highly stable C＝O bond. Thus, harsh reaction conditions such as high temperature and pressure are required for CO₂ hydrogenation.

Electrocatalytic CO₂ reduction using renewable electricity and water is a promising alternative to thermocatalysis. This technology can not only store and transport the intermittent solar or wind energy but can also use water as the proton source instead of H₂, which is indispensable for thermal CO₂ hydrogenation. Electrochemical CO₂ reduction under ambient conditions is a proton-coupled electron transfer process. The key to promote the electrochemical reduction of CO₂ is to develop highly selective and active catalysts with high stability. Among various CO₂ electrocatalysts, copper-based catalysts have attracted significant attention and have been extensively investigated, since they exhibit good selectivity and efficiency for the reduction of CO₂ to hydrocarbons and alcohols. A broad range of products, up to 16 different gases and liquids, can be obtained in the CO₂ electroconversion on copper. Copper is the only metal that has a negative adsorption energy for *CO and a positive adsorption energy for *H. Thus, it has a unique property of generating > 2e⁻ transfer products. However, selectivity of the target product is still low, especially for high value-added C₂₊ species (C₂H₄, C₂H₅OH, CH₃COOH, CH₃CHO, n-C₃H₇OH, etc.).

The selectivity of various products on copper-based catalysts could be enhanced by surface engineering techniques such as tuning the morphologies, particle sizes, surface facets, strains levels, and atomic coordination. Electrolyte engineering could also aid in CO₂ electroreduction. Therefore, improving the selectivity of C₂₊ products by modifying copper-based catalysts could be a hot research topic. In addition, C-C coupling is a key step in forming C₂₊ products, though the C₂₊ product formation pathway is complex, and the mechanisms are still unclear. Considering these, this paper mainly reviews the research progress in copper-based catalysts producing C₂₊ species in the last five years. It also discusses the possible reaction mechanisms and the factors that affect the product selectivities. In the end, further research directions are proposed.

Recently, the application of ReaxFF based reactive molecular dynamics simulation (ReaxFF MD) in complex processes of pyrolysis, oxidation and catalysis has attracted considerable attention. The analysis of the simulation results of these processes is challenging owing to the complex chemical reactions involved, coupled with their dynamic physical properties. VARxMD is a leading tool for the chemical reaction analysis and visualization of ReaxFF MD simulations, which allows the automated analysis of reaction sites to get overall reaction lists, evolution trends of reactants and products, and reaction networks of specified reactants and products. The visualization of the reaction details and dynamic evolution profiles are readily available for each reactant and product. Additionally, the detailed reaction sites of bond breaking and formation are available in 2D chemical structure diagrams and 3D structure views; for specified reactions, they are categorized on the basis of the chemical structures of the bonding sites or function groups in the reacting species. However, the current VARxMD code mainly focuses on global chemical reaction information in the simulation system of the ReaxFF MD, and is incapable of locally tracking the chemical reaction and physical properties in a 3D picked zone. This work extends the VARxMD from global analysis to a focused 3D zone picked interactively from the 3D visualization modules of VARxMD, as well as physical property analysis to complement reaction analysis. The analysis of reactions and physical properties can be implemented in three steps: picking and drawing a 3D zone, identifying molecules in the picked zone, and analyzing the reactions and physical properties of the picked molecules. A 3D zone can be picked by specifying the geometric parameters or drawing on a screen using a mouse. The picking of a cuboid or sphere was implemented using the VTK 3D view libraries by specifying geometric parameters. The interactive 3D zone picking was implemented using a combination of observer and command patterns in the VTK visualization paradigm. The chemical reaction tracking and dynamic radial distribution function (RDF) of the 3D picked zone was efficiently implemented by inheriting data obtained from the global analysis of VARxMD. The reaction tracking between coal particles in coal pyrolysis simulation and dynamic structure characterization of carbon rich cluster formation in the thermal decomposition of an energetic material are presented as application examples. The obtained detailed reactions between the coal particles and comparison of the reaction between the locally and globally picked areas in the cuboid are helpful in understanding the role of micro pores in coal particles. The carbon to carbon RDF analysis and comparison of the spherical region picked for the layered molecular clusters in the pyrolysis system of the TNT crystal model with the standard RDF of the 5-layer graphene demonstrate the extended VARxMD as a chemical structure characteristic tool for detecting the dynamic formation profile of carbon rich clusters in the pyrolysis of TNT. The extended capability of VARxMD for a 3D picked zone of a ReaxFF MD simulation system can be useful for interfacial reaction analysis in a catalysis system, hot spot formation analysis in the detonation of energetic material systems, and particularly the pyrolysis or oxidation processes of coal, biomass, polymers, hydrocarbon fuels, and energetic materials.

Solid-state Li metal batteries are considered promising next-generation energy storage systems due to its exceptional advantages in terms of safety and high energy density. The continuous process on the development of solid-state fast ionic electrolytes enables the solid-state battery to operate at room temperature. Among these, sulfide-based solid electrolytes have attracted significant attentions due to their extremely high ionic conductivity, excellent deformability, and mild low-temperature processability. However, the full demonstration of practical batteries remains challenging due to the slow lithium-ion transport kinetics at working solid-solid interfaces. The sluggish interfacial transport kinetics mainly result from the poor solid-solid contacts, resulting in poor battery performance. Especially for solid-state pouch cells, the high local current due to the poor contact is amplified by the high working current, leading to rapid failure. Constructing fast ion transport paths between the Li metal anode and solid electrolyte interface is key for the practical application of solid-state batteries. Here a simple protocol was developed to realize fast ionic transportation by wetting the solid electrolyte/Li metal anode interface with localized high salt concentration liquid electrolyte. First, 3.5 mmol lithium trifluoroalfonylimide (LiTFSI) was added into 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluoropropyl ether (HFE) and dimethoxyethane (DME) mixed solvent, and stirred to obtain uniformly dispersed localized high-concentration liquid electrolyte, denoted as HFE-DME LiTFSI. The fluidity of liquid electrolyte ensures sufficiently conformal contacts between lithium anode and liquid electrolyte, as well as solid-state electrolyte and liquid electrolyte. Thus, fast ion transportation channels were constructed between the solid electrolyte and Li metal anode by wetting HFE-DME LiTFSI at a concentration of 3.0 μL·cm^-2. After liquid phase therapy, the interfacial resistance of solid-state Li|Li₄Ti₅O₁₂ (LTO) pouch cell rapidly reduced from 4366 to 64 Ω·cm^-2 and even lower than the cell that was pressed at 3 MPa in the assemble process (340 Ω·cm^-2). This suggests that the ion transport kinetics are significantly improved by liquid phase therapy. Therefore, the solid-state Li metal pouch cell with dimensions of 30 mm × 30 mm showed excellent cycling performances with specific capacities of 107 and 96 mAh·g^-1 at 0.1C and 0.5C, respectively. Furthermore, the solid-state Li-S pouch cell delivered capacities of 1100 and 932 mAh·g^-1 at 0.01C and 0.02C, respectively. This study demonstrates the effectiveness of the novel liquid phase therapy to construct fast ionic transportation channels, which providing an effective strategy for the practical application of solid-state Li metal pouch cells.

Wormlike micelles and low-molecular-weight hydrogels are composed of three-dimensional networks that endow them with viscoelasticity, but their viscoelastic properties are markedly different. The viscosity of wormlike micelles is attributed to a transient network, while that of gels is due to a stable network. Under certain conditions, wormlike micelles can undergo transition to gels with an increase in the density of the network. In our previous study, we found that the wormlike micelle formed by the ionic liquid-type surfactant 1-hexadecyl-3-octyl imidazolium bromide ([C₁₆imC₈]Br) without any additive has high viscoelasticity. The inclusion of a nonionic surfactant polyoxyethylene lauryl ether (Brij 30) is expected to enhance the viscoelasticity of [C₁₆imC₈]Br wormlike micelles via electrostatic shielding and strong hydrophobic interactions, which may be the driving factor for the wormlike micelle-to-gel structural transition. The morphology and viscoelasticity of [C₁₆imC₈]Br wormlike micelles with Brij 30 were studied as a function of concentration by rheological measurements and freeze-fracture transmission electron microscopy. The thermal stability and gel-sol transition temperature of the Brij 30/[C₁₆imC₈]Br gels were studied using rheology. The interaction between Brij 30 and [C₁₆imC₈]Br was studied by zeta potential measurements and nuclear magnetic resonance (NMR) spectroscopy. Upon the inclusion of Brij 30 into the [C₁₆imC₈]Br wormlike micelles, the viscoelasticity of the Brij 30/[C₁₆imC₈]Br samples first increased and then decreased with an increase in the Brij 30 concentration, at different initial concentrations of [C₁₆imC₈]Br. At a certain Brij 30 concentration, the Brij 30/[C₁₆imC₈]Br samples rheologically behaved as a gel. The maximum viscoelasticity of the [C₁₆imC₈]Br (4.06% (w))/Brij 30 gel was observed at a Brij 30/[C₁₆imC₈]Br molar ratio of 4.55. The viscoelasticity of the Brij 30/[C₁₆imC₈]Br gels was positively correlated with the activation energy of the gels. The gel-sol transition temperature of the Brij 30/[C₁₆imC₈]Br gels also increased first and then decreased with an increase in the Brij 30 concentration. The highest gel-sol transition temperature of the Brij 30/[C₁₆imC₈]Br (4.06% (w)) gel was observed at a Brij 30/[C₁₆imC₈]Br molar ratio of 2.93. The Brij 30 concentration had a notable impact on the viscoelasticity, thermal stability, and gel-sol transition temperature of the Brij 30/[C₁₆imC₈]Br gels. The zeta potential and ¹H NMR measurements revealed that the neutral Brij 30 molecules are inserted into the palisade layer of the [C₁₆imC₈]Br wormlike micelles via hydrophobic interactions. This decreased the electrostatic repulsion between the [C₁₆imC₈]Br headgroups, which in turn induced the rapid growth of wormlike micelles and the formation of a stiffer network structure. Finally, the wormlike micelles underwent a structural transition to gels. The obtained results would aid in better understanding the relationship between wormlike micelles and gels, and may be of potential value for industrial and technological applications.

Separation and recycling of catalysts are crucial for realizing the objectives of sustainable and green chemistry but remain a great challenge, especially for enzyme biocatalysts. In this work, we report a new solvent-induced reversible inversion of Pickering emulsions stabilized by Janus mesosilica nanosheets (JMSNs), which is then utilized as a strategy for the in situ separation and recycling of enzymes. The interfacial active solid particle JMSNs is carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption experiments, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA).The JMSNs are demonstrated to show order-oriented mesochannels with a large specific surface area, and the hydrophobic octylgroup is selectively modified on one side of the nanosheets. Furthermore, the inversion is found to be a fast process that is strongly dependent on the interfacial activity of the solid emulsifier JMSNs. Such a phase inversion is also a general process that can be realized in various oil/water phasic systems, including ethyl acetate-water, octane-water, and cyclohexane-water systems. By carefully analyzing the capacity of JMSNs with different surface wettabilities for phase inversion, a triphase contact angle (θ) close to 90° and a critical oil-water ratio of 1 : 2 are identified as the key factors to achieve solvent-induced phase inversion via a catastrophic phase inversion mechanism. Importantly, this reversible phase inversion is suitable for the separation and recycling of enzyme biocatalysts that are sensitive to changes in the reaction medium. Specifically, during the reaction, the organic substrates are dissolved in the oil droplets and the water-soluble catalysts are dispersed in the water phase, while a majority of the product is released into the upper oil phase and the enzyme catalyst is confined inside the water droplets in the bottom layer after phase inversion. The perpendicular mesochannels of JMSNs provide a highly accessible reaction interface, and their excellent interfacial activity allows for more than 10 rounds of consecutive phase inversions by simply adjusting the ratio of oil to water in the system. Using the enzymatic hydrolysis kinetic resolution of racemic acetate as an example, our Pickering emulsion system shows not only a 3-fold enhanced activity but also excellent recyclability. Because no sensitive chemical reagents are used in this phase inversion process, the intrinsic activities of the catalysts can be preserved even after seven cycles. The current study provides an alternative strategy for the separation and recycling of enzymes, in addition to revealing a new innovative application for Janus-type nanoparticles.

S-scheme heterojunction is a major breakthrough in the field of photocatalysis. In this study, NiS₂ and MoSe₂ were prepared by a typical solvothermal method, and compounded by an in situ growth method to construct an S-scheme heterojunction. The obtained composite showed excellent performance in photocatalytic hydrogen evolution; the hydrogen production rate was approximately 7 mmol·h^-1·g^-1, which was 2.05 times and 2.44 times those of pure NiS₂ and MoSe₂, respectively. Through a series of characterizations, it was found that NiS₂ and MoSe₂ coupling can enhance the light absorption intensity, which is vital for the light reaction system. The efficiency of electron-hole pair separation is also among the important factors restricting photocatalytic reactions. Compared with pure NiS₂ and MoSe₂, NiS₂/MoSe₂ exhibited a higher photocurrent density, lower cathode current, and lower electrochemical impedance, which proves that the NiS₂/MoSe₂ complex can effectively promote photogenerated electron transfer. Simultaneously, the lower emission intensity of fluorescence indicated effective inhibition of electron-hole recombination in the NiS₂/MoSe₂ complex, which is favorable for the photocatalytic hydrogen evolution reaction. Further, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that MoSe₂ is an amorphous sample surrounded by the NiS₂ nanomicrosphere, which greatly increased the contact area between the two, thus increasing the active site of the reaction. Secondly, as a photosensitizer, Eosin Y (EY) effectively enhanced the absorption of light by the catalyst in the photoreaction system. Meanwhile, during sensitization, electrons were provided to the catalyst, which effectively improved the photocatalytic reaction efficiency. The establishment of S-scheme heterojunctions contributed to improving the redox capacity of the reaction system and was the most important link in the photocatalytic hydrogen reduction of aquatic products. It was also the main reason for the improvement of the hydrogen evolution effect in this study. The locations of the conduction band and valence band of NiS₂ and MoSe₂ were determined by Mott-Schottky plots and photon energy curves, and further proved the establishment of the S-scheme heterojunction. This work provides a new reference for studying the S-scheme heterojunction to effectively improve the photocatalytic hydrogen production efficiency.

Currently, because of the worldwide over-exploitation and consumption of fossil fuels, energy crisis and environmental pollution are becoming more prominent. Hence, the production and utilization of clean energy such as hydrogen are crucial. As significant electrochemical reactions in energy conversion devices, the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) have garnered considerable attention. However, the sluggish kinetics of these reactions, especially of the OER and ORR because of the multiple electron transfer steps, and the inevitable usage of noble metal catalysts (such as those based on Pt for HER/ORR and Ru/Ir for HER/OER) are the bottlenecks to realizing energy conversion devices, including overall water-splitting electrolyzers, fuel cells, and metal-air batteries. Therefore, the development of efficient non-precious metal catalysts is imperative. Transition metal nitrides (TMNs) have been recently studied and shown to exhibit high catalytic activity because of their ability to alter the electronic structure of host metals, specifically the downshift of the d-band center, the contraction of the filled state, and the broadening of the unfilled state. This high activity is attributed to the optimization of the adsorption energy between metals and adsorbates. In addition, metallic bonding in TMNs increases the conductivity of the catalysts. Thus, in this review, we focus on the latest developments in TMNs and their application as high-activity and high-stability electrocatalysts for water splitting and in fuel cells and zinc-air batteries. First, the origin of the high activity of TMNs is explained with the help of the d-band theory. The effect of nitrogen on TMNs, such as in terms of the location in the crystal structure, is briefly discussed. The preparation strategies for TMNs, including physical and chemical methods as well as the modification techniques such as doping, changing carrier properties, and defect construction, are outlined. Next, we summarize the applications of TMNs as an electrocatalyst for the HER, OER, and ORR. At the same time, to explain the bifunctional catalytic activity of TMNs, we discuss the modification strategies for single-metal-based nitrides, such as doping with other highly active atoms to adjust the electronic structure and increase the catalytic activities as well as using coupling materials with different catalytic selectivities to construct heterostructures. Finally, we discuss the challenges and development approaches for realizing the electrocatalytic applications of TMNs, such as through further improvement in catalytic activity, and for facilitating in-depth understanding of electrocatalytic processes through in situ characterization to reveal the electrocatalytic mechanism of TMNs. Undoubtedly, this review will promote the application of TMNs in the field of electrocatalysis.

Halide perovskites are ionic semiconductors with outstanding features, such as high defect tolerance, long carrier diffusion length, strong photoluminescence, narrow emission line width, solution processability, and low cost of fabrication. These advantages render them promising candidates for photovoltaics, lasers, displays, and photodetectors. Theoretical and experimental studies have demonstrated that the optical properties of perovskite materials can be strongly affected by their crystal size and dimension. Owing to their ionic nature and low formation energy, perovskites can be synthesized via precipitation. This process typically involves in situ transformation of the precursors with solvent evaporation and/or solvent mixing. It is well known that the physical/chemical properties of solvents play a vital role in determining the size and dimension of the resultant products. Therefore, elucidating the effects of the solvent on perovskite crystallization is crucial for improving the performance of perovskite-based devices. Moreover, the coordination effects between perovskite precursors and solvents are a dominant parameter that influence the crystallization process because the dissolution of perovskite precursors is strongly correlated with the coordination between the perovskite precursors and solvents. Herein, this minireview summarizes recent research advances in comprehending the perovskite precursor-solvent interactions with a focus on the coordination effects. In particular, we have endeavored to discuss the influence of coordination effects on the formation of polycrystalline thin films, quantum dots, and single crystals. It was found that the formation of perovskite-solvent intermediates in coordinated solvents retard the nucleation and growth of perovskite crystals; this proves beneficial for the fabrication of high-quality micrometer-sized perovskite polycrystalline films. Meanwhile, the preformed intermediates contribute to undesired impurities and defects in single crystals and quantum dots. These insights are exceedingly helpful for the crystallization control of perovskites, thus enabling better device performance and enhanced stability. Finally, the minireview discusses the challenges facing perovskite crystallization, along with a short perspective for future studies.

Improvement in the energy density of conventional lithium-ion batteries (LIBs), based on the intercalation-extraction chemistry of graphite and transition metal layered oxides, has apparently lagged behind the advances in consumer electronics and electric vehicles. Secondary Li-metal batteries (LMBs), utilizing metallic Li as the anode material, have incomparable advantages in terms of energy density due to their high specific capacity (3860 mAh·g^-1) and low redox potential (-3.04 V vs. standard hydrogen electrode) of Li metal. Irrespective of whether Li anodes are coupled with intercalation-type cathodes (e.g. LiFePO₄, LiCoO₂, LiNi_xCo_yMn_zO₂, etc.) or conversion-type cathodes (S, O₂), the energy density of LMBs is much higher than that of traditional LIBs, which should solve the range concern of electric vehicles. However, the intrinsically high reactivity between metallic Li and organic electrolytes could induce the formation of a solid electrolyte interface (SEI). The heterogeneous SEI, consisting of a flexible organic outer layer and a brittle inorganic inner layer, suffers from repeated rupture and regeneration due to infinite volume expansions associated with Li deposition and dissolution reactions. Meanwhile, Li is preferentially deposited on the "hot sites" and is stripped from the root of sediments, resulting in uncontrolled dendrite growth during charging and formation of electrochemically isolated Li ("dead" Li) during discharging. Thus, the Columbic efficiency of Li metal full cells is greatly limited by interfacial side effects and continuous loss of active Li, especially in conventional carbonate-based electrolyte, viz. 1 mol·L^-1 LiPF₆-EC/DEC (ethylene carbonate/diethyl carbonate), which impedes the large-scale employment of Li metal batteries. Recently, novel electrolytes with high or localized-high salt concentrations have attracted considerable attention because of their unique physiochemical properties and excellent electrochemical performance. In high-concentration electrolytes, the reduction in the population of free solvent molecules inhibits irreversible electrolyte decomposition at the electrode-electrolyte interface. In localized-high-concentration electrolytes, the introduction of a dilute reagent retains the desired solvation structure, while improving the physicochemical properties (conductivity and viscosity) of the electrolyte. Herein, we systemically review the latest progress in high-concentration and localized-high-concentration electrolytes for use in Li metal batteries. The solvation chemistry structure, physicochemical properties, and interfacial-stabilizing mechanisms are analyzed in detail, and special attention is devoted to their superior interfacial compatibility with Li metal anodes. Finally, we briefly clarify the current problems associated with the research of high-concentration and localized-high-concentration electrolytes from the viewpoints of basic scientific research and practical applications, and some possible solutions are provided to further pave the way to practical Li metal batteries.

Lithium ion batteries have been widely used in the fields of portable energy storage devices and electric vehicles due to their high energy density and high safety, and have a profound impact on modern society. However, the frequent occurrence of battery fire and explosion accidents has caused widespread concern of thermal runaway and thermal safety issues. Many reviews have reported the measures to mitigate thermal runaway of lithium ion batteries. Due to the use of graphite with a smaller capacity as the negative electrode material, the specific energy of lithium ion batteries has approached the theoretical limit, and there is an urgent need to develop more efficient electrode materials to meet the growing demand of the energy storage market. Lithium metal anode has smaller density, higher theoretical capacity and lower potential, which is the ideal anode material for the next generation of high energy density battery system. However, the high reactivity of lithium will cause uncontrollable lithium dendrite growth during the cycle, which may penetrate the separator and cause internal short circuit of the battery, and then cause thermal runaway, fire and even explosion. Therefore, the thermal runaway of lithium metal batteries are more complicated and serious, which hinders the commercial application of batteries. Aiming at the thermal runaway problem of lithium metal batteries, this article first introduces the causes of thermal runaway, which are mainly uncontrollable exothermic reactions caused by internal short circuits. The basic process of thermal runaway is divided into three stages. By analyzing the three characteristic temperatures and heating rate, it is proved that improving the thermal stability of electrolyte and seperator can alleviate thermal runaway. Then we investigated the influence of thermodynamics on the nucleation and growth of lithium dendrites, revealing the dual effects of temperature, and proving that a uniform thermal field is beneficial to obtain uniform lithium deposition and improve battery cycle performance and safety. Secondly, a variety of strategies to improve battery thermal safety are reviewed at the material level. In terms of liquid electrolytes, the development of non-flammable electrolyte systems includes the use of flame-retardant electrolytes and ionic liquid electrolytes with lower flammability. In addition, high-concentration electrolyte and local high-concentration electrolyte can change the solvation structure of lithium ions, and improve safety by reducing the number of free solvent molecules. In terms of separators, high thermal stability separators and thermal response separators with thermal shutdown function have been developed. The flame-retardant separators can release flame retardants to inhibit combustion. In addition, the new intelligent separators have dendrite detection, early warning and elimination functions, which effectively improve the safety and cycle life of the battery. In terms of solid electrolytes, thermally responsive polymer electrolytes have been developed to avoid thermal runaway through the strain function of polymer materials. Finally, further research on the thermal runaway of lithium metal batteries in the future is prospected.

Tin oxide (SnO₂) thin films are widely used as electron transport layers in planar perovskite solar cells (PSCs) and commonly prepared using solution-processed spin-coating. However, obtaining full coverage and pinhole-free surfaces for the spin-coated (SC) SnO₂ is challenging because the nanocrystals in the precursor solution can undergo aggregation, wherein the precursor solution may contain dust particles, and the desired film thickness is rater small. Since dense electron transport layer films without pinholes are crucial in suppressing the non-radiative recombination of charge carriers in PSCs, developing deposition methods to prepare high-quality SnO₂ films is important to improve the performance of planar PSCs. In this study, we investigated the application of electrophoresis (EP) in depositing compact and pinhole-free SnO₂ thin films. We conducted electrophoresis to deposit a dense nanocrystalline film on the surface of Indium tin oxide (ITO) and employed a spin-coating step to adjust the thickness of the film and remove the residual SnO₂ nanocrystalline precursor solution. This method was denoted as EP-SC. In the electrophoresis, the negatively charged SnO₂ nanocrystals, caused by a strong electric field, migrated towards the surface of the ITO anode and formed more compactly packed thin films than that of the spin-coated SnO₂. The atomic force microscopy (AFM) measurements demonstrated that the surface of EP-SC SnO₂ was more uniform than that of SC SnO₂ and there were no streaks and aggregated particles on the surface. This may have been due to the fact that the surface charge properties of the aggregated and dust particles in the precursor solution was different from that of the desired SnO₂ nanocrystals. Hence, electrophoresis can selectively deposit SnO₂ nanocrystals. Specifically, high-quality perovskites and electron transport layer interfaces can be achieved using this method. Both the electrochemical impedance spectroscopy (EIS) and dark J–V measurements showed that the PSCs using SnO₂ prepared by electrophoresis followed by spin-coating demonstrated remarkably suppressed non-radiative recombination. As a result, the photoelectric power conversion efficiency increased from 18.17% (based on SC) to 19.52% (based on EP-SC) due to the enhanced short-circuit current and open-circuit voltage. The hysteresis of the device was eliminated. More importantly, the long-term stability measurements demonstrated that our device can maintain up to 71% of the initial efficiency after 960 h of continuous operation at the maximum power point (MPP) under one sun illumination. Whereas the device based on spin-coated SnO₂ can maintain only up to 70% of the initial efficiency after working for 100 h. The results of this study can help in preparing electron transport layers to construct long-term stable planar PSCs, which are favorable for fabricating large-area PSCs and modules in future researches.

In addition to their extensive commercial application in electronic devices such as cell phones and laptops, lithium-ion batteries (LIBs) are most suitable to fulfill the energy storage requirements of electric vehicles because of their recognized safety, portability, and high energy density. Cathodes are the most important part of LIBs, and various cathode materials have been widely investigated over the past decades. Polaron formation has been attracting increasing attention in the research of cathode materials, as it limits electron conduction. In particular, polarons are responsible for low electronic conductivity in cathode materials like olivine phosphate. Polaron is a typical crystal defect caused by the integrated motion of lattice distortion and its trapping electrons. Research on the mechanism of polaron formation will provide theoretical guidance for the design of high-electronic-conductivity cathode materials and improvement of the electrochemical performance of LIBs. Theoretical calculation is a direct and important method to study polaron formation in a specific crystal material, because the presence of polarons and their formation mechanisms can be effectively verified through this method. In this article, we first introduce the basic physical concept of polarons and their dynamical model according to the Marcus and Emin-Holstein-Austin-Mott theories. A comparison of the general properties of large and small polarons, summarized in this chapter, reveals that small polaron formation more likely occurs in cathode materials. Moreover, the theoretical characterization, electrical impact, control and challenges of polarons are reviewed. Although a universal necessary and suitable condition for the theoretical characterization of polarons has not yet been found, we still propose three criteria that are proven to be feasible and practical for the theoretical identification of polarons when applied in combination. Experimental characterizations are also introduced briefly for reference, because the comparison with the experiment is suggested to be necessary and mandatory. The electrical impact caused by polarons results in low electronic conductivity, which has been broadly reported in layered, olivine, and spinel cathode materials. Doping can weaken the influence of polarons and, thus, significantly enhance the electronic conductivity, thereby becoming the most prevalent strategy for tuning polarons. Although theoretical calculations have been widely and effectively conducted in the study of polarons, some challenges may still be faced because of the intrinsic shortcomings of the traditional density functional theory, which need to be addressed. Finally, further research on polarons from the perspective of basic theory and practical applications is prospected.

In this work, light-responsive viscoelastic wormlike micelles based on cetyltrimethylammonium hydroxide (CTAOH) and cinnamic acid derivatives, including cinnamic acid (CA), 2-methoxycinnamic acid (2-MCA), 3-methoxycinnamic acid (3-MCA), 4-methoxycinnamic acid (4-MCA), 2, 3-dimethoxycinnamic acid (2, 3-DMCA), 2, 4-dimethoxycinnamic acid (2, 4-DMCA), 2, 3, 4-trimethoxycinnamic acid (2, 3, 4-DMCA), and 3, 4, 5-trimethoxycinnamic acid (3, 4, 5-DMCA), were prepared. The effects of the CA derivative structures, especially the position and number of methoxy moieties, on the formation of wormlike micelles were systematically determined. The CA derivatives facilitated the formation of long and entangled wormlike micelles. ¹H NMR results showed that the CA derivatives participated in the formation of wormlike micelles via insertion of the aromatic moieties into the aggregates. The number of methoxy moieties had a much stronger effect on the viscosity of the wormlike micelle solution than the position of this moiety. The larger the number of methoxy moiety, the smaller was the aggregate. Substituted methoxy moieties increased the steric hindrance between the surfactants and CA molecules, thus hindering the formation of large aggregates. However, the position of the methoxy moiety had a predominant effect on the UV-light-induced transition of the wormlike micelles. Specifically, the ortho-methoxy moiety in the CA molecules dramatically enhanced the efficiency of UV-light-induced trans-cis isomerization. For example, the 2-MCA/CTAOH, 3-MCA/CTAOH, and 4-MCA/CTAOH binary systems (90 mmol·L^-1/100 mmol·L^-1) were gel-like with similar viscosities of around 20 Pa·s, but after UV light irradiation, they were transformed into a fluid with lower viscosity because of the formation of smaller aggregates. However, the irradiation time required for the transition varied significantly, as suggested by the results of viscosity measurements and UV-Vis spectroscopy. The 2-MCA/CTAOH system underwent complete phase transition within 3 h, whereas continuous transitions were observed for the 3-MCA/CTAOH and 4-MCA/CTAOH systems upon irradiation for 24 h. ¹H NMR results suggested that the change in the configuration of MCA in the micelles before and after irradiation was the major cause of the abovementioned difference in the phase transition pattern. Initially, all the aromatic moieties of the trans-2-MCA molecules were deeply inserted into the hydrophobic cores of the micelles in a vertical manner, and the ionized carboxyl moiety was located in the palisade layer because of the electrostatic interactions between CTAOH and trans-2-MCA. In contrast, cis-2-MCA was inserted into the micelles in a horizontal manner, and some of the protons in the aromatic moiety were also transferred from the micellar core to the polar palisade layer. Accordingly, the CTAOH and cis-2-MCA molecules were packed loosely in the aggregates, thereby resulting in the formation of spherical micelles. Similar UV-light-induced transitions were observed for the 3-MCA/CTAOH and 4-MCA/CTAOH systems.

To fulfill the demands of green and sustainable energy, the production of novel catalysts for different energy conversion processes is critical. Owing to the intriguing advantages of the intrinsic active species, tunable crystal structure, remarkable chemical and physical properties, and good stability, metal-organic frameworks (MOFs) have been extensively investigated in various electrochemical energy conversions, such as the CO₂ reduction reaction, N₂ reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and oxygen reduction reaction. More importantly, it is feasible to change the chemical environments, pore sizes, and porosity of MOFs, which will theoretically facilitate the diffusion of reactants across the open porous networks, thereby improving the electrocatalytic performance. However, owing to the high energy barriers of charge transfer and limited free charge carriers, most MOFs show poor electrical conductivity, thus limiting their diverse applications. As reported previously, MOFs were used as a porous substrate to confine the growth of nanoparticles or co-doped electrocatalysts after annealing. The conductive MOFs can combine the advantages of conventional MOFs with electronic conductivity, which significantly enhance the electrocatalytic performance. In addition, conductive MOFs can achieve conductivity via electronic or ionic routes without post-annealing treatment, thereby extending their potential applications. Different synthesis strategies have recently been developed to endow MOFs with electrical conductivity, such as post-synthesis modification, guest molecule introduction, and composite formatting. The performance of conductive MOFs can even outperform those of commercial RuO₂ catalysts or Pt-group catalysts. However, it is difficult to endow most MOFs with high conductivity. This review summarizes the mechanisms of constructing conductive MOFs, such as redox hopping, through-bond pathways, through-space pathways, extended conjugation, and guest-promoted transport. Synthetic methods, including hydro/solvothermal synthesis and interface-assisted synthesis, are introduced. Recent advances in the use of conductive MOFs as heterogeneous catalysts in electrocatalysis have been comprehensively elucidated. It has been reported that conductive MOFs can demonstrate considerable catalytic activity, selectivity, and stability in different electrochemical reactions, revealing the immense potential for future displacement of Pt-group catalysts. Finally, the challenges and opportunities of conductive MOFs in electrocatalysis are discussed. Based on systematic synthesis strategies, more conductive MOFs can be constructed for electrocatalytic reactions. In addition, the morphology and structure of conductive MOFs, which can change the electrochemical accessibility between substrates and MOFs, are also crucial for catalysis, and thus, they should be extensively studied in the future. It is believed that a breakthrough for high-performance conductive MOF-based electrocatalysts could be achieved.

Perovskite solar cells (PSCs) have recently become one of the fastest-growing research fields. Furthermore, the PSCs that have a SnO₂ nanoparticle layer as an electron transport layer (ETL) have received extensive attention. The SnO₂-ETL layer can be prepared at a low temperature, which makes it suitable for flexible device development. However, the energy levels of the SnO₂ layer do not sufficiently match the energy levels of the perovskite light-absorbing layer, which largely affects the charge carrier extraction and reduces the open current–voltage (V_oc) of PSCs. Additionally, the interface between the ETL and perovskite layer always has defects, which cause charge recombination and affect the power conversion efficiency (PCE) of PSCs. Therefore, the interfacial engineering at the SnO₂/perovskite layer is crucial to address these issues. Researchers are looking for suitable passivation materials that could align the energy band and decrease the defect density. Halide materials, such as KCl and NH₄Cl, are promising solutions to solve these problems. However, the preparation process has to be explored, and the mechanism of halide ions at the interface is unclear. This study investigates the effects of SnO₂ surface halogenation on the photovoltaic performance of PSCs in depth. The SnO₂ surface was passivated using tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB), and tetrabutylammonium iodide (TBAI) and the concentration gradient of the passivation solution was studied. Extensive characterization of the perovskite layers and PSC devices demonstrated the positive effects of SnO₂ surface halogenation on the SnO₂/perovskite interfacial properties. The causes of improved performance of the interfacial-engineered devices were studied using charge carrier dynamics. Interfacial engineering was further investigated by performing first-principles calculations based on density functional theory (DFT) to determine the energy, structure, charge density, density of states, work function, etc. Experiments and theoretical calculations proved that TBAC could be an optimal passivation material for the SnO₂ surface. Furthermore, the passivation effect became more apparent with the increase in solution concentration. TBAC could promote perovskite crystal growth, decrease defects at the interface, and increase the internal recombination resistance. Consequently, the photovoltaic performance of PSCs was improved. The halide ions on the SnO₂ surface could interact with Sn atoms, which increase the charge density and achieves high-efficiency charge extraction. This work shows the significance of improving the photovoltaic performance of PSCs along with providing physical principles for the interfacial engineering of PSCs toward achieving high efficiency.

At present, more than 80% of the world's energy demand is fulfilled by the burning of fossil fuels, which has caused the production of a large amount of greenhouse gases, leading to global warming and damage to the environment. The high consumption of fossil fuels every year causes the energy crisis to become increasingly serious. Finding a sustainable and pollution-free energy source is therefore essential. Among all forms of energy sources, solar energy is preferred because of its cleanliness and inexhaustible availability. The energy provided by one year of sunlight is more than 100 times the total energy in known fossil fuel reserves worldwide; however, the extent of solar energy currently used by mankind each year is minute; thus developments in solar energy are imperative. To address the urgent need for a renewable energy supply and to solve environmental problems, a variety of technologies in the field of photocatalysis have been developed. Photocatalytic technology has attracted significant attention because of its superior ability to convert clean solar energy into chemical fuels. Among the photocatalytic materials emerging in an endless stream, perovskite oxide, with the general formula of ABO₃, has great potential in the fields of solar cells and photocatalysis as each site can be replaced by a variety of cations. Furthermore, owing to its unique properties such as high activity, robust stability, and facile structure adjustment, perovskite oxide photocatalysts have been widely used in water decomposition, carbon dioxide reduction and conversion, and nitrogen fixation. In terms of carbon dioxide reduction, oxide perovskites can achieve precise band gap and band edge tuning owing to its long charge diffusion length and flexibility in composition. For the development and utilization of solar energy in the environmental field, perovskite oxide and its derivatives (layered perovskite oxide) are used as photocatalysts for water decomposition and environmental remediation. In terms of nitrogen fixation, the conventional Haber-Bosh process for ammonia synthesis, which has been widely used in the past, requires high temperature and high energy. Therefore, we summarize the recent advances in perovskite oxide photocatalysts for nitrogen fixation from the aspect of activating the adsorbed N₂ by weakening the N $ \equiv $ N triple bond, promoting charge separation, and accelerating the charge transfer to the active sites to realize the photochemical reaction. Overall, this review article presents the structure and synthesis of perovskite oxide photocatalysis, focusing on the application of photocatalysis in water splitting, carbon dioxide reduction, and nitrogen fixation. This review concludes by presenting the current challenges and future prospects of perovskite oxide photocatalysts.

Molecular electronics is an important field for the application of nanotechnologies with an ultimate goal of building functional devices using single molecules or molecular arrays to realize the same functionality as macroscopic devices. To attain this goal, reliable techniques for measuring and manipulating electron transfer processes through single molecules are essential. There are various techniques and many environmental factors influencing single-molecule electronic conductance measurements. In this review, we first provide a detailed introduction and classification of the current well-accepted techniques in this field for measuring single-molecule conductance. All available techniques are summarized into two categories: the fixed junction technique and break junction technique. The break junction technique involves repeatedly forming and breaking molecular junctions by mechanically controlling a pair of electrodes moving into and out of contact in the presence of target molecules. Single-molecule conductance can be determined from the conductance plateaus that appear in typical conductance decay traces when molecules bind two electrodes during their separation process. In contrast, the fixed junction technique is to fix the distance between a pair of electrodes and measure the conductance fluctuations when a single molecule binds the two electrodes stochastically. Both techniques comprise different application methods and have been employed preferentially by different groups. Specific features of both techniques and their intrinsic advantages are compared and summarized in Section 4.

Next, we systematically summarize the factors affecting the molecular conductance during the course of measurements, which are the focus of the current academic community in the field. As shown in the middle of the image above, the electrode, anchoring group, and target molecule are the three key elements in constructing a single-molecule junction. The contact geometry between the molecule and the electrode and the associated coupling strength can profoundly affect the conductance characteristics of single molecules. The properties of anchoring groups can determine whether a molecule is primarily transported by electrons or holes. A good selection of electrode materials can improve the yield of single-molecule junctions and facilitate strong electronic couplings with the target molecules. The conductance characteristics of saturated and conjugated molecules are quite different due to their diverse band gaps. Moreover, various substituents can be modified onto the backbone of the molecules, which can raise or lower the energy level of the frontier orbitals of molecules to different degrees, thereby affecting the conductance properties of target molecules. In addition to these factors for the key elements, the investigated molecules can be measured in a variety of environments, including organic solvents, high vacuum, aqueous solution, ionic liquids, or the atmosphere, and the work function of the metal contact may change in different environments. The change in work function can change the gap between the electrode Fermi energy and the frontier orbital of a target molecule, influencing the measured conductance. Additionally, both the electrical field orientation and the bias values applied have a significant effect on the molecular structures and thus their conductance characteristics. Temperature can also affect the charge transport when hopping dominates the transport mechanism. Meanwhile, pH affects the interactions between H⁺/OH^- and the anchoring groups, which indirectly induces a change in the tunneling barrier.

In this review, the influencing factors are comprehensively illustrated from two perspectives: internal factors (anchoring group, electrode, and target molecule) and external factors (voltage, temperature, solvent, pH value, and others). In addition, new approaches for modulating the molecular conductance (modulation of energy levels, light or heat stimulation, and others) that have been developed in recent years are reviewed, and investigations of chemical reactions at the single-molecule level using these methods are highlighted. Finally, the potential applications of these techniques and correlated modulating approaches are summarized and a prospective is provided for the field of single-molecule electronics.

Industrial revolution has led to increased combustion of fossil fuels. Consequently, large amounts of CO₂ are emitted to the atmosphere, throwing the carbon cycle out of balance. Currently, the most effective method to reduce the CO₂ concentration is direct CO₂ capture from the atmosphere and pumping of the captured CO₂ deep underground or into the mid-ocean. The transformation of CO₂ into high-value chemicals is an attractive yet challenging task. In recent years, there has been much interest in the development of CO₂ utilization technologies based on electrochemical CO₂ reduction, photochemical CO₂ reduction, and thermal CO₂ reduction, and CO₂ valorization has emerged as a hot research topic. In electrochemical CO₂ reduction, the cathodic reaction is the reduction of CO₂ to value-added chemicals. The anodic reaction should be the oxygen evolution reaction, and water is the only renewable and scalable source of electrons and protons in this reaction. There is a plethora of research on the use of various metals to catalyze this reaction. Among these, Cu-based materials have been demonstrated to show unique catalytic activity and stability for the electrochemical conversion of CO₂ to valuable fuels and chemicals. Moreover, the solar-driven conversion of CO₂ into value-added chemical fuels has attracted great attention, and much effort is being devoted to develop novel catalysts for the photoreduction of CO₂, especially by mimicking the natural photosynthetic process. The key step in the photocatalytic process is the efficient generation of electron-hole pairs and separation of these charge carriers. The efficient separation of photoinduced charge carriers plays a crucial role in the final catalytic activity. Compared with CO₂ reduction via electrocatalysis and photocatalysis, thermal reduction is more attractive because of its potential large-scale application in the industry. Heterogeneous nanomaterials show excellent activity in the electrocatalytic, photocatalytic, and thermal catalytic conversion of CO₂. However, nanostructured materials have drawbacks on the investigation of the intrinsic activity of the active sites. In recent years, single-site catalysts have become popular because they allow for maximum utilization of the metal centers, show specific catalytic performance, and facilitate easy elucidation of the catalytic mechanism at the molecular level. Accordingly, numerous single-site catalysts were developed for CO₂ reduction to produce value-added chemicals such as CO, CH₄, CH₃OH, formate, and C₂₊ products. Value-added chemicals have also been synthesized with the aid of amines and epoxides. This review summarizes recent state-of-the-art single-site catalysts and their application as heterogeneous catalysts for the electroreduction, photoreduction, and thermal reduction of CO₂. In the discussion, we will highlight the structure-activity relationships for the catalytic conversion of CO₂ with single-site catalysts.

Although traditional graphite anodes ensure the cycling stability and safety of lithium-ion batteries, the inherent drawbacks, particularly low theoretical specific capacity (372 mAh·g^-1) and Li-free character, of such anodes limit their applications in high energy density battery systems, especially in lithium-sulfur and lithium-air batteries. Lithium metal has been considered as one of the best next-generation anode materials due to its extremely high theoretical specific capacity (3860 mAh·g^-1) and low redox potential (-3.04 V vs. the standard hydrogen electrode). The first generation of commercial rechargeable lithium metal batteries were developed by Moli Energy in the late 1980s and were not widely used due to several problems, including low coulombic efficiency, poor cycle stability, and safety hazards. These problems associated with the Li metal anode are mainly caused by lithium dendrite growth, electrode volume changes, and interface instability. During the charge and discharge processes, Li deposition is not uniform across the electrode surface. Due to the low surface energy and high migration energy of Li metal, dendrites are preferentially formed during Li deposition. These dendrites proceed to grow with successive battery cycling, penetrate the separator, and eventually reach the cathode, thereby causing short circuits and thermal runaway. Additionally, the growth of the lithium dendrite is inherently correlated with the reaction interface structure, and dendrite growth results in inhomogeneity of the SEI (solid electrolyte interface) which is inevitably formed on the Li metal surfaces. Moreover, the volume change of lithium metal anodes is of importance, particularly during battery cycling and Li stripping/deposition processes which make the SEI layers considerably unstable. SEI layers usually cannot withstand the mechanical deformation caused by volume changes; such layers continuously break and repair during cycling and consume large amounts of the electrolyte. Additionally, some Li dendrites could break and become wrapped by SEI layers to form electrically isolated "dead" Li, which results in the loss of active Li in the Li metal anode. All these factors are responsible for the failure of Li metal anodes. Herein, recent investigations on the failure mechanisms of lithium metal anodes are reviewed and summarized, including the formation of SEI layers on the surface of Li metal anodes, the behavior and mechanism of lithium dendrite growth, and the mechanism of "dead" lithium formation. Additionally, some advanced characterization techniques for investigating lithium metal anodes are introduced, including in situ tools, cryo-electron microscopy, neutron depth analysis technology, and solid state nuclear magnetic resonance technology. These techniques enable researchers to gain in-depth insights into the failure mechanisms of Li metal anodes.

Organic-inorganic hybrid lead halide perovskites have emerged as the most promising materials in the field of optoelectronics due to their unique electronic and optical properties. However, the poor long-term material and device stabilities of these materials have limited their practical application. Compared to organic-inorganic hybrid perovskites, all-inorganic halide perovskites like CsPbX₃ (X = Cl, Br, I) show enhanced thermal stability and the potential to resolve the issue of instability. Nevertheless, the structural and physical properties of all-inorganic CsPbX₃ halide perovskites with multiple structural polymorphs are still under debate. A recent research article on CsPbI₃ reported the wrongly indexed the XRD pattern of γ-CsPbI₃ as α-CsPbI₃. Consequently, the band gap of γ-CsPbI₃ (1.73 eV) was erroneously designated for α-CsPbI₃. Therefore, there is a need for systematic research on the relationship between the structural features and electronic properties of CsPbX₃. Here, we present a comprehensive theoretical study of the structural, thermodynamical and electronic properties of three polymorphic phases, α-, β-, and γ-CsPbX₃. The space group of α-, β-, and γ-CsPbX₃ are Pm${\rm{\bar 3}}$m, P4/mbm, and Pnma, respectively. First-principles calculations indicate that the phase transition from the high-temperature α-phase to the low-temperature β-phase and then to the γ phase is accompanied by an increase in the degree of PbX₆ octahedral distortion. The zero-temperature energetic calculations reveal that the γ-phase is the most stable. This is consistent with the fact that experimentally, the γ-phase is stabilized at a relatively low temperature. Analysis of the electronic properties indicates that all the CsPbX₃ perovskites exhibit a direct-gap nature and the band gap values increase from α to β, and then to the γ phase. From the analysis of the orbital hybridization near the band gap edges, the increase can be explained by the downshift of the valence band edges caused by the gradual weakening of the Pb-X chemical bond. Among all the phases, the strongest Pb-X interaction in the α-phase leads to the most dispersive band-edge states and thus the smallest carrier effective masses, which are beneficial for carrier transport. Additionally, the band gaps decreased by changing the halogen type from Cl to Br and I under the same phase. this is a consequence of the increased X np orbital energies from Cl 3p to Br 4p and then to I 3p that leads to a high valence band edge for CsPbI₃ and results in the smallest band gap. Our results provide deep understanding on the relationship between the physical properties and structural features of all-inorganic lead halide perovskites.

The self-assembly of colloidal nanocrystals has emerged as a powerful strategy for the bottom-up fabrication of functional materials and nanodevices. Recently, the self-assembly of gold nanorods (GNRs) has attracted significant attention because of their unique plasmonic properties, but the realization of their adjustable self-assembly of GNRs through facile and effective approaches remains challenging. In this work, the controllable self-assembly of GNRs in aqueous solution was realized through the host-guest interactions of cyclodextrins (CDs) and the cetyltrimethylammonium bromide (CTAB) molecules adsorbed on the surface of the GNRs. The self-assembly of GNRs was readily achieved by the addition of aqueous α-CD solutions with varied concentrations into aqueous dispersions of CTAB-stabilized GNRs. At a relatively low α-CD concentration, slow aggregation of the GNRs occurred, resulting in their side-by-side assembly. This was revealed by the blue shift of the longitudinal surface plasmon resonance (LSPR) band in the absorption spectra and confirmed by transmission electron microscopy (TEM) observations. On the other hand, when a higher concentration of α-CD was added, fast aggregation of the GNRs occurred, resulting in their end-to-end assembly. This was revealed by the red shift in the LSPR band together with the TEM observations. If β-CD was employed instead of α-CD, the self-assembly of GNRs could also be induced, although a relatively higher concentration of β-CD was required to achieve the extent of aggregation similar to that induced by α-CD, indicating that the supramolecular host–guest interaction between CDs and the surfactant CTAB was crucial to the directed self-assembly of GNRs. Furthermore, the α-CD-induced assembly was inhibited on addition of excess CTAB, confirming that the supramolecular interaction of α-CD and CTAB played a key role in directing the self-assembly of the GNRs. Based on these experimental results, a possible mechanism for the α-CD-induced self-assembly of GNRs was proposed as follows: at a lower α-CD concentration, the gradual formation of the host-guest inclusion complex α-CD/CTAB led to the partial replacement of the highly charged CTAB bilayers adsorbed on the GNRs by the less charged complex, which resulted in a slow side-by-side assembly of the GNRs; at a higher α-CD concentration, the CTAB bilayers were quickly replaced by the α-CD/CTAB complex, and the CTAB molecules adsorbed at both ends of the GNRs were almost completely replaced, resulting in a fast end-to-end assembly of the GNRs. Additionally, on the basis of the hydrolysis of α-cyclodextrin catalyzed by α-amylase, the self-assembly of GNRs directed by the host-guest interaction could be used to realize the feasible detection of α-amylase in solutions. This self-assembly strategy mediated by the host-guest interaction may be extendable to other colloidal systems involving surfactants adsorbed on the surface of nanoparticles, and may open new avenues for the controllable self-assembly of non-spherical nanoparticles.

Natural gas hydrates are considered as ideal alternative energy resources for the future, and the relevant basic and applied research has become more attractive in recent years. The influence of guest molecules on the hydrate crystal lattice parameters is of great significances to the understanding of hydrate structural characteristics, hydrate formation/decomposition mechanisms, and phase stability behaviors. In this study, we test a series of artificial hydrate samples containing different guest molecules (e.g. methane, ethane, propane, iso-butane, carbon dioxide, tetrahydrofuran, methane + 2, 2-dimethylbutane, and methane + methyl cyclohexane) by a low-temperature powder X-ray diffraction (PXRD). Results show that PXRD effectively elucidates structural characteristics of the natural gas hydrate samples, including crystal lattice parameters and structure types. The relationships between guest molecule sizes and crystal lattice parameters reveal that different guest molecules have different controlling behaviors on the hydrate types and crystal lattice constants. First, a positive correlation between the lattice constants and the van der Waals diameters of homologous hydrocarbon gases was observed in the single-guest-component hydrates. Small hydrocarbon homologous gases, such as methane and ethane, tended to form sI hydrates, whereas relatively larger molecules, such as propane and iso-butane, generated sⅡ hydrates. The hydrate crystal lattice constants increased with increasing guest molecule size. The types of hydrates composed of oxygen-containing guest molecules (such as CO₂ and THF) were also controlled by the van der Waals diameters. However, no positive correlation between the lattice constants and the van der Waals diameters of guest molecules in hydrocarbon hydrates was observed for CO₂ hydrate and THF hydrate, probably due to the special interactions between the guest oxygen atoms and hydrate "cages". Furthermore, the influences of the macromolecules and auxiliary small molecules on the lengths of the different crystal axes of the sH hydrates showed inverse trends. Compared to the methane + 2, 2-dimethylbutane hydrate sample, the length of the a-axis direction of the methane + methyl cyclohexane hydrate sample was slightly smaller, whereas the length of the c-axis direction was slightly longer. The crystal a-axis length of the sH hydrate sample formed with nitrogen molecules was slightly longer, whereas the c-axis was shorter than that of the methane + 2, 2-dimethylbutane hydrate sample at the same temperature.

Cu/ZrO₂ catalysts have demonstrated effective in hydrogenation of CO₂ to methanol, during which the Cu-ZrO₂ interface plays a key role. Thus, maximizing the number of Cu-ZrO₂ interface active sites is an effective strategy to develop ideal catalysts. This can be achieved by controlling the active metal size and employing porous supports. Metal-organic frameworks (MOFs) are valid candidates because of their rich, open-framework structures and tunable compositions. UiO-66 is a rigid metal-organic skeleton material with excellent hydrothermal and chemical stability that comprises Zr as the metal center and terephthalic acid (H₂BDC) as the organic ligand. Herein, porous UiO-66 was chosen as the ZrO₂ precursor, which can confine Cu nanoparticles within its pores/defects. As a result, we constructed a Cu-ZrO₂ nanocomposite catalyst with high activity for CO₂ hydrogenation to methanol. Many active interfaces could form when the catalysts were calcined at a moderate temperature, and the active interface was optimized by adjusting the calcination temperature and active metal size. Furthermore, the Cu-ZrO₂ interface remained after CO₂ hydrogenation to methanol, as confirmed by transmission electron microscopy (TEM), demonstrating the stability of the active interface. The catalyst structure and hydrogenation activity were influenced by the content of the active component and the calcination temperature; therefore, these parameters were explored to obtain an optimized catalyst. At 280 ℃ and 4.5 MPa, the optimized CZ-0.5-400 catalyst gave the highest methanol turnover frequency (TOF) of 13.4 h^-1 with a methanol space-time yield (STY) of 587.8 g·kg^-1·h^-1 (calculated per kilogram of catalyst, the same below), a CO₂ conversion of 12.6%, and a methanol selectivity of 62.4%. In situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption over the optimized catalyst revealed a predominant, unreducible Cu⁺ species that was also identified by X-ray photoelectron spectroscopy (XPS). The favorable activity observed was due to this abundant Cu⁺ species coming from the Cu⁺-ZrO₂ interface that served as the methanol synthesis active center and acted as a bridge for transporting hydrogen from the active Cu species to ZrO₂. In addition, the oxygen vacancies of ZrO₂ promoted the adsorption and activation of CO₂. These vacancies and Cu⁺ trapped in the ZrO₂ lattice are the active sites for methanol synthesis from CO₂ hydrogenation. The X-ray diffraction (XRD) patterns of the catalyst before and after reaction revealed the stability of its structure, which was further verified by time-on-stream (TOS) tests. Furthermore, in situ DRIFTS and temperature-programmed surface reaction-mass spectroscopy (TPSR-MS) revealed the reaction mechanism of CO₂ hydrogenation to methanol, which followed an HCOO-intermediated pathway.

Visible-blind ultra-violet (UV) photodetectors have great application prospects in military and civilian fields. Hence, it is important to develop high-efficiency UV photodetectors. Perovskite materials have been widely applied in many fields, such as solar cells, light-emitting diodes, and photodetectors, owing to their excellent optical properties. The CsPbCl₃ perovskite has a great potential in visible-blind UV photodetectors owing to its stable chemical properties and a suitable band gap. However, due to the extremely poor precursor solubility of CsPbCl₃, it is difficult to find a suitable solvent to prepare CsPbCl₃ films. In this study, we developed a two-step diffusion method to prepare CsPbCl₃ films. PbCl₂ and CsCl were dissolved in different solvents to overcome the solubility problem of CsPbCl₃. First, the PbCl₂ film was spin coated on a soda-lime glass. The CsCl solution was then continually dropwise spin-coated on the PbCl₂ film to form the CsPbCl₃ film. By controlling the morphology of PbCl₂ through different annealing temperatures, the influence of different PbCl₂ precursor films on microstructure of the CsPbCl₃ film was investigated. The X-ray diffraction and scanning electron microscopy profiles of the PbCl₂ precursor film and the CsPbCl₃ film suggested that when the annealing temperature was too low, excess dimethyl sulfoxide (DMSO) remained in the PbCl₂ precursor film, which hindered the transformation of CsPbCl₃. However, when the annealing temperature was too high, voids appeared in the CsPbCl₃ film due to excess DMSO volatilization, which caused pinholes in the CsPbCl₃ film. Finally, a pinhole-free, smooth CsPbCl₃ film with full grains was obtained when PbCl₂ was annealed at 80 ℃. To the best of our knowledge, this is the first time a high-quality CsPbCl₃ film with 1 μm grains was prepared using a two-step diffusion method. Photoelectrical characterizations, such as ultraviolet-visible absorption, steady-state photoluminescence (PL), and time-resolved PL characterizations, were studied to evaluate the quality of the film. The as-prepared CsPbCl₃ film had strong UV absorption and PL intensity, and its longer PL lifetime indicated that the film had fewer defect states. Furthermore, a UV photodetector with a lateral structure based on the CsPbCl₃ film was fabricated. The related electrical characterizations, such as current voltage curves, showed a good responsivity of 0.75 A·W^-1 and an outstanding detectivity of 7.8 × 10¹² Jones, which are better than those of contemporary commercial photodetectors. The findings of this study show that a two-step diffusion method can be used to prepare CsPbCl₃ films with better features and that it has a great potential in the development of UV photodetectors in the future.

With the booming growth market of electric vehicles and portable electronics, high-energy-density rechargeable lithium ion batteries are being extensively used to advance high-end devices. Lithium-ion batteries with graphite anodes approach the ceiling in energy density, but they cannot satisfy the current demand. Among the next-generation electrodes, lithium metal anodes are strong candidates because of their high theoretical capacity and the most negative electrochemical potential. However, lithium metal batteries have been abandoned because of their poor safety resulting from the growth of lithium dendrites during lithium deposition. Although several strategies have been proposed to suppress the generation of lithium dendrites as well as the side reactions between active lithium and the electrolyte, lithium metal anodes have not been practically applied so far. Various studies have been conducted on the factors influencing lithium deposition, with the aim of understanding the growth behavior of lithium dendrites. The electrolyte plays a crucial role in the performance of the working Li metal anode. In this study, a unique battery system is proposed to realize columnar lithium deposition, which is convenient for obtaining the length and diameter of lithium deposits. The influence of different electrolytes on lithium deposition was investigated by comparing the length-diameter (L/D) ratio of the lithium deposits in two kinds of electrolytes (1.0 mol·L^-1 LiPF₆-ethylene carbonate/diethyl carbonate (EC/DEC, 1 : 1 by volume) and 1.0 mol·L^-1 LiPF₆-5% (volume fraction) fluoroethylene carbonate (FEC)-EC/DEC (1 : 1 by volume)). The morphology of the lithium deposits was strongly affected by the electrolyte composition. In the electrolyte with the FEC additive, the diameter of columnar lithium increased from 0.3-0.6 μm to 0.7-1.3 μm, while the L/D ratio decreased from 12.5 to 5.6. The small L/D ratio can reduce the reactive area between the lithium metal anode and the electrolyte, which is beneficial for achieving high lithium utilization and a long lifespan. To probe the origin of this influence, the surface chemistry of the cycled lithium metal anode was investigated by X-ray photoelectron spectroscopy. The FEC additive can increase the proportion of lithium fluoride (LiF) in the solid electrolyte interphase, which is conducive for the rapid diffusion of lithium ions. As a result, fewer nucleation sites are formed, providing more space for the growth of lithium cores with a large diameter. Therefore, the addition of FEC leads to a decrease in the L/D ratio of columnar lithium.

The radioactivity and toxicity of actinides impede experimental investigation into their chemical properties in the condensed phase. The rapid development of computational methods and computational facilities allows for alternative experimental methods, including the use of a molecular force field, to gain insight into the coordination chemistry and dynamics of actinides. The key to this method is the force fieild parameters. In the present work, we report the development and validation of the AMBER (Assisted Model Building with Energy Refinement) force field parameters for Np⁴⁺, Am³⁺, and Cm³⁺ based on the experimentally determined ion-oxygen distance (IOD). The parameter set, together with that reported for Th⁴⁺, U⁴⁺, and Pu⁴⁺, was then applied to investigate the coordination chemistry and dynamics of these six actinide ions in the aqueous phase, in the absence and presence of counterions Cl^-, NO₃^-, and CO₃^2-. The simulations showed a shorter An-O_w coordination length for An⁴⁺ than for An³⁺, and for higher atomic numbers of ions in the same valence state. Th⁴⁺ preferentially existed in a 10-coordinated state, adopting a BCASP (bicapped square antiprism) conformation, while the other ions tended to be 9-coordinated with a CASP (capped square antiprism) conformation. The only exception was Cm³⁺, which adopted a TCTP (tricapped trigonal prism) conformation. The results also showed that the water molecules around An⁴⁺ were more ordered than those around An³⁺, as indicated by the smaller angles between the An-O_w vector and the dipole direction of the water ligand. This highly ordered structure of coordinated water affected their translation and rotation, i.e., the diffusion coefficient and rotational relaxation time of the water molecules around An⁴⁺ were smaller than those in the case of An³⁺ due to the stronger electrostatic interaction between An⁴⁺ and ligating water. The hydration free energies of the targeted actinide ions were also calculated by the FEP (free energy perturbation) method. An⁴⁺ underwent a greater degree of stabilization than did An³⁺ upon hydration; among the ions in the same oxidation states, those with a higher atomic number were better stabilized. In summary, the results of the simulations were consistent with the literature data in terms of the hydration structure, coordination of counterions, and hydration free energy of the actinide ions. The ability of the parameter set to describe the dynamics of water in the vicinity of actinides remains to be verified due to the lack of reference data. We tentatively propose that it may be used to investigate the coordination chemistry of actinides both in conformational analysis and binding strength, while special care should be taken when studying the kinetics of the solvated system. This work is expected to enrich our understanding of the solution behavior of An³⁺/An⁴⁺ at the force field level.

Miscibility between oil and supercritical carbon dioxide (scCO₂) phases has attracted significant attention in the field of oil recovery because it can be utilized in miscible gas displacement of oil, achieving nearly 100% recovery efficiency. The high recovery efficiency of miscible CO₂ flooding originates from the valuable heavy components of oil and CO₂ gas phase forming a homogenous phase with high mobility in the oil-scCO₂ miscible system. However, the high pressure required for oil-scCO₂ miscibility is a nontrivial obstacle for practical applications of scCO₂ flooding recovery. Therefore, it is important to develop assist-miscible agents to lower the necessary miscibility pressure. In oil and water systems, well-developed amphiphiles (such as surfactants) have shown great promise for reducing the interfacial tension and maintaining the stability of the emulsion system. Therefore, "oil-CO₂ amphiphiles" that can assist the miscibility between oil and scCO₂ have been proposed. Among potential oil-scCO₂ amphiphiles, a series of polyester-based oil-CO₂ amphiphiles with esters as the CO₂-philic groups and long carbon chains as the oil-philic groups were prepared. The polyester-based oil-CO₂ amphiphiles, acting as assist-miscible agents, showed great ability to lower the needed miscibility pressure. A visualized miscible method was used to examine the efficiency of the assist-miscible agents with white oil and kerosene as the oil phase. The height of the oil phase inside the chamber was measured through a glass window to monitor the miscibility with increasing CO₂ pressure. When the height of the oil reached the top of chamber, the oil filled the entire space, indicating miscibility. Using this method, the following conclusions could be drawn: First, amphiphiles with more ester groups exhibited stronger CO₂-philicity, providing stronger ability to dissolve carbon dioxide. Second, amphiphiles with hydrocarbon chain lengths of 16 carbons exhibited the optimal assist-miscible efficiency. Third, greater differences between the oil and scCO₂ phase showed more obvious differentiation among amphiphiles, showing the leveling and differentiating effect of oil. The temperature range of 50–80 ℃ did not influence the assist-miscible efficiency of the polyester-based amphiphiles. The best miscibility-assisting performance was obtained with CAA8-X, which contains eight ester groups and a palmitic acid chain. CAA8-X at a concentration of 1% (w, mass fraction) lowered the miscibility pressure in the white oil-scCO₂ system by 16.04%. Amphiphiles with polyether (PEO) groups also showed excellent assist-miscible efficiency. The findings presented herein extend the concept of "amphiphilicity" from oil-water phases to oil-scCO₂ phases and have the potential to guide future studies regarding scCO₂ flooding in actual CO₂ flooding oil recovery. Moreover, for other two-phase systems, according to the general amphipathic law and particular system parameters, it should be possible to design the optimal "amphiphiles".

Since their commercialization in 1991, lithium-ion batteries (LIBs), one of the greatest inventions in history, have profoundly reshaped lifestyles owing to their high energy density, long lifespan, and reliable and safe operation. The ever-increasing use of portable electronics, electric vehicles, and large-scale energy storage has consistently promoted the development of LIBs with higher energy density, reliable and safe operation, faster charging, and lower cost. To meet these stringent requirements, researchers have developed advanced electrode materials and electrolytes, wherein the electrode materials play a key role in improving the energy density of the battery and electrolytes play an important role in enhancing the cycling stability of batteries. In addition, further improvements in the current LIBs and reviving lithium metal batteries have received intensive interest. The electrode/electrolyte interface is formed on the electrode surface during the initial charging/discharging stage, whose ionic conductivity and electronic insulation ensure rapid transport of lithium ions and isolating the unsolicited side reactions caused by electrons, respectively. In a working battery, the stability or properties of the interface play a crucial role in maintaining the integrity of the electrode structure, thereby stabilizing the cycling performance and prolonging the service lifespan to meet the sustainable energy demand for the public. Generally, the interface formed on the anode and cathode is called the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) respectively, and SEI and CEI are collectively known as the electrode electrolyte interphase. Research on SEI has made remarkable progress; however, the structure, component, and accurate regulation strategy of SEI are still at the initial stage due to the stability and complexity of SEI and the limited research methods at the nanoscale. To improve the performance and lifespan of working batteries, the formation, evolution, and modification of the interface should be paid particular attention. Herein, the latest researches focused on the SEI are reviewed, including the formation mechanism, which discusses two key factors affecting the formation of the electrode/electrolyte film, i.e., the ion characteristic adsorption on the electrode surface and the solvated coordinate structure, evolution, and description that contains the interface layer structure, wherein the mosaic model and the layered structure are the two mainstream views of the SEI structure, and the chemical composition of SEI as well as the possible conduction mechanism of lithium ions, including desolvation and subsequent diffusion across the polycrystalline SEI. The regulation strategies of the interface layer are discussed in detail, and the future prospects of SEI are presented.

Proton exchange membrane fuel cells (PEMFCs) have attracted significant attention owing to their high conversion efficiency, high power density, and low pollution. Their performance is mainly governed by the oxygen reduction reaction (ORR) occurring at the cathode. Owing to the sluggish kinetics of ORR, a large amount of electrocatalysts, i.e., platinum (Pt), is required to accelerate the reaction rate and improve the performance of PEMFCs for practical applications. The use of Pt electrocatalysts inevitably increases the cost, thereby hindering the commercialization of PEMFCs. In addition, the activity and stability of the commercial Pt/C catalyst are still insufficient. Therefore, advanced electrocatalysts with high activity, good stability, and low cost are urgently needed. To date, some theoretical models, especially d-band center theory, have been proposed and guided the search for next-generation electrocatalysts with higher ORR activity. Based on these theories, several strategies and catalysts, especially Pt-based alloy catalysts, have been developed to accelerate ORR and improve the fuel cell performance. For instance, Pt–Ni octahedral nanoparticles (NPs) electrocatalysts have achieved remarkable ORR activity, with one order of magnitude higher activity than that of commercial Pt/C. However, PEMFCs are usually operated at a high voltage (0.6–0.8 V) and an acidic electrolyte, where the transition metals (M) are easily oxidized and etched away. The electronic effect induced by the introduction of M would be eliminated due to the dissolution of transition metals and the agglomeration of NPs, leading to the decay of ORR activity. Therefore, the long-term stability of oxygen reduction catalysts and fuel cells remains highly challenging. It is crucial to design an efficient and highly stable ORR catalyst to promote the application of PEMFCs. Aiming to the stability issues of fuel cell cathode catalysts, the current review summarizes the principles, strategies, and approaches for improving the stability of Pt-based catalysts. First, we introduce thermodynamic and kinetic principles that affect the stability of catalysts. Thermodynamic (such as cohesive energy, alloy formation energy, and segregation energy) and kinetic parameters (such as vacancy formation and diffusion barrier) regarding the structural stability of catalysts significantly affect the metal dissolution and atomic diffusion processes. In addition, these parameters seem to be associated with chemical bond energy to some extent, which could be employed as a descriptor for the stability of catalysts. Later, we outline some representative strategies and methods for improving catalyst stability, namely elemental doping, atomic arrangement engineering, chemical or physical confinement, and supporting material design. Finally, a brief summary and future research perspectives are provided.

Optogenetics transforms specific types of neurons through genetic engineering to achieve the cell membrane expression of photosensitive channel protein. When a specific wavelength of light irradiates the photosensitive channel protein, the cell is either excited or inhibited. Optogenetics provides a precise and fast method to control the activity of individual neurons for neuroscience research, which has gained increasing attention as a means of neural regulation. To realize the photogenetic regulation of neurons, light should be introduced into the brain safely and efficiently. Thus, specialized photoelectric devices are needed. Optrode plays a significant role in the application of optogenetics tools, which is the technical basis for the application of optogenetics. Optrode is a kind of implantable neural interface device. It can introduce light into the brain to regulate neural activity and record the changes of neural electrical signals under the control of lights. As the research of optogenetic technology continues, More and more optrodes are being developed and applied in the study of neuroscience and diseases, such as neural circuit, cognition and memory, epilepsy, and sensory function damage. The combination of optrode with optogenetic technologies provides various developmental modes in terms of material selection, device structure, light supply method, and integrated ways. The difficulty in fabricating optrodes lies in performing light stimulation and electrical signal recording without causing the immune rejection of the test animal and affecting its normal physiological activities simultaneously. In this study, based on structural characteristics and manufacturing process, optrodes are classified into two categories: waveguide-based and micro-light emitting diode-based. Subsequently, based on manufacturing process and light supply method, waveguide-based optrodes are further divided into optical fiber-optrode, optical waveguide-optrode based on MENS technology, and LD/LED waveguide-optrode. Similarly, micro-light emitting diode-based optrodes are divided into hard μLED optrode and soft μLED optrode. The advantages and disadvantages of different types of optrodes, as well as the evolution direction, are reviewed and summarized. Additionally, problems with existing optrodes, such as signal quality, biocompatibility, and device reliability, are discussed. Further, the ideal form of the device is presented as possessing the following characteristics: μLED and recording electrode integrated on flexible substrate, small size, high spatial resolution, high biocompatibility, wireless energy supply, wireless data transmission, etc. As optrode technologies are continuously updated, in the application of optogenetic technologies, research on brain neural circuit and functional structure will be better studied, and various nerve diseases will be gradually tamed.

Photocatalytic reduction of carbon dioxide into chemical fuels is a promising route to generate renewable energy and curtail the greenhouse effect. Therefore, various photocatalysts have been intensively studied for this purpose. Among them, g-C₃N₄, a 2D metal-free semiconductor, has been a promising photocatalyst because of its unique properties, such as high chemical stability, suitable electronic structure, and facile preparation. However, pristine g-C₃N₄ suffers from low solar energy conversion efficiency, owing to its small specific surface area and extensive charge recombination. Therefore, designing g-C₃N₄ (CN) nanosheets with a large specific surface area is an effective strategy for enhancing the CO₂ reduction performance. Unfortunately, the performance of CN nanosheets remains moderate due to the aforementioned charge recombination. To counter this issue, loading a cocatalyst (especially a two-dimensional (2D) one) can enable effective electron migration and suppress electron-hole recombination during photo-irradiation. Herein, CN nanosheets with a large specific surface area (97 m²·g^-1) were synthesized by a two-step calcination method, using urea as the precursor. Following this, a 2D/2D FeNi-LDH/g-C₃N₄ hybrid photocatalyst was obtained by loading a FeNi layered double hydroxide (FeNi-LDH) cocatalyst onto CN nanosheets by a simple hydrothermal method. It was found that the production rate of methanol from photocatalytic CO₂ reduction over the FeNi-LDH/g-C₃N₄ composite is significantly higher than that of pristine CN. Following a series of characterization and analysis, it was demonstrated that the FeNi-LDH/g-C₃N₄ composite photocatalyst exhibited enhanced photo-absorption, which was ascribed to the excellent light absorption ability of FeNi-LDH. The CO₂ adsorption capacity of the FeNi-LDH/g-C₃N₄ hybrid photocatalyst improved, owing to the large specific surface area and alkaline nature of FeNi-LDH. More importantly, the introduction of FeNi-LDH on the CN nanosheet surface led to the formation of a 2D/2D heterojunction with a large contact area at the interface, which could promote the interfacial separation of charge carriers and effectively inhibit the recombination of the photogenerated electrons and holes. This subsequently resulted in the enhancement of the CO₂ photo-reduction activity. In addition, by altering the loading amount of FeNi-LDH for photocatalytic performance evaluation, it was found that the optimal loading amount was 4% (w, mass fraction), with a methanol production rate of 1.64 μmol·h^-1·g^-1 (approximately 6 times that of pure CN). This study provides an effective strategy to improve the photocatalytic CO₂ reduction activity of g-C₃N₄ by employing 2D layered double hydroxide as the cocatalyst. It also proposes a protocol for the successful design of 2D/2D photocatalysts for solar energy conversion.

As a powerful tool for monitoring and modulating neural activities, implantable neural electrodes constitute the basis for a wide range of applications, including fundamental studies of brain circuits and functions, treatment of various neurological diseases, and realization of brain-machine interfaces. However, conventional neural electrodes have the issue of mechanical mismatch with soft neural tissues, which can result in tissue inflammation and gliosis, thus causing degradation of function over chronic implantation. Furthermore, implantable neural electrodes, especially depth electrodes, can only carry out limited data sampling within predefined anatomical regions, making it challenging to perform large-area brain mapping. With excellent electrical, mechanical, and chemical properties, carbon-based nanomaterials, including graphene and carbon nanotubes (CNTs), have been used as materials of implantable neural electrodes in recent years. Electrodes made from graphene and CNT fibers exhibit low electrochemical impedance, benefiting from the porous microstructure of the fibers. This enables a much smaller size of neural electrode. Together with the low Young's modulus of the fibers, this small size results in very soft electrodes. Soft neural electrodes made from graphene and CNT fibers show a much-reduced inflammatory response and enable stable chronic in vivo action potential recording for 4-5 months. Combining different modalities of neural interfacing, including electrophysiological measurement, optical imaging/stimulation, and magnetic resonance imaging (MRI), could leverage the spatial and temporal resolution advantages of different techniques, thus providing new insights into how neural circuits process information. Transparent neural electrode arrays made from graphene or CNTs enable simultaneous calcium imaging through the transparent electrodes, from which concurrent electrical recording is taken, thus providing complementary cellular information in addition to high-temporal-resolution electrical recording. Transparent neural electrodes from carbon-based nanomaterials can record well-defined neuronal response signals with negligible light-induced artifacts from cortical surfaces under optogenetic stimulation. Graphene and CNT-based materials were used to fabricate MRI-compatible neural electrodes with negligible artifacts under high field MRI. Simultaneous deep brain stimulation (DBS) and functional magnetic resonance imaging (fMRI) with graphene fiber electrodes in the subthalamic nucleus (STN) in Parkinsonian rats revealed robust blood oxygenation level dependent responses along the basal ganglia-thalamocortical network in a frequency-dependent manner, with responses from some regions not previously detectable. This review introduces the recent development and application of neural electrode technologies based on graphene and CNTs. We also discuss biological safety issues and challenges faced by neural electrodes made from carbon nanomaterials. The use of carbon-based nanomaterials for the fabrication of various soft and multi-modality compatible neural electrodes will provide a powerful platform for both fundamental and translational neuroscience research.

As one of the most promising hydrogen production technologies, electrochemical water splitting is an effective measure for solving environmental pollution and energy crises. However, the slow kinetics and high overpotential of the oxygen evolution reaction (OER) are the primary deterrents for improving the efficiency of water splitting devices. Iridium- and ruthenium-based noble metal catalysts are extremely expensive, which limits the industrial-scale development of this technology. Therefore, the development of oxygen evolution catalysts with high activity, excellent stability, and low costs is significantly important for water splitting technologies. Nickel-based materials meet the requirements of high abundance, cost-effectiveness, and high activity. In recent years, nickel-based metal organic frameworks (Ni-based MOFs) have attracted increasing research attention owing to their diverse and tunable topological structures and large specific surface areas. Furthermore, the mesoporous three-dimensional structure of MOFs can promote the diffusion of reactants, rendering them excellent candidates for catalytic applications. In order to utilize the advantages of Ni-MOFs more efficiently, the following methods are usually used to improve their catalytic performance. Owing to their unique properties, metal nodes can be replaced without affecting the MOF skeleton. As iron series metals, Co and Fe doping show unique catalytic activity and structural stability due to the synergistic effect between metal centers. Further, Ni-MOFs can simultaneously be used as precursors for oxidation, phosphating, or vulcanization to obtain Ni-MOF derivatives with different components. Among them, high-temperature carbonization treatment can make use of abundant organic ligands of Ni-MOFs to form a partially graphitized carbon-based framework, thereby augmenting conductivity, preventing the aggregation and corrosion of transition metals, and improving the overall support strength. The catalytic performance of oxygen production can be further improved by directly growing the Ni-MOFs on the substrate and introducing other active substances or conductive materials. Herein, the latest developments of Ni-based MOFs and their derivatives have been reviewed with regard to their utilization in OER catalysis, including nickel oxides, nickel hydroxides, nickel phosphides, nickel sulfides, and carbon composite materials. First, the mechanism and measurement criteria of the OER are briefly introduced. Second, the structures of several typical Ni-based MOFs (MOF-74, MILs, PBAs, and ZIFs) and their preparation methods are described. Subsequently, recent advances in the application of Ni-based MOFs and their derivatives in the OER are discussed, with an emphasis on materials design strategies and catalytic mechanisms. Finally, the main challenges and opportunities in this field are proposed.

In past decades, lithium-ion batteries (LIBs) were the dominant energy storage systems for powering portable electronic devices because of their reliable cyclability. However, further increase in the energy density of LIBs was met by a bottleneck when low-specific- capacity graphite was used at the anode. Li metal has long been regarded as the ideal anode material for building the next high-energy-density batteries due to its ultrahigh capacity of 3860 mAh·g^-1, which is ten times higher than that of graphite. However, using Li metal as an anode in rechargeable batteries is challenging due to its high uncontrolled volume expansion and aggressive side reactions with liquid electrolytes. In this study, we demonstrate the effect of a three-dimensional (3D) framework with enriched fluorinated sites for Li metal protection. This framework is obtained via a facile integration of down-sized fluorinated graphite (CF_x) particles into Li⁺ conducting channels. Thermogravimetry, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy results show that Li⁺ conducting channels rich in lithium fluoride (LiF) are formed in situ across the embedded CF_x particles during the initial lithiation process, leading to fast Li⁺ transfer. Scanning electron microscopy results show that residual CF_x particles could act as high-quality nucleation sites for uniform Li deposition inside the framework. These features could not be achieved with a 2D structure consisting of large CF_x flakes, due to the limited Li⁺ transfer paths and low utilization ratio of CF_x for conversion into LiF-based solid electrolyte interphase (SEI) layers. Consequently, better performance of Li metal anodes in a 3D framework with enriched fluorinated sites is demonstrated. Stable Li plating/stripping over 240 cycles is obtained at a current density of 0.5 mA·cm^-2 for a fixed capacity of 1 mAh·cm^-2 by maintaining a voltage hysteresis below 80 mV. Improved Li-LiFePO₄ full cell performance with a practical negative/positive capacity ratio of 3 is also demonstrated. These results show the rational combination of well-developed 3D Li⁺ transfer channels and enriched fluorinated sites as an optimized interfacial design beyond the single use of a 2D fluorinated interface, giving new insight into the protection of Li metal anodes in high-energy-density batteries.

Neural interfaces have contributed significantly to our understanding of brain functions as well as the development of neural prosthetics. An ideal neural interface should create a seamless and reliable link between the nervous system and external electronics for long periods of time. Implantable electronics that are capable of recording and stimulating neuronal activities have been widely applied for the study of neural circuits or the treatment of neurodegenerative diseases. However, the relatively large cross-sectional footprints of conventional electronics can cause acute tissue damage during implantation. In addition, the mechanical mismatch between conventional rigid electronics and soft brain tissue has been shown to induce chronic tissue inflammatory responses, leading to signal degradation during long-term studies. Thus, it is essential to develop new strategies to overcome these existing challenges and construct more stable neural interfaces. Owing to their unique physical and chemical properties, one-dimensional (1D) and two-dimensional (2D) nanomaterials constitute promising candidates for next-generation neural interfaces. In particular, novel electronics based on 1D and 2D nanomaterials, including carbon nanotubes (CNTs), silicon nanowires (SiNWs), and graphene (GR), have been demonstrated for neural interfaces with improved performance. This review discusses recent developments in neural interfaces enabled by 1D and 2D nanomaterials and their electronics. The ability of CNTs to promote neuronal growth and electrical activity has been proven, demonstrating the feasibility of using CNTs as conducting layers or as modifying layers for electronics. Owing to their good mechanical, electrical and biological properties, CNTs-based electronics have been demonstrated for neural recording and stimulation, neurotransmitter detection, and controlled drug release. Different from CNTs-based electronics, SiNWs-based field effect transistors (FETs) and microelectrode arrays have been successfully demonstrated for intracellular recording of action potentials through penetration into neural cells. Significantly, SiNWs FETs can detect neural activity at the level of individual axons and dendrites with a high signal-to-noise ratio. Their ability to record multiplexed intracellular signals renders SiNWs-based electronics superior to traditional intracellular recording techniques such as patch-clamp recording. Besides, SiNWs have been explored for optically controlled nongenetic neuromodulation due to their tunable electrical and optical properties. As the star of the 2D nanomaterials family, GR has been applied as biomimetic substrates for neural regeneration. Transparent GR-based electronics combining electrophysiological measurements, optogenetics, two-photon microscopy with multicellular calcium imaging have been applied for the construction of multimodal neural interfaces. Finally, we provide an overview of the challenges and future perspectives of nanomaterial-based neural interfaces.

Fuel cells have attracted much attention because of their high specific energy and low environmental load, but their commercial application is limited by the poor performance and high cost of the relevant electrode catalysts. The oxygen reduction reaction (ORR) is the key cathodic reaction in a fuel cell, and it plays an important role in the chemical energy conversion. However, the slow reaction kinetics, large reaction energy barrier, and low selectivity deteriorate the energy efficiency of fuel cells. Thus, rational design of low-cost electrocatalysts that show good activity is highly desirable for improving the performance of fuel cells. Although noble-metal-based electrocatalysts (e.g., Pt/C) show excellent catalytic activity for the ORR, their limited resources, high price, and low stability caused by the migration and agglomeration of nanoparticles on the surface of carbon supports have hindered their extensive application. Because of their excellent electrical conductivity and stability, carbon-based materials are widely used as substrates for electrode materials in the ORR. Heteroatom (e.g., nitrogen, phosphorus, sulfur)-doped carbon materials can influence the adsorption state of oxygen molecules and intermediates by changing the charge distribution of adjacent carbon atoms because of the difference in electronegativity and atomic radius between the heteroatoms and carbon atoms, thus promoting the ORR activity. Optimization of the structure and surface properties of carbon-based electrocatalysts has helped accelerate the four-electron reaction and reduce the overpotential in the ORR. Therefore, non-noble metal and heteroatom-doped carbon-based catalysts exhibit improved ORR activity. The dispersion of non-noble metals on carbon materials via the interaction of metal atoms with the neighboring nitrogen atoms or other heteroatoms produces high-density active sites in the carbon support, thus leading to high atomic utilization and significantly improving the electrocatalytic activity owing to the synergistic effect. This review focuses on the applications of carbon-based electrocatalysts in fuel cells, summarizing the design strategies and electrocatalytic activities of heteroatom-doped carbon-based catalysts with non-noble metals toward improving their ORR activity. Furthermore, the latest research progress in the field of carbon-based catalysts used as cathode catalysts in proton exchange membrane fuel cells (PEMFCs) and anion-exchange membrane fuel cells (AEMFCs) is integrated, and the direction of future development is addressed.

Cancer remains a major global cause of morbidity and mortality. Diagnosis at an early stage can significantly improve the survival of cancer patients. Cancers of different origins often have vastly different genotypes and phenotypes. Therefore, it is challenging to establish a universal strategy for cancer detection. Universal cancer detection can be potentially achieved by using pH-responsive probes. An acidic microenvironment is mainly caused by lactic acid accumulation in rapidly growing tumor cells. Based on the difference in pH between tumor and normal tissues, fluorescent materials that respond to a pH of around 6.8 are ideal for tumor detection. Carbon quantum dots (CQDs) have attracted much attention in bioimaging owing to their outstanding characteristics such as stable photoluminescence, low cytotoxicity, excellent biocompatibility, and resistance to photobleaching. In this study, red fluorescent CQDs (R-CQDs) were synthesized by the solvothermal treatment of 4-(dimethylamino) phenol in the presence of potassium periodate. The UV-Vis spectrum of the R-CQDs showed a characteristic absorption peak at 545 nm. The photoluminescence spectrum revealed an emission peak at 640 nm. The brightness of this photoluminescence peak was quantified to be 12.8% in terms of the absolute quantum yield (QY). Transmission electron microscopy (TEM) images showed that the R-CQDs have uniform sizes with an average diameter of 4 nm and a lattice spacing of 0.21 nm. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed that the R-CQDs have a large number of carboxyl groups. The Raman spectrum of the R-CQDs showed the characteristic D band at 1340 cm^-1 and G band at 1585 cm^-1. The X-ray powder diffraction (XRD) pattern showed a broad (002) peak centered at around 23°. The R-CQDs were responsive to highly acidic or alkaline conditions. The incorporation of a block copolymer (MeO-PEG-PDPA), prepared by atom transfer radical polymerization (ATRP), on the R-CQDs produced pH-responsive fluorescent CQDs (pRF-R-CQDs). Photoluminescence (PL) spectra showed that the pRF-R-CQDs were responsive at pH 6.8. At pH > 6.8, the fluorescence of the pRF-R-CQDs would be quenched because of deprotonation of the amine groups. In contrast, protonation of the amine groups would lead to a dramatic increase in fluorescence emission. TEM images showed that the pRF-R-CQDs self-assemble and disassemble at pH 6.8 because of their pH-responsive properties. Compared with most existing fluorescent materials, the pRF-R-CQDs can effectively resist photobleaching and autofluorescence. Moreover, these pRF-R-CQDs have minimal toxicity and can distinguish tumors from normal tissues. Therefore, pRF-R-CQDs have great potential for use as a universal material in tumor microenvironment diagnosis.

The hydrophobic ionic liquid (IL) 1-propyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C₃mim][NTf₂]) was synthesized according to traditional methods. By adding different amounts of diethyl carbonate (DEC) solvent and lithium bis[(trifluoromethyl)sulfonyl]imide ([Li][NTf₂]) salt to [C₃mim][NTf₂] IL, eight solution systems were prepared. First, the thermodynamic properties of the eight solution systems were characterized by differential scanning calorimetry (DSC). The semi-stable temperature of the system gradually disappeared with increasing lithium salt content, but the melting point temperature was not apparent in the experiment. These results indicate that DEC and lithium salts can dissolve in ILs within the tested temperature range. The basic properties of the eight systems, including thermodynamic and dynamic properties, were systematically studied at different temperatures. The variation in the self-diffusion coefficient of lithium ion ([Li]⁺) as a function of DEC concentration, density changes, viscosity, conductivity, and the viscosity/conductivity activation energy of the eight systems was calculated by the Vogel Fulcher Taman (VFT), Final Vogel Fulcher Taman (FVFT), and Arrhenius equations. The effect of temperature on the properties of the system was studied in detail. Within the temperature range measured herein, the deviation between the fitting equation and experimental value was small. Consequently, these equations were successfully used to calculate the properties of the system at various temperatures. All fitting parameters of the corresponding equations are provided herein. The viscosity for all systems decreased rapidly with increasing temperature, which increased the conductivity. Based on these experiments, the influence of DEC on the system microstructure was discussed in the context of the molecular dynamics simulation results. In particular, the interaction between [Li]⁺ and [NTf₂]^-/DEC was examined. In all solution systems, [NTf₂]^- coordinates to [Li]⁺ through only the O atom and not the N atom. Radial distribution function (RDF) analysis showed that the interaction between [Li]⁺ and [NTf₂]^- weakened with increasing DEC concentration. DEC molecules were observed in the first solvation layer of [Li]⁺ coordinating to [Li]⁺ through the carbonyl O atom. Although the interaction between [Li]⁺ and DEC was weakened, competition between [NTf₂]^- and DEC in the first solvation layer of [Li]⁺ was observed by the coordination number analysis of the O atom around [Li]⁺. Therefore, the introduction of DEC is beneficial for Li⁺ diffusion, which is consistent with the experimental results.

In 2005, the Science magazine, in commemorating the 125th anniversary of its founding, proposed 25 most challenging scientific issues in the future. One of the issues, "How far can we push chemical self-assembly?" has attracted the attention of scientists all over the world. During the 11th Five Year Plan period, NSFC convened scientists from various fields and proposed a major research project, "Controllable self-assembly system and its functionalization". Since the implementation of this project, Chinese scientists have developed and recognized a variety of noncovalent interactions, constructed numerous assembly building blocks with the "Chinese label", established a new assembly method similar to an organic "name reaction", realized the functions of multi-component and multi-level assemblies, and constructed a batch of controllable self-assembly systems having scientific importance and potential practical value. They have achieved great leap forward from following to original innovation, and brought the research of chemical self-assembly in China to move forward to the center of international stage. In this study, we examined the overall scientific goals, general layout of the plan, and ideas for implementation of the major research program "Controllable Self-Assembly System and its Functionalization", as well as an array of significant research accomplishments made possible through the funding received by the program.

The CO₂ level in the atmosphere has been increasing since the industrial revolution owing to anthropogenic activities. The increased CO₂ level has led to global warming and also has detrimental effects on human beings. Reducing the CO₂ level in the atmosphere is urgent for balancing the carbon cycle. In this regard, reduction in CO₂ emission and CO₂ storage and usage are the main strategies. Among these, CO₂ usage has been extensively explored, because it can reduce the CO₂ level and simultaneously provide opportunities for the development in catalysts and industries to convert CO₂ as a carbon source for preparing valuable products. However, transformation of CO₂ to other chemicals is challenging owing to its thermodynamic and kinetic stabilities. Among the CO₂ utilization techniques, electrochemical CO₂ reduction (ECR) is a promising alternative because it is generally conducted under ambient conditions, and water is used as the economical hydrogen source. Moreover, ECR offers a potential route to store electrical energy from renewable sources in the form of chemical energy, through generation of CO₂ reduction products. To improve the energy efficiency and viability of ECR, it is important to decrease the operational overpotential and maintain large current densities and high product selectivities; the development of efficient electrocatalysts is a critical aspect in this regard. To date, many kinds of materials have been designed and studied for application in ECR. Among these materials, metal oxide-based materials exhibit excellent performance as electrocatalysts for ECR and are attracting increasing attention in recent years. Investigation of the mechanism of reactions that involve metallic electrocatalysts has revealed the function of trace amount of oxidized metal species—it has been suggested that the presence of metal oxides and metal-oxygen bonds facilitates the activation of CO₂ and the subsequent formation and stabilization of the reaction intermediates, thereby resulting in high efficiency and selectivity of the ECR. Although the stability of metal oxides is a concern as they are prone to reduction under a cathodic potential, the catalytic performance of metal oxide-based catalysts can be maintained through careful designing of the morphology and structure of the materials. In addition, introducing other metal species to metal oxides and fabricating composites of metal oxides and other materials are effective strategies to achieve enhanced performance in ECR. In this review, we summarize the recent progress in the use of metal oxide-based materials as electrocatalysts and their application in ECR. The critical role, stability, and structure-performance relationship of the metal oxide-based materials for ECR are highlighted in the discussion. In the final part, we propose the future prospects for the development of metal oxide-based electrocatalysts for ECR.

Graphene fiber is a macroscopic carbonaceous fiber composed of microscopic graphene sheets, and has attracted extensive attention. Graphene building blocks form a highly ordered structure, resulting in fibers with the same properties as graphene, such as superior mechanical and electrical performance, low weight, excellent flexibility, and ease of functionalization. Moreover, graphene fibers are compatible with traditional textile technologies, facilitating the development of wearable electronics, flexible energy devices, and smart textiles. Graphene fibers were first prepared in 2011 by wet spinning of graphene oxide (GO) solution, which was dispersed in water. Various fabrication methods have been developed to assemble graphene sheets into fibers since then and different strategies have been proposed to optimize their structure and performance. Graphene fibers have applications in numerous fields, including conductors, sensors, actuators, smart textiles, and flexible energy devices. This review aims to provide a comprehensive picture of the preparation approaches, properties, and applications of graphene fibers. Firstly, the preparation processes, unique structures, and properties of three typical carbonaceous fibers-arbon fibers, carbon nanotube (CNT) fibers, and graphene fibers-re compared. It can be seen that graphene fibers possess the unique structures, such as the large grain sizes and highly aligned structure, endowing them with the outstanding properties. Then a variety of fabrication techniques have been summarized, including wet spinning, dry spinning, dry-jet wet spinning, space-confined hydrothermal assembly, film conversion approach, and template-assisted chemical vapor deposition (CVD). Wet spinning is a common method to fabricate high-performance graphene fibers and is promising for the large-scale production of graphene fibers. Besides, various strategies for improving the mechanical, electrical, and thermal properties of graphene fibers are introduced in detail, including well-chosen graphene building blocks, optimized fabrication processes, and high-temperature treatments. Although the electrical and thermal transport properties of typical graphene fibers are better than those of carbon fibers, the strength and modulus of graphene fibers are inferior. Therefore, the enhancement of the mechanical properties of graphene fibers by optimizing the composition of precursors, controlling and adjusting the assembly processes, and exploring feasible post-treatment procedures are essential. Meanwhile, the review outlines the applications of graphene fibers in high-performance conductors, functional fabrics, flexible sensors, actuators, fiber-shaped supercapacitors and batteries. Finally, the persisting challenges and the future scope of graphene fibers are discussed. We believe that graphene fibers will become a new structural and functional material that can be applied in numerous fields in the future, aided by the continuous development of materials and techniques.

Optogenetics is a neuromodulation technology that combines light control technology with genetic technology, thus allowing the selective activation and inhibition of the electrical activity in specific types of neurons with millisecond time resolution. Over the past several years, optogenetics has become a powerful tool for understanding the organization and functions of neural circuits, and it holds great promise to treat neurological disorders. To date, the excitation wavelengths of commonly employed opsins in optogenetics are located in the visible spectrum. This poses a serious limitation for neural activity regulation because the intense absorption and scattering of visible light by tissues lead to the loss of excitation light energy and also cause tissue heating. To regulate the activity of neurons in deep brain regions, it is necessary to implant optical fibers or optoelectronic devices into target brain areas, which however can induce severe tissue damage. Non- or minimally-invasive remote control technologies that can manipulate neural activity have been highly desirable in neuroscience research. Upconversion nanoparticles (UCNPs) can emit light with a short wavelength and high frequency upon excitation by light with a long wavelength and low frequency. Therefore, UCNPs can convert low-frequency near-infrared (NIR) light into high-frequency visible light for the activation of light-sensitive proteins, thus indirectly realizing the NIR optogenetic system. Because NIR light has a large tissue penetration depth, UCNP-mediated optogenetics has attracted significant interest for deep-tissue neuromodulation. However, in UCNP-mediated in vivo optogenetic experiments, as the up-conversion efficiency of UCNPs is low, it is generally necessary to apply high-power NIR light to obtain up-converted fluorescence with energy high enough to activate a photosensitive protein. High-power NIR light can cause thermal damage to tissues, which seriously restricts the applications of UCNPs in optogenetic technology. Therefore, the exploration of strategies to increase the up-conversion efficiency, fluorescence intensity, and biocompatibility of UCNPs is of great significance to their wide applications in optogenetic systems. This review summarizes recent developments and challenges in UCNP-mediated optogenetics for deep-brain neuromodulation. We firstly discuss the correspondence between the parameters of UCNPs and employed opsins in optogenetic experiments, which mainly include excitation wavelengths, emission wavelengths, and luminescent lifetimes. Thereafter, we introduce the methods to enhance the conversion efficiency of UCNPs, including optimizing the structure of UCNPs and modifying the organic dyes in UCNPs. In addition, we also discuss the future opportunities in combining UCNP-mediated optogenetics with flexible microelectrode technology for the long-term detection and regulation of neural activity in the case of minimal injury.

Graphene has become a research focus in recent years owing to its excellent characteristics, and glass is a commonly used material with high transparency and low cost. Graphene glass combines the excellent properties of both graphene and glass; graphene glass has not only high thermal conductivity, high electrical conductivity, and good surface hydrophobicity but also exhibits superior electrothermal conversion and wide-spectrum high-light-transmittance characteristics. Therefore, the study of graphene glass films is of theoretical value and practical significance. In this study, a high-purity glass-based (JGS1 quartz glass) multilayer graphene film was developed based on an atmospheric-pressure chemical vapor deposition (APCVD) method, and its electrical characteristics, light transmittance, and electrical heating characteristics were experimentally investigated in detail. The results show that graphene glass with different surface resistance values obtained through direct growth on a high-purity quartz glass substrate using the APCVD method, not only has excellent uniformity and quality, but also has considerably flat and high transmittance across the entire visible light region and exhibits excellent heating performance and fast response time. For graphene glass with a surface resistance of 1500 Ω·sq^-1, the light transmittance can reach 74%, and the saturation temperature can rise to 185 ℃ by applying a bias voltage of 40 V. In addition, when the resistance value of the graphene glass is 420 Ω·sq^-1, the graphene glass reaches a high saturation temperature of 325 ℃ in 40 s, and the corresponding heating rate can exceed 18 ℃·s^-1, achieving a significantly higher heating rate than other heating films at the same voltage. Compared with the polyethylene-terephthalate- (PET-) based and silicon-based graphene films obtained by the transfer, graphene glass has a higher saturation temperature, shorter thermal response time, and faster heating rate. Furthermore, graphene glass exhibits better heating cycle stability and longer-term heating stability at a constant voltage. In addition, an experiment using the graphene glass to thermally tune the wavelength of a vertical-cavity surface-emitting laser was conducted and gave good results. The position of the laser peak controlled by the graphene glass was red-shifted by 1.78 nm by applying a voltage of 20 V, and the wavelength tuning efficiency reached 0.059 nm·℃^-1. Compared with PET-based and silicon-based graphene films, the actual electrical heating capacity of graphene glass increased by 195%. These experimental findings demonstrate that graphene glass transparent films with excellent electric heating characteristics can be used in various transparent electric heating fields and have relatively wide application prospects.

Neural electrodes have been extensively utilized for the investigation of neural functions and the understanding of neuronal circuits because of their high spatial and temporal resolution. However, long-term effective electrophysiological recordings in free-behaving animals still constitute a challenging task, which hinders longitudinal studies on complex brain-processing mechanisms at a functional level. Herein, we demonstrate the feasibility and advantages of using a self-spreadable octopus-like electrode (octrode) array for long-term recordings. The octrode array was fabricated by enwrapping a bundle of eight formvar-coated nickel-chromium microwires with a layer of polyethylene glycol in a custom-made mold. After the electrodeposition of platinum nanoparticles, the microwires at the electrode tip were gathered together and then re-enwrapped with a thin layer of gelatin to maintain their structure and mechanical strength for implantation. Shortly after implantation (within 20 min), the biocompatible gelatin encapsulation swelled and dissolved, causing the self-spreading of the recording channels of the octrode array in the brain. The electrochemical characteristics of the electrode/neural tissue interface were investigated by electrochemical impedance spectroscopy (EIS). Four weeks after implantation, the average impedance of the octrodes (1.26 MΩ at 1 kHz) was significantly lower than that of the conventional tetrodes (1.50 MΩ at 1 kHz, p < 0.05, t-test). Additionally, the octrodes exhibited a better pseudo-capacitive characteristic and a considerably faster ion transfer rate at the electrode interface than the tetrodes. Spontaneous action potentials and local field potentials (LFPs) were also recorded in vivo to investigate the electrophysiological performance of the octrodes. The peak-to-peak spike amplitudes recorded for the octrodes were remarkably larger than those recorded for the tetrodes. The signal quality remained at approximately the same level for the four-week period, while the peak-to-peak spike amplitudes recorded for the tetrodes decreased abruptly. Moreover, the voltage amplitudes recorded by the octrodes at 1–200 Hz were notably larger than those by the tetrodes, suggesting a higher sensitivity in the recording of electrophysiological events. Furthermore, we performed immunochemical analyses on the brain tissues at post-implantation to evaluate the histocompatibility of the electrodes. Tissue responses of the octrodes were alleviated considerably, evidenced by the reduced astroglial intensity and increased neuron density around the implant site as compared to the tetrodes, which may be due to the relatively small size of each decentralized recording channel after self-spreading in vivo. Generally, the fabricated octrodes exhibited a lower electrochemical impedance value at the octrode/neural tissue interface and an increased signal quality during the long-term electrophysiological recording in freely moving mice as compared to the conventional tetrodes. All of these are desirable characteristics in neural circuit dissections in vivo.

Newly established in 2018, the UK Research and Innovation (UKRI) strengthens the strategic coordination of the UK research and innovation system by bringing together seven Research Councils, Research England, and Innovate UK. Through its nine organizations, UKRI funds multidisciplinary and interdisciplinary research in a number of priority areas. It also runs the Strategic Priorities Fund to support multidisciplinary and interdisciplinary research in strategic areas identified by government policies as well as the Global Challenges Research Fund to promote challenge-led interdisciplinary research needed by developing countries. The UKRI makes significant efforts to engage stakeholders in the development, design, and implementation of multidisciplinary and interdisciplinary programs. It has also developed a range of mechanisms to improve the evaluation of multidisciplinary and interdisciplinary projects. Chinese science and innovation funding agencies could draw upon the UKRI experience from four aspects to advance interdisciplinary research in China.

The pair of molecular acidity and basicity is one of the most widely used chemical concepts in chemistry, biology, and other related fields. Nevertheless, quantitative determination of these intrinsic physical properties from the perspective of theory and computation is still an unresolved task at present. Earlier, we proposed to utilize the molecular electrostatic potential and natural atomic orbital from conceptual density functional theory for this purpose. Later, we also proposed utilizing quantities from the information-theoretic approach in the density functional reactivity theory such as Shannon entropy, Fisher information, and information gain to quantify electrophilicity, nucleophilicity, regioselectivity, and stereoselectivity. The latter was successfully applied later to five series of molecular systems for determining the molecular acidity, including singly and doubly substituted benzoic acids, benzenesulfonic acids, benzeneseleninic acids, phenols, and alkyl carboxylic acids, whose validity and effectiveness have been sufficiently corroborated. As a continuation of our recent efforts along this line, in this work, we generalize our previous approaches by combining these two approaches together as a new set of descriptors to quantify the molecular basicity. The applicability and usefulness of our new approach are demonstrated hereby by three types of amines, namely, primary, secondary, and tertiary amines, with a total of 179 systems. We show that this new set of descriptors, including the molecular electrostatic potential or its equivalence, the natural valence atomic orbital energy, and quantities from information-theoretic approach such as Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy, information gain, Onicescu information energy, and relative Rényi entropy, is able to accurately predict the experimental pK_a values for the three types of amines. Our findings confirm that each of these quantities possesses strong linear correlation with the experimental pK_a value, though less significantly than expected. Moreover, when combined, these quantities can yield accurate and quantitative models for determining the molecular basicity of all the three types of amines. The reason behind this is that all these descriptors are simple electron density functionals. According to the basic theorem of density functional theory, they should contain adequate information for the determination of all the physio-chemical properties in the ground state of molecular systems, including molecular acidity and basicity. Our present results predict that this new approach should be readily applicable to many other molecular species, thereby providing an effective and robust approach to appreciate chemical concepts such as acidity and basicity.

The development of highly efficient and low-cost electrocatalysts is important for both hydrogen- and carbon-based energy technologies. The electronic structure and coordination features, particularly the coordination environment and the amount of low-coordination atoms, of the catalyst are key factors that determine their catalytic activity and stability in a particular reaction. The regulation and rational design of catalytic materials at the molecular and atomic levels are crucial to achieving precise chemical synthesis at the atomic scale. Recently, significant efforts have been made to engineer coordination features and electronic structures by reducing the particle size, tuning the composition of the edges, and exposing specific planes of crystals. Among these representative strategies, the methods based on the confinement effect are most effective for achieving precise chemical synthesis with atomic precision at the molecular and atomic levels. Under molecular or atomic scale confinement, the physicochemical properties are largely altered, and the chemical reactions as well as the catalytic process are completely changed. The unique spatial and dimensional properties of the confinement regulate the molecular structure, atomic arrangement, electron transfer, and other properties of matter in space. It not only adjusts the coordination environments to control the formation mechanism of active centers, but also influences the structural and electronic properties of electrocatalysts. Therefore, the adsorption of catalytic intermediates is altered, and consequently, the catalytic activity and selectivity are changed. In a confined reaction, usually in suitable nano-reactors, the physicochemical properties of reaction products, such as the state of matter, solubility, dielectric constant, and molecular orbital, are finely modulated. Thus, the catalysts produced by confinement significantly differ from those produced in an open system. For example, atomic-layered metals with low coordination can be produced in a two-dimensional confined space. The nitrogen configurations of nitrogen-doped graphene can also be regulated in two-dimensional or three-dimensional confined systems. Herein, the confinement-induced methods, specifically the method used for atomic regulation, are reviewed, such as the control of molecular configuration, the modification of the coordination structure, and the alteration of charge transfer. Applications in the field of fuel cells and material energy conversion are also reviewed. In the next stage, it is important to conduct in-depth investigations of the constructed confinement environment by selecting different substrates for the regulation and rational design of confined catalytic materials. The investigation of the derived properties of the catalyst after release from the confinement is crucial for the development of uncommon catalytic properties.

Bacterial infection is a major threat to human health, and can cause several diseases including gastroenteritis, influenza, tetanus, and tuberculosis. As conventional antibiotic treatment may cause various undesirable effects such as stomach disorder and bacterial resistance, it is necessary to improve the antibacterial efficiency of antibiotics. Here, we synthesized a peptide-based copolymer, poly(ε-caprolactone)-block-poly(glutamic acid)-block-poly(lysine-stat-phenylalanine)[PCL₃₄-b-PGA₃₀-b-P(Lys₁₆-stat-Phe₁₂)] by ring-opening polymerization (ROP) of ε-caprolactone and amino acid N-carboxyanhydride (NCA). Successful synthesis of the copolymer was verified by proton nuclear magnetic resonance and size exclusion chromatography. This copolymer can self-assemble into negatively charged micelles (-26.7 mV) under alkaline conditions by solvent switch method. The micelle structure was confirmed by transmission electron microscopy and dynamic light scattering, and revealed to have a diameter of ~42 nm. Antibiotics were loaded into micelles during the self-assembly process, and cell viability assay was conducted to evaluate its cytotoxicity with and without tobramycin. No obvious cytotoxicity was observed for both micelles when the concentration was lower than 300 μg·mL^-1. The antibiotic-loaded micelles demonstrated very low minimum inhibitory concentrations (MICs) against both Gram-negative Escherichia coli (E. coli) (7.8 μg·mL^-1) and Gram-positive Staphylococcus aureus (S. aureus) (18.2 μg·mL^-1), while the MICs of free tobramycin were 3.9 and 1.0 μg·mL^-1, respectively. The drug-loading content and efficiency of the micelles were 5.2% and 24.3%, respectively. Therefore, the MICs of the loaded tobramycin against E. coli and S. aureus were 0.4 and 0.9 μg·mL^-1, respectively, suggesting that the micelle could enhance the antibacterial activity of antibiotics. Tobramycin-loaded micelles demonstrated a sustained release characteristic, with 85% of the antibiotics released after 8 h. In bacteria-induced acidic microenvironment, the coil conformation of PGA blocks transforms and PGA blocks shrink toward the micelle core. Concomitantly, the carboxyl side chains are protonated in an acidic environment, increasing the hydrophobicity of this micelle. Antibiotics will be captured when reaching the outer core to slow down the releasing process. Furthermore, the poly(lysine-stat-phenylalanine) [P(Lys-stat-Phe)] coronas with broad spectrum intrinsic antibacterial activity can penetrate the bacterial cell membrane, leading to leakage of the cellular contents of the bacteria and ultimately their death. Due to the sustained release property of micelle and the intrinsic activity of the antibacterial peptide segments, this micelle can greatly enhance the antibacterial activity of antibiotics. Overall, this antibiotic-loaded micelle provides a novel approach for significantly reducing the antibiotics dosage and avoiding the associated health risks.

Organic photocatalysts have attracted attention owing to their suitable redox band positions, low cost, high chemical stability, and good tunability of their framework and electronic structure. As a novel organic photocatalyst, PDI-Ala (N, N'-bis(propionic acid)-perylene-3, 4, 9, 10-tetracarboxylic diimide) has strong visible-light response, low valence band position, and strong oxidation ability. However, the low photogenerated charge transfer rate and high carrier recombination rate limit its application. Due to the aromatic heterocyclic structure of g-C₃N₄ and large delocalized π bond in the planar structure of PDI-Ala, g-C₃N₄ and PDI-Ala can be tightly combined through π–π interactions and N―C bond. The band structure of sulfur-doped g-C₃N₄ (S-C₃N₄) matched well with PDI-Ala than that with g-C₃N₄. The electron delocalization effect, internal electric field, and newly formed chemical bond jointly promote the separation and migration of photogenerated carriers between PDI-Ala and S-C₃N₄. To this end, a novel step-scheme (S-scheme) heterojunction photocatalyst comprising organic semiconductor PDI-Ala and S-C₃N₄ was prepared by an in situ self-assembly strategy. Meanwhile, PDI-Ala was self-assembled by transverse hydrogen bonding and longitudinal π–π stacking. The crystal structure, morphology, valency, optical properties, stability, and energy band structure of the PDI-Ala/S-C₃N₄ photocatalysts were systematically analyzed and studied by various characterization methods such as X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, ultraviolet visible diffuse reflectance spectroscopy, electrochemical impedance spectroscopy, and Mott-Schottky curve. The work functions and interface coupling characteristics were determined using density functional theory. The photocatalytic activities of the synthesized photocatalyst for H₂O₂ production and the degradation of tetracycline (TC) and p-nitrophenol (PNP) under visible-light irradiation are discussed. The PDI-Ala/S-C₃N₄ S-scheme heterojunction with band matching and tight interface bonding accelerates the intermolecular electron transfer and broadens the visible-light response range of the heterojunction. In addition, in the processes of the PDI-Ala/S-C₃N₄ photocatalytic degradation reaction, a variety of active species (h⁺, ·O₂^-, and H₂O₂) were produced and accumulated. Therefore, the PDI-Ala/S-C₃N₄ heterojunction exhibited enhanced photocatalytic performance in the degradation of TC, PNP, and H₂O₂ production. Under visible-light irradiation, the optimum 30%PDI-Ala/S-C₃N₄ removed 90% of TC within 90 min. In addition, 30%PDI-Ala/S-C₃N₄ displayed the highest H₂O₂ evolution rate of 28.3 μmol·h^-1·g^-1, which was 2.9 and 1.6 times higher than those of PDI-Ala and S-C₃N₄, respectively. These results reveal that the all organic photocatalyst comprising PDI-based supramolecular and S-C₃N₄ can be efficiently applied for the degradation of organic pollutants and production of H₂O₂. This work not only provides a novel strategy for the design of all organic S-scheme heterojunctions but also provides a new insight and reference for understanding the structure–activity relationship of heterostructure catalysts with effective interface bonding.

Sleep deprivation (SD) is the partial or complete loss of sleep and has long been used as a tool in sleep research to interfere with normal sleep cycles in rodents and humans. The progressively-accumulating sleep pressure induced by sleep deprivation can lead to a variety of physiological changes and even death. Compared to traditional detection methods, in vivo detection of neuronal activity using micro-electromechanical system (MEMS) technology following sleep deprivation can help fully elucidate the effects of sleep deprivation at the cellular level. Herein, a computer-controlled rotary roller was used to completely deprive rats of sleep for 14 days and 16-channel microelectrode arrays (MEAs) were fabricated and implanted into the rat hippocampus to measure neural spikes and local field potentials (LFPs) in real-time. The hippocampus is involved in learning and memory and has been the focus of intensive research aimed at understanding the function of sleep. This study was performed to measure the changes in neuronal activity in the rat hippocampus induced by sleep deprivation as well as their overall impact on the brain. After sleep deprivation, both the pyramidal- and inter-neurons showed a higher amplitude and more intense firing patterns. The fast-firing pattern of the neurons after sleep deprivation indicated elevated excitability in the prolonged awake state. In addition, the LFP of the sleep deprived rats fluctuated more frequently. The power of the LFPs in the low-frequency band (0–50 Hz) was calculated, showing increased power of the delta, theta, alpha, and beta bands after sleep deprivation, especially for the delta band (0.1–4 Hz). Generally, LFPs are generated by all types of neural activity in the neural circuit, and the changes in the low frequency band power suggested decreased arousal and increased sleep pressure induced by sleep deprivation, which could further impair brain function. This study was mainly aimed at measuring electrophysiological changes induced by sleep deprivation in the rat brain. Typically, neuronal activity changes were accompanied by the alternation of specific neurotransmitters in the brain. In the future, it will be essential to focus on measuring the concurrent change of electrophysiological and neurochemical signals to better examine the impact of sleep deprivation on brain function.

Carbon dioxide (CO₂) is one of the main greenhouse gases in the atmosphere. The conversion of CO₂ into solar fuels (CO, HCOOH, CH₄, CH₃OH, etc.) using artificial photosynthetic systems is an ideal way to utilize CO₂ as a resource and reduce CO₂ emissions. A typical artificial photosynthetic system is composed of three key components: a photosensitizer (PS) to harvest visible light, a catalyst (C) to catalyze CO₂ or protons into carbon-based fuels or H₂, respectively, and a sacrificial electron donor (SED) to consume the holes generated in the PS. In most cases, the PS and catalyst are two different components of a system. However, some components that possess both light harvesting and redox catalysis functionalities, e.g., nano-semiconductors, are referred to as photocatalysts. During photocatalysis, the PS is typically excited by photons to generate excited electrons. The excited electrons in the PS are transferred to the catalyst to generate a reduced catalyst. The reduced catalyst is used as an active intermediate to perform CO₂ binding and transformation. The PS can be recovered through a reaction with the SED. Nano-semiconductors have been used as photosensitizers and/or photocatalysts in photocatalytic CO₂ reduction systems owing to their excellent photophysical and photochemical properties and photostability. CdS and CdSe nano-semiconductors, such as quantum dots, nanorods, and nanosheets, have been widely used in the construction of photocatalytic CO₂ reduction systems. Systems based on CdS or CdSe nano-semiconductors can be classified into three categories. The first category is systems based on CdS or CdSe photocatalysts. In these systems, CdS or CdSe nano-semiconductors function as photocatalysts to catalyze CO₂ reduction without a co-catalyst under visible-light irradiation. The CO₂ reduction reaction occurs at the surface of the CdS or CdSe nano-semiconductors. The second category is systems based on CdS or CdSe composite photocatalysts. CdS or CdSe nano-semiconductors are combined with functional materials, such as reduced graphene oxide or TiO₂, to prepare composite photocatalysts. These composite photocatalysts are expected to improve the lifetime of the charge separation state and inhibit the photocorrosion of the nano-semiconductors during photocatalysis. The third category is hybrid systems containing a CdS nano-semiconductor and molecular catalysts, such as nickel and cobalt complexes and iron porphyrin. In these hybrid systems, CdS functions as a photosensitizer and the CO₂ reduction reaction occurs at the molecular catalyst. This review article introduces the construction of artificial photosynthetic systems and the photocatalytic mechanism of nano-semiconductors, and summarizes the representative works in the three aforementioned categories of systems. Finally, the challenges of nano-semiconductors for photocatalytic CO₂ reduction are discussed.

In recent years, electrochemical water splitting that involves the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has attracted widespread attention because the process is clean, environmentally friendly, and the generated oxygen/hydrogen gas can be converted into electricity in a fuel cell. However, the HER and OER kinetics are sluggish and require highly efficient electrocatalysts for enhancing the reaction rate. Currently, precious metals such as Pt and RuO₂ have shown excellent HER and OER performance, respectively, but their practical applications are limited by their scarcity and high price. Therefore, the use of 3d transition metals, such as iron (Fe) and nickel (Ni), as electrocatalysts has attracted significant attention. To obtain a catalytic performance similar to that of precious metals, several methods have been explored, such as alloying 3d transition metals with precious metals, compositing a variety of transition metals, or requiring good carbon-based materials as a supporter. Metal-organic framework (MOF)-derived nanomaterials have emerged as some of the most promising non-precious metal bifunctional electrocatalysts. The MOF structure consists of metal-based units and special organic ligands, and after annealing, metal atoms can be converted into unsaturated metal-based active sites, and the organic ligands can be converted into carbon support. This could accelerate the charge transfer efficiency and can be beneficial for achieving excellent HER and OER performance. However, bifunctional electrocatalysts derived from nickel (Ni)-based MOFs have not been studied intensively, and their catalytic activity and stability remain to be improved. Herein, a Ni-MOF precursor was synthesized via a liquid-phase coordination reaction using Ni²⁺ and benzene-1, 3, 5-tricarboxylic acid. The obtained Ni-MOF samples were annealed under H₂/Ar atmosphere at 600, 700, and 800 ℃, named Ni/C-H₂-600, Ni/C-H₂-700, Ni/C-Ar-700, and Ni/C-H₂-800, respectively. During high-temperature annealing treatment, Ni nanoparticles were grown in situ on a rod-shaped carbon substrate to form novel hybrid architecture Ni/C nanoparticles used as a high-performance bifunctional electrocatalyst for overall water splitting. The HER overpotential of Ni/C-H₂-700 was 120 mV at a current density of 10 mA∙cm⁻², which is much lower than that of Ni/C-H₂-600 (250 mV), Ni/C-H₂-800 (348 mV), and Ni/C-Ar-700 (275 mV). Ni/C-H₂-700 required an OER overpotential of 350 mV to achieve a current density of 10 mA∙cm⁻², which is lower than that of Ni/C-H₂-600 (370 mV), Ni/C-H₂-800 (430 mV), and Ni/C-Ar-700 (380 mV). Furthermore, Ni/C-H₂-700 showed the idea of HER and OER durability. Presumably, good structural properties and the abundant surface area of the carbon substrate elevated HER/OER activity owing to the synergistic advantages of accessible active sites and enhanced electronic conductivity.

Ever-increasing energy demands due to rapid industrialization and urban population growth have drastically reduced petroleum reserves and increased greenhouse-gas production, and the latter has consequently contributed to climate change and environmental damage. Therefore, it is highly desirable to produce fuels and chemicals from non-petroleum feedstocks and to reduce the atmospheric concentrations of greenhouse gases. One solution has involved using carbon dioxide (CO₂), a main greenhouse gas, as a C1 feedstock for producing industrial fuels and chemicals. However, this requires high energy input from reductants or reactants with relatively high free energy (e.g., H₂ gas) because CO₂ is a highly oxidized, thermodynamically stable form of carbon. H₂ can be generated through water photolysis, making it an ideal reductant for hydrogenating CO₂ to CO. In situ generation of CO such as this has been developed for various carbonylation reactions that produce high value-added chemicals and avoid deriving CO from fossil fuels. This is beneficial because CO is toxic, and when extracted from fossil fuels it requires tedious separation and transportation. This combination of CO₂ and H₂ allows for functional molecules to be synthesized as entries into the chemical industry value chain and would generate a carbon footprint much lower than that of conventional petrochemical pathways. Based on this, CO₂/H₂ carbonylations using homogeneous transition metal-based catalysts have attracted increasing attention. Through this process, alkenes have been converted to alcohols, carboxylic acids, amines, and aldehydes. Heterogeneous catalysis has also provided an innovative approach for the carbonylation of alkenes with CO₂/H₂. Based on these alkene carbonylations, the scope of CO₂/H₂ carbonylations has been expanded to include aryl halides, methanol, and methanol derivatives, which give the corresponding aryl aldehyde, acetic acid, and ethanol products. These carbonylations revealed indirect CO₂-HCOOH-CO pathways and direct CO₂ insertion pathways. The use of this process is ever-increasing and has expanded the scope of CO₂ utilization to produce novel, high value-added or bulk chemicals, and has promoted sustainable chemistry. This review summarizes the recent advances in transition-metal-catalyzed carbonylations with CO₂/H₂ and discusses the perspectives and challenges of further research.

Proton-exchange membrane fuel cells (PEMFCs) directly transform chemical energy into electrical energy with high energy density and zero carbon emissions, thereby offering a clean energy alternative for fossil fuels and vehicle electrification. However, the existing PEMFCs rely on Pt-based catalysts, especially at the cathode side wherein the sluggish oxygen reduction reaction (ORR) takes place, resulting in high cost and limiting their commercial applications. Therefore, there is a strong interest in developing platinum group metal-free (PGM-free) PEMFCs. Although impressive advancements have been made since metal-nitrogen-carbon (M-N-C) catalysts have been developed as promising candidates for low-cost cathode catalysts, PGM-free PEMFCs still suffer from insufficient activity and durability. Owing to the intricate structure of the tri-phase interface and mass transport limitation, the M-N-C catalysts with high ORR activity in rotating disk electrode (RDE) tests still suffer from unexpected problems such as showing low activity and undesired rapid degradation process in real fuel cell conditions. Therefore, a comprehensive understanding of the active sites and influences of the M-N-C catalyst structure and cathode structure on the PEMFC performance will promote the development of PGM-free PEMFCs. Herein, with an aim to increase the activity and durability of PEMFCs based on M-N-C catalysts, we summarize the recent progress in understanding the active sites of M-N-C catalysts and the relationships between the structures of catalysts/catalyst layers and device performances. At the catalyst level, multiple delicately designed synthetic strategies suggest that attractive device performances can be obtained by tailoring the intrinsic activity and density of the catalyst active sites while engineering the porosity of catalysts to improve the utilization of active sites. Additionally, integrating the catalyst ink into the cathode catalyst layers in PGM-free PEMFC is pivotal for transforming the impressive ORR performance of catalysts in the RDE test to fuel cell performance. Accordingly, the recent advances in the enhancement of mass transfer and charge transport to achieve remarkable fuel cell performance were also included by rationally designing ionomer contents, catalyst morphology, and fabrication process of cathodic catalyst layers. Moreover, durability is the Achilles heel of PEMFCs with M-N-C catalysts, which is currently far behind the commercial requirements. The possible degradation mechanisms and the recent progress in seeking the corresponding solutions are also discussed in this review, including the decomposition of metal species, protonation of nitrogen sites, corrosion of carbon support, and micropore flooding. Based on these insights, the perspective is proposed by articulating open challenges and opportunities in materials innovations and device engineering with an aim to achieve practical M-N-C based PEMFCs.

Proton exchange membrane fuel cells (PEMFCs) are considered as one of the most promising energy conversion devices owing to their high power density, high energy conversion efficiency, environment-friendly merit, and low operating temperature. In the cathodic oxygen reduction reaction and anodic small-molecule oxidation reactions, Pt shows excellent catalytic activity. However, several factors limit the practical application of Pt nanoparticles in fuel cells, such as the high price of Pt, easy agglomeration during long-term cycling, and limited electrocatalytic performance. Alloying Pt with 3d-transition metal produces ligand and strain effects, which reduces the center of Pt-d band and weakens the binding strength of oxygen species, thereby improving the catalytic activity and reducing the cost. However, the performance of fuel cells degrades seriously because the transition metals tend to dissolve in acidic electrolytes. The disordered alloy transformed into ordered intermetallic nanoparticles can prevent the dissolution of transition metals. Ordered intermetallics have highly ordered atomic arrangements and strong Pt(5d)-M(3d) orbital interactions, which result in excellent stability in both acidic and alkaline electrolytes. Ordered intermetallic nanoparticles have attracted significant attention owing to their excellent electrocatalytic activity and stability, which can be attributed to controllable composition and structure. Pd has a similar electronic structure and lattice parameters to Pt, and has thus attracted significant attention. Several Pd-based ordered intermetallics have been synthesized, and they exhibit sufficient catalytic performance. This review discusses the recent progress in noble metal-based ordered intermetallic electrocatalysts based on the research status of our group over the years. First, the structural characteristics and characterization methods of ordered intermetallic nanoparticles are introduced, exhibiting approaches to distinguish ordered and disordered phases. Then, the controllable preparation of ordered nanoparticles is highlighted, including thermal annealing and direct liquid phase synthesis. The migration and interdiffusion of atoms in the ordering process is very difficult. High-temperature thermal annealing is the most commonly used method for preparing intermetallics, which can precisely control the composition and atomic ordered arrangement. However, thermal annealing can only produce thermodynamically stable spherical nanoparticles. Supports and coating layers are usually employed to prevent agglomeration of nanoparticles at high temperatures. Finally, the applications of ordered intermetallic nanoparticles in fuel cell electrocatalysts are reviewed, including the oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), formic acid oxidation reaction (FAOR), methanol oxidation reaction (MOR), and ethanol oxidation reaction (EOR). In addition, the current challenges and future development directions of the catalysts are discussed and discussed to provide new ideas for the development of fuel cell electrocatalysts.

Silicon-based neural probes are practical tools for recording neural cell firing. A single silicon-based needle with a width of only 70 μm, prepared using the standard complementary metal-oxide-semiconductor (CMOS) process technology, can contain thousands of electrode-recording sites. Optogenetics has made control over neuronal activity more precise. By recording the electrical activity of neurons stimulated by light, more information about brain activity can be recorded and analyzed. When yellow light or blue light is used to stimulate neurons, the photon energy is greater than the forbidden bandwidth of the silicon substrate, and the valence-band electrons are excited to the conduction band, generating electron-hole pairs. The photoinduced carrier in the silicon substrate severely disrupts the probe's signal-to-noise ratio. Decreasing the disturbance caused by light is a pragmatic way to execute recording and stimulating simultaneously. The traditional noise reduction method involves using heavily doped silicon as the substrate, reducing the carrier life by increasing the impurity concentration, and then reducing the noise of the silicon electrode under illumination. However, the heavily doped silicon substrate has more lattice defects than its lightly doped counterparts, which makes the silicon electrode fragile, and this method is not compatible with the standard CMOS process technology. On analyzing the photoinduced noise mechanism of manufacturing electrodes on lightly doped silicon substrates, we found that the inhomogeneous distribution of carriers generated by light excitation polarizes lightly doped silicon substrates. The potential caused by photoinduced polarization will affect the electrodes fabricated on it. Metalizing and grounding the lightly doped silicon substrate will effectively decrease the polarization potential. On using this method, the noise amplitude caused by the illumination can drop to 0.87% of the original value. To ensure an appropriate firing rate of neurons, the photo-stimulation frequency was chosen to be 20 Hz. Under the illumination of 1 mW·mm^-2, the background noise of the electrode could be controlled below 45 μV, which meets the needs for general optogenetics applications. Modification of the lightly doped silicon substrate will meet the requirements of the neural electrode for optogenetics applications. Unlike the traditional method of reducing light-induced noise by heavily doping the entire substrate, the noise reduction method of lightly doped silicon substrate is compatible with the standard CMOS process technology. It provides a noise cancellation method for the preparation of silicon-based neural microelectrodes with dense recording sites and high channel count using standard CMOS processes.

In recent years, lead-halide perovskites, one of the most competitive material types in the field of semiconductors, has attracted widespread attention because of its easy preparation, low cost, and high performance. Lead-halide perovskites are a type of material with an ABX₃ structure, in which A is an organic or inorganic monovalent cation, B is a divalent cation, and X is a halogen ion. Among them, the B-site ion and X-site ion form an octahedron, with the B-site ion occupying the center and the X-site ion located at the apex of the octahedron. This type of octahedron can undergo lattice changes such as rotation or tilt through the replacement of different halogen anions, which affects the material band gap. The octahedron is located in the center of a cube, which is composed of A-site ions. These structures constitute the basic unit of the perovskite. Compared with the widely used Ⅱ-Ⅵ or Ⅲ-Ⅴ semiconductor nanocrystalline materials, perovskite nanocrystals have great application potential owing to their superior optoelectronic performance. However, their stability problem restricts further development, making them unable to compete in commercial applications. Studies on the stability of perovskite materials began in 2009. It was discovered through experiments that perovskite materials would undergo irreversible degradation under the action of liquid polar solvents, which confirmed that humidity and air are important factors in perovskite degradation. With further research, the problem of illumination has also come to the surface. It was found through experiment that, when oxygen and humidity were excluded, the light condition could also have a certain negative impact on perovskite materials, and subsequently perform a certain repair effect. Research in this area can lay a foundation for the preparation of high-stability perovskite materials and devices, adjust the structure and performance of perovskite by lighting technology (especially laser irradiation), and expand its comprehensive application in the field of optoelectronics. This article focuses on the changes in perovskites under laser irradiation and the related applications. First, it reviews the unstable changes and micro-mechanisms that laser-irradiation induces in lead-halide perovskites, including accelerated degradation, repair of defects, segregation, phase transitions, and changes in the grain size. Second, based on these mechanisms, it explains how researchers have recently used laser-irradiation technology to control the performance of perovskite films and devices. In addition, it also introduces the application of the laser direct writing process in the fields of perovskite patterning and photoelectric detection. Finally, this paper summarizes the changes induced by the laser-irradiation illumination and applications of laser-irradiated lead-halide perovskites.

With the development of electric vehicles (EVs) and hybrid electric vehicles (HEVs), the demand for lithium ion power batteries with high energy density and long cycle life has continuously increased in the recent years. According to the "Made in China 2025" plan, the energy densities of lithium ion batteries need to reach 300 Wh·kg^-1 in 2020. Due to their high discharge capacities and work voltages, Ni-rich layered materials have attracted considerable attention from the science and industry fields as one of the most promising cathodes to achieve high energy density. According to previous reports, the discharge capacities of Ni-rich cathodes were positively correlated to their Ni content. However, the increased Ni content can aggravate the side reactions between the cathode and electrolyte, induce O loss, and trigger structural transformation from the surface to bulk. In this study, ZrO₂ was coated on LiNi_0.8Co_0.1Mn_0.1O₂ with a simple wet chemical method to improve its cycle performance. The scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) demonstrated that Zr was only detected in the ZrO₂-coated samples and was mainly distributed at the surface of the secondary particles of the LiNi_0.8Co_0.1Mn_0.1O₂ cathodes. The X-ray diffraction (XRD) indicated that Zr⁴⁺ in ZrO₂ migrated into the layered surface structure of LiNi_0.8Co_0.1Mn_0.1O₂ based on the shift of the (003) peak to a lower angle, which was considered as a lattice expansion along the c axis. Under the cut-off voltage of 4.3 and 4.5 V, the capacity retentions of the LiNi_0.8Co_0.1Mn_0.1O₂ cathodes improved from 84.89 to 97.61% and 75.60 to 81.37%, respectively, after 100 cycles at 1C. This was mainly attributed to the doped Zr⁴⁺ in surface structure as opposed to the ZrO₂ coating. The X-ray photoelectron spectroscopy (XPS) indicated that the Ni³⁺ at the surface of LiNi_0.8Co_0.1Mn_0.1O₂ was reduced to Ni²⁺ after the Zr⁴⁺ surface doping due to charge balance. Rietveld refinement also indicated that the Li⁺/Ni²⁺ cation disordering improved after the Zr⁴⁺ in ZrO₂ doped into NCM surface structure. The raised cation disordering may be triggered by the increased content of Ni²⁺ and their migration into Li layers due to the similar ion radius of Li⁺ (0.076 nm) and Ni²⁺ (0.069 nm). A structure-reconstructed layer at the surface of LiNi_0.8Co_0.1Mn_0.1O₂ was formed after the Zr⁴⁺ doping, which had been confirmed by transmission electron microscope (TEM). It was determined that this structure-reconstructed layer can hinder the side reactions at the interface and stabilize the bulk structure during cycles; thus, the cycle stability of LiNi_0.8Co_0.1Mn_0.1O₂ material was improved.