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.

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.

The storage and utilization of energy is one of the important topics in the development of science and technology, especially regarding secondary batteries, which are efficient electrical-/chemical-energy-converting devices. This review systematically introduces the important research progress made in the context of secondary batteries, starting from their development and leading to the introduction of related basic theoretical knowledge. The current research on secondary batteries that are based on different systems and related key materials is discussed in detail, and includes lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, magnesium-ion batteries, zinc-ion batteries, calcium-ion batteries, aluminum-ion batteries, fluorine-ion batteries, chloride-ion batteries, dual-ion batteries, lithium-sulfur (Se) batteries, sodium-sulfur (Se) batteries, potassium-sulfur (Se) batteries, polyvalent metal-sulfur-based batteries, lithium-oxygen batteries, sodium-oxygen batteries, potassium-oxygen batteries, aqueous metal-ion batteries, polyvalent metal-oxygen batteries, lithium-bromine (or lithium-iodine) batteries, photo-assisted batteries, flexible batteries, organic batteries, and metal-carbon dioxide batteries. Additionally, the common characterization techniques for electrode reaction processes in battery research are also introduced, including cryo-electron microscopy, transmission electron microscopy, synchrotron radiation, in situ spectroscopic techniques, and magnetic characterization. This paper will help researchers to systematically understand secondary battery technology and provide good guidance for future research on secondary batteries.

Graphene fiber material is one type of macroscopically one-dimensional materials assembled by graphene building blocks or coating graphene on other fibrous building blocks. The typical graphene fiber materials can be classified into graphene fiber and graphene-coated hybrid fiber based on their different building blocks. This type of materials exhibits superior tensile strength, excellent electrical and thermal conductivities, making them favorable for applications in flexible energy storage devices, electromagnetic shielding and wearable electronics. Recently, the chemical vapor deposition (CVD) method, conventionally used for fabricating film-like graphene, has been widely applied to the synthesis of graphene fiber materials. For preparing graphene fiber, the use of CVD method can prevent the complicated and time-consuming reducing treatment of graphene oxide (GO), which is well known as an imperative step in the commonly used wet spinning method. For preparing graphene-coated hybrid fiber, the CVD method can achieve an efficient modulation of graphene quality, and ensure a strong adhesion between graphene and fibrous substrates. In this review, we summarized the CVD methods for fabricating graphene fiber materials, including graphene-assembled graphene fiber and graphene-coated hybrid fiber, and introduced their excellent mechanical, electrical, thermal and optical properties along with their broad applications in intelligent sensors, optoelectronic devices, and flexible electrodes. Furthermore, the challenges in synthesizing CVD-fabricated graphene fiber materials were also analyzed. This review can be briefly divided into three parts: (1) Synthesis of graphene fibers: Up to now, the CVD method is a feasible and effective way to synthesize graphene with high crystallinity. The CVD strategies for fabricating graphene fibers mainly consist of the template method, the secondary growth method, and the film-scrolling method, which can simplify the fabrication process and efficiently modulate graphene quality. (2) Synthesis of graphene glass fibers: Similar to graphene growth directly on non-catalytic glass surfaces, CVD method can also be applied to synthesize graphene on glass fibers. By modifying the experimental parameters (carbon source, pressure, temperature, etc.), high-quality graphene films with controllable thickness can be uniformly coated on glass fibers. Meanwhile, the as-fabricated graphene glass fiber can be further used as a high-performance flexible electrode, electro-optic modulator, or electrocatalyst. (3) Synthesis of graphene metal fibers: Graphene can be controllably grown on metal fibers using the CVD method. Compared to the bare metal fiber, the fabricated graphene metal fiber exhibited enhanced electrical and thermal conductivities as well as better chemical stability, which can expand its applications in ultra-thin electronics and high-power circuits.

Owing to the rapid development of scientific technology, the demand for energy storage equipment is increasing in modern society. Among the current energy storage devices, lithium-ion batteries (LIBs) have been widely used in portable electronics, handy electric tools, medical electronics, and other fields owing to their high energy density, high power density, long lifespan, low self-discharge rate, wide operating temperature range, and environmental friendliness. However, in recent years, with rapid development in various technological fields, such as mobile electronics and electric vehicles, the demand for batteries with much higher energy densities than the current ones has been increasing. Hence, the development of LIBs with a high energy density, prolonged cycle life, and high safety has become a focal interest in this field. To achieve the above objectives, it is important to strategically use novel anode materials with relatively high specific capacities. At present, artificial graphite is commonly used as an anode material for commercialized traditional LIBs, which can only deliver a practical capacity of 360–365 mAh·g^-1. Therefore, LIBs using graphite anodes have limited room for improvement in energy density. In the past two decades, considerable efforts have been devoted to silicon-based anode materials, which belong to the same family as carbon. To date, common silicon anode materials primarily include nano-silicon (nano-Si), silicon monoxide (SiO), suboxidized SiO (SiO_x), and amorphous silicon metal alloy (amorphous SiM). Among them, SiO has attracted the most attention for use as a negative electrode material for LIBs. As an anode for lithium-ion batteries (LIBs), silicon monoxide (SiO) has a high specific capacity (~2043 mAh·g^-1) and suitable charge (delithiation) potential (< 0.5 V). In addition, with the abundance of its raw material resource, low manufacturing cost, and environmental friendliness, SiO is considered a promising candidate for next-generation high-energy-density LIBs. Based on the testing of existing commercialized SiO materials, the reversible specific capacity of pure SiO can reach 1300–1700 mAh·g^-1. However, when acting as the anode for LIBs, SiO undergoes a severe volume change (~200%) during the lithiation/delithiation process, which can result in severe pulverization and detachment of the anode material. Meanwhile, lithium silicate and lithium oxide are irreversibly formed during the initial discharge–charge cycle. Moreover, the electrical conductivity of SiO is relatively low (6.7 × 10^-4 S·cm^-1). These shortcomings seriously impact the interfacial stability and electrochemical performance of SiO-based LIBs, leading to a low initial Coulombic efficiency and poor long-term cycling stability, which has significantly restricted its commercial application. In recent years, substantial efforts have been made on structural optimization and interfacial modification of SiO anodes. However, there is still a lack of a more comprehensive summary of these important developments. Therefore, this review aims to introduce the research work in this area for readers interested in this emerging field and to summarize in detail the research work on the performance optimization of SiO in recent years. Based on the structural characteristics of the SiO anode material, this review expounds the main challenges facing the material, and then summarizes the structural and interfacial modification strategies from the perspectives of SiO structure optimization, SiO/carbon composites, and SiO/metal composites. The methods and their features in all the studies are concisely introduced, the electrochemical performances are demonstrated, and their correlations are compared and discussed. Finally, we propose the development of the structural and interfacial optimization of the SiO anode in the future.

With the excessive exploitation and utilization of conventional fossil fuels such as coal, petroleum, and natural gas, the concentration of carbon dioxide (CO₂) in the atmosphere has increased significantly, leading to serious greenhouse effect. The electrocatalytic conversion of CO₂ to liquid fuels and value-added chemicals is one of ideal strategies, considering the atomic economy and artificial carbon circle. Moreover, this process can be driven by renewable energy (solar, wind, tidal power, etc.), thus achieving efficient clean-energy utilization. Electrocatalytic CO₂ reduction (ECR) can be carried out under ambient conditions, yielding diverse products such as C₁ (carbon monoxide, methane, methanol, formic acid/formate), C₂ (ethane, ethanol, ethylene, acetic acid), and C₂₊ (propyl alcohol, acetone, etc.). However, it faces some challenging problems such as high overpotential on electrodes, the poor selectivity of C₂ and C₂₊ products, the severely competitive hydrogen evolution reaction and the stability in the practice. The rational design and construction of highly active electrocatalysts with low cost, high selectivity, and robust stability are key to these issues. Recently, graphene-based materials have attracted significant attention owing to the following attributes: (1) robust stability in electrochemical environments; (2) tailorable atomic and electronic structures, leading to tuned catalytic activity; (3) adjustable dimensions and hierarchical porous structure, large surface area, and number of active sites; and (4) an excellent conductivity coupled with active, well-defined materials, synergistically enhancing the electrocatalytic activity in the ECR. In this review, recent progress in graphene-based electrocatalysts for ECR is summarized. First, ECR fundamentals, such as reaction routes, products, electrolyzers (e.g., H-cell electrolyzers, flow-cell electrolyzers, and membrane electrode assembly cells), electrolytes (e.g., inorganic electrolytes, organic electrolytes, and solid-state electrolytes), and evaluation parameters of ECR performance (e.g., faradaic efficiency, onset potential, overpotential, current density, Tafel slope, and stability) are briefly introduced. The methods for making graphene-based catalysts for ECR are outlined and discussed in detail, including in situ or post-treatment doping, surface functionalization, microwave-assisted synthesis, chemical vapor deposition, and static self-assembly. The relationships between the graphene structures, including the point/line defects, the surface functional groups (e.g., -COOH, -OH, C-O-C, C＝O, C≡O), heteroatom-doping configurations (e.g., pyridinic N, graphitic N, and pyrrolic N, and oxidized pyridinic N), metal single-atom species (e.g., Fe, Zn, Ni, Cu, Co, Sn, Mo, In, Bi), surface/interface properties, and catalytic performance are highlighted, shedding light on the design principles for efficient yet stable carbon-based catalysts for ECR. Finally, the opportunities and perspectives of graphene-based catalysts for ECR are outlined.

G-rich DNA sequences can transform into G-quadruplexes (G4s) in the presence of metal ions. Based on the structural switches, G4 has been recognized as an attractive signal-transducing element for constructing colorimetric, electrochemical, and fluorescent sensing platforms capable of recognizing ions, small biological molecules, proteins, and even cells. For fluorescent sensing platforms, fluorescent small molecules (FSMs) specifically binding with G4s, such as crystal violet (CV), protoporphyrin IX (PPIX), zinc protoporphyrin IX (ZnPPIX), and Thioflavin T (ThT), are usually applied as fluorescent signal readout probes. It was noticed that the binding affinity of FSM with G4 is highly dependent on G4 morphologies because G-rich DNA sequences can fold into multiple G4 conformations, such as parallel, antiparallel, or hybrid. For example, CV only binds with antiparallel G4, PPIX or ZnPPIX preferentially interacts with parallel G4, and ThT displays high affinity for hybrid G4. Furthermore, the binding affinity of FSMs with G4 is also dependent on co-existing ions and ion concentrations, especially elevated Na⁺ level (140 mmol·L^-1). It is the reason why the performance of G4-based sensors in biological and environmental samples is decreased with different extents. Therefore, how to design G-rich DNA sequences to generally achieve FSMs specifically binding with G4, which is independent of G4 morphologies and co-existing Na⁺ and Na⁺ concentrations remains a challenge. In this study, a simple G-rich DNA sequence (thrombin binding aptamer, TBA) flanked by 10-mer single-stranded DNA at the 3' and 5' termini (TBA-10 bp) is designed. In the presence of K⁺, TBA transforms into antiparallel G4 (K⁺-TBA) and TBA-10 bp transforms into antiparallel K⁺-TBA flanked by fully hybridized double-stranded DNA (ds-DNA) (K⁺-TBA-10 bp). Actually, ThT cannot effectively bind with antiparallel K⁺-TBA. Compared with K⁺-TBA, upon K⁺-TBA-10 bp binding with ThT, ThT emission fluorescence increased by 100-fold. Importantly, the binding affinity improved by 1000-fold, which is independent of co-existing Na⁺ and Na⁺ concentrations (5-140 mmol·L^-1). Integrated with UV-Vis spectroscopy, fluorescent spectroscopy, and circular dichroism spectroscopy, it is believed that ThT can specifically and efficiently imbed in the junction between K⁺-TBA and ds-DNA. To corroborate the binding mode, TBA in TBA-10 bp is substituted by other G-rich DNA sequences transforming into parallel and antiparallel G4 in the presence of K⁺, respectively. The resulting improved ThT emission fluorescence indicated that such a specific binding mode generally improved the binding affinity of FSMs with G4. Our findings provide new insights into the improvement of the binding affinity of FSMs and G4, and reveal potential biochemical and bioanalytical applications of G4.

Graphene is a 2D nanocomposite that has been gaining popularity in the research community in recent years. It is light weight with high tensile strength and excellent electrical conductivity. While graphene nanosheets are typically assembled into macroscopic nanocomposites, their beneficial properties may degrade from the aggregation of nanosheets owing to the weak interfacial interactions caused by random orientation and many other obstacles. Thus, finding an effective way to assemble the graphene nanosheets while not impacting its intrinsic properties is challenging. In nature, live organisms have always assembled numerous nanomaterials into high-performance nanocomposites. For example, nacre is composed of aragonite nanoplatelets and biopolymers such as protein and chitin. The aragonite nanoplatelets with a 95% volume fraction are stacked into a layered structure and "glued" together by biopolymers based on the "brick-and-mortar" architecture. The fracture toughness is 3000 times higher than natural aragonite minerals owing to the "extrinsic toughening mechanism" from the crack deflection and bridging in the "brick-and-mortar" architecture. We propose a nacre-inspired layered structure in graphene-based nanocomposites with two complementary strategies: constructing nacre-like and inverse nacre-like structures. This paper first introduces the structure and toughening mechanism of nacre and clarify the advantages of a bioinspired strategies. Then, some of the recent work on nacre-inspired graphene-based multifunctional nanocomposites is discussed. To construct the nacre-like structure, we fabricated graphene-based fibers and membranes with graphene as the main component. The nacre-like graphene-based nanocomposites have excellent tensile strength and toughness due to the synergistic effects from interfacial interactions and building blocks. It also demonstrated high electrical conductivity, which makes it suitable for electromagnetic interference shielding or supercapacitors. We also fabricated inverse nacre-like graphene-based nanocomposites with a small amount of graphene. The inverse nacre-like graphene-based nanocomposites has a layered structure and exhibited the "extrinsic toughening mechanism" seen in nacre. Consequently, the inverse nacre-like graphene-based nanocomposites possesses high fracture toughness that pushes the limit of "mixing rule". With the addition of graphene, the inverse nacre-like nanocomposites are suitable for use in many applications such as electrical conductivity, electrical heating, temperature measurement and many other functions. Finally, our study summarizes the strategies to overcome the obstacles we encountered during the assembly process to construct both the nacre-like and inverse nacre-like structures that were based on graphene. Some of the challenges we encountered include the small sample size, the quality of graphene nanosheets and developing hierarchical assembly techniques. The upcoming trends in nacre-inspired graphene-based multifunctional nanocomposites will also be discussed.

Rechargeable aqueous Zinc-ion batteries (ZIBs) have emerged as potential energy storage devices due to their high energy density, low cost, and safety. To date, numerous cathodes based on manganese dioxide, vanadium dioxide, and polyanionic compounds have been reported. Among them, MnO₂ cathodes are particularly desirable candidates for commercialization owing to their tunnel structure and affordability. In particular, the parasitic reaction of Mn-based cathodes in alkaline batteries can be suppressed in mild aqueous electrolytes, resulting in enthusiasm for the development of rechargeable Zn||MnO₂ batteries. Even though various MnO₂ phases have been reported as hosts for Zn²⁺/H⁺ insertion, MnO₂ crystal structures undergo significant, irreversible transformations during cycling, which is a major challenge in Zn||MnO₂ batteries. In addition, the tunnel structure can collapse under the insertion of the hydrated cation resulting in Mn²⁺ dissolution into the electrolyte and significant loss in capacity over long cycling periods. The MnO₂ cathode also has low intrinsic electronic conductivity due to the large charge transfer resistance, which limits the diffusivity of divalent ions. Despite the achievements made in the field of ZIBs so far, designing active materials and ZIBs systems to meet commercial requirements is a significant challenge. In this study, we report the preparation of polypyrrole-wrapped MnO₂/carbon nanotubes (PPy@MnO₂/CNT) as composite cathodes for aqueous ZIBs. A combination of design strategies was used to increase structural stability and improve electronic conductivity, including increased electrode/electrolyte interaction by using nano-sized structures, shortened diffusion pathways through multistage composites, and enhanced electrical conductivity with conductive composites. The three-dimensional (3D) structured PPy/CNT network can facilitate mass and charge transport during the charge and discharge processes. The structure of MnO₂ wrapped by polypyrrole effectively prevents the dissolution of MnO₂. Thus, the assembled Zn||MnO₂ batteries, using PPy@MnO₂/CNT composite cathodes, exhibit a high capacity of 210 mAh·g^-1 at 1 A·g^-1, and achieve 85.7% capacity retention after 1000 charge/discharge cycles. Moreover, a high specific capacity of 100 mAh·g^-1 could be maintained at 2 A·g^-1, exhibiting excellent kinetic performance. The assembled quasi-solid Zn//MnO₂ battery, benefiting from the xanthan gum electrolyte and flexible CNT film, possesses intrinsic safety, bending resistance, and high potential in wearable applications.

Perovskite solar cells (PSCs) attract much attention for their high efficiency and low processing cost. Power conversion efficiencies (PCEs) higher than 25% have been reported in literature, demonstrating the excellent application prospect of PSCs. In general, the crystallinity and the film composition of perovskite thin films are significant factors in determining device performance. Much effort has been made to control the growth process of perovskite films through the use of additives, passivation layers, special atmosphere treatments, precursor regulation etc. Among these methods, precursor solvent engineering is a simple and direct way to control the perovskite quality, but the controllability of components through solvent engineering is still difficult and has not yet been reported. Herein, we report the controlled formation of PbI₂ and PbI₂ with dimethyl sulfoxide (DMSO) nano domains through precursor solvent engineering. In particular, tuning the solvent content of the dimethyl sulfoxide: 1, 4-butyrolactone: N, N-dimethylformamide (DMSO : GBL : DMF) in the perovskite precursor solution, controlled the content of PbI₂ and PbI₂(DMSO) domains. Due to the lower boiling point and weaker coordination of DMF relative to DMSO, part of methylammonium iodide (MAI) would escape from the wet films during the evaporation process. Therefore, the PbI₂(DMSO) can't completely convert to perovskite crystals and is retained in the final films as residual PbI₂(DMSO) domains. Both UV-vis absorption spectrum and XRD spectrum confirmed the existence of PbI₂ and PbI₂(DMSO) domains. Importantly, the content of PbI₂(DMSO) was controllable by simply changing the relative proportion of DMF. With an increase in the DMF content, the residual PbI₂(DMSO) domains gradually increase. In addition, the influence of PbI₂ and PbI₂(DMSO) domains on the device performance was systematically investigated. The formation of PbI₂(DMSO) domains caused a decrease in external quantum efficiency (EQE) of the device over 300–425 nm, and consequently decreased the device performance. That was because the PbI₂(DMSO) domain has strong absorption over 300–425 nm. Therefore, the PbI₂(DMSO) domains would absorb the photons over 300–425 nm prior to the perovskite, however the photons absorbed by the PbI₂(DMSO) domains are not converted into the photocurrent. Thus, the perovskite solar cell containing PbI₂(DMSO) showed an EQE loss over 300–425 nm in the EQE spectra. This work provides a simple method to control the components, especially the content of the PbI₂(DMSO) domains, in perovskite films through regulating the precursor solvent. Additionally, this work revealed a PbI₂(DMSO) domain related EQE loss phenomenon, highlighting the importance of controlling this component.

Sustainable freshwater supply is a grave challenge to the society because of the severe water scarcity and global pollution. Seawater is an inexhaustible source of industrial and potable water. The relevant desalination technologies with a high market share include reverse osmosis and thermal distillation, which are energy-intensive. Capacitive deionization (CDI) is a desalination technology that is gaining extensive attention because of its low energy consumption and low chemical intensity. In CDI, charged species are removed from the aqueous environment via applying a voltage onto the anode and cathode. For desalination, Na⁺ and Cl^- ions are removed by the cathode and anode, respectively. With the boom in electrode materials for rechargeable batteries, the Na⁺ removal electrode (cathode) has evolved from a carbon-based electrode to a faradaic electrode, and the desalination performance of CDI has also been significantly enhanced. A conventional carbon-based electrode captures ions in the electrical double layer (EDL) and suffers from low charge efficiency, thus being unsuitable for use in water with high salinity. On the other hand, a faradaic electrode stores Na⁺ ions through a reversible redox process or intercalation, leading to high desalination capacity.However, the Cl^- removal electrode (anode) has not yet seen notable development. Most research groups employ activated carbon to remove Cl^-, and therefore, summarizing Cl^- storage electrodes for CDI is necessary to guide the design of electrode systems with better desalination performance. First, this review outlines the evolution of CDI configuration based on the electrode materials, suggesting that the anode and cathode are of equal importance in CDI. Second, a systematic summary of the anode materials used in CDI and a comparison of the characteristics of different electrodes, including those based on Ag/AgCl, Bi/BiOCl, 2-dimensional (2D) materials (layered double hydroxide (LDH) and MXene), redox polymers, and electrolytes, are presented. Then, the underlying mechanism for Cl^- storage is refined. Similar to the case of Na⁺ storage, traditional carbon electrodes store Cl- via electrosorption based on the EDL. Ag/AgCl and Bi/BiOCl remove Cl^- through a conversion reaction, i.e., phase transformation during the reaction with Cl^-. 2D materials store Cl^- in the space between adjacent layers, a process referred as ion intercalation, with layered double hydroxide (LDH) and MXene showing higher Cl^- storage potential. Redox polymers and electrolytes allow for Cl^- storage via redox reactions. Among all the materials mentioned above, Bi/BiOCl and LDH are the most promising for the construction of CDI anodes because of their high capacity and low cost. Finally, to spur the development of novel anodes for CDI, the electrodes applied in a chlorine ion battery are introduced. This is the first paper to comb through reports on the development of anode materials for CDI, thus laying the theoretical foundation for future materials design.

Zirconium alloys are often used to fabricate nuclear fuel cladding and other structural materials because of their low thermal neutron absorption cross section, satisfactory corrosion resistance, and decent mechanical properties. The oxidation rate and hydrogen-absorption fraction of zirconium alloys can be reduced by adding moderate amount of Nb to them, and the corrosion resistance of zirconium alloys can be improved as well. Although the corrosion resistance of zirconium alloys has been widely recognized, the in situ study of zirconium alloys in conditions that resemble real oxidative-corrosion environments has still been a challenging subject. The initial oxidation behavior of zirconium alloys might affect the subsequent generation of oxides in the form of the element valence and type of surface oxides changes, resulting in the long-term corrosion-behavior changes. In addition, the reaction mechanism of Nb in zirconium alloys is still controversial. To investigate the influence of the alloy composition and environmental conditions on the initial oxidation behavior of zirconium alloys, in situ initial oxidation experiments were performed on two different Zr alloys in a near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) chamber. The samples were cut to the size of 12 mm × 3 mm, and the primary oxide film was removed via pickling, argon etching and annealing. Oxygen or water vapors with the pressure in the range of 1.3 × 10^-8-1.3 × 10^-1 mbar (1 mbar = 100 Pa) were gradually introduced into the NAP-XPS chamber after sample-surface cleaning. The experiment was repeated at room temperature (300 K) and 623 K. The results showed that both Nb-containing and Nb-free zirconium-alloy surfaces transitioned from a metallic state to various oxidation states during the initial oxidation process. The oxidation rates of both the alloys were lower in water vapors than those in oxygen. In the presence of water vapors or oxygen, both the alloys oxidized more slowly at room temperature than at 623 K. Compared with 1%Nb zirconium alloys, the Nb-free zirconium alloys were more easily oxidized and had a denser oxide layer, in the oxygen atmosphere at 623 K. To some extent, the presence of Nb would reduce the adsorption capacity of oxygen atoms. The oxidation rate of 1%Nb zirconium alloy was quick at room temperature and also at low water vapor pressures at 623 K; Nb promoted the formation of OH^- at the surface. Under the high pressure vapor atmosphere at 623 K, the Nb-free zirconium alloys were more prone to be oxidized; Nb diffused to the surface at high temperatures and inhibited the breaking of the OH^- bond; however, the surfaces of both the samples could not be completely oxidized in a short time.

Graphene wafers have emerged in response to the increasing demand of wafer-scale two-dimensional materials and high-performance on-chip devices in the field of integrated circuits, microelectromechanical systems, and sensors. Wafer-scale graphene films display great application potential, owing to their atomic layer thickness, excellent thermal and electrical conductivity, and compatibility with wafer-processing technology. Therefore, batch production of graphene wafers is exceedingly crucial. The chemical vapor deposition (CVD) method has attracted attention for the production of high-quality graphene wafers with high controllability, high compatibility, and low cost. Mature CVD manufacturing has been widely employed in the semiconductor industry to date, aiding in the industrialization of CVD graphene wafers and creating opportunities for graphene to enter the new era of nanoelectronics. The quality of graphene wafers has a significant impact on the subsequent device fabrication; hence, considerable efforts have been made to date to realize precise control over domain size, structural defects, and layer thickness during synthesis. In this study, we summarize the recent progress made in wafer-scale CVD graphene synthesis. Initially, we introduce the quality requirements of graphene wafers targeting various application scenarios, and propose the classification of graphene wafers. Single crystallinity is considered to be a key requirement for the graphene used in high-performance electronics and optoelectronics. We then review the recent CVD-derived graphene wafers with regard to substrate types (metal/nonmetal), highlighting the constrictions in graphene quality and corresponding synthetic solutions. Batch synthesis of graphene wafers is further discussed. The significant role of flow dynamics in the up-scaling process is emphasized, followed by relevant experimental instances based on computational fluid dynamics simulations. Finally, strategies for obtaining graphene wafers are overviewed, with the proposal of future perspectives. This study focuses on three areas: (1) Application requirements for the quality of graphene wafers, including target substrate types and as-grown graphene features (chemical stability and electrical and thermal properties), (2) CVD strategies of graphene wafers: As for the growth scenarios on metal substrates, controllable preparation of bilayer/multilayer graphene and the elimination of structural defects remain challenging. With respect to the synthesis over nonmetal wafers, concrete examples highlighting the epitaxial growth on a crystalline substrate and tailorable growth on a surface-reconstructed substrate are summarized. (3) Batch synthesis of graphene wafers: CVD routes for scalable production are explored.

Although there has been great progress, the commercialization of proton exchange membrane fuel cells (PEMFCs) is still hindered by high cost due to the use of Pt catalysts. Furthermore, structural improvement of the catalyst layers is limited by inadequate studies of the ultrathin perfluorosulfonic acid ionomer (e.g., Nafion ionomer) film in the catalyst layers. During the preparation of the catalyst ink, the dispersion solvent affects the morphology of Nafion ionomers, which affects the microstructure and proton conduction behavior of the Nafion thin film wrapped on the surface of the catalyst particles after the catalyst layer is formed. To simulate the aggregation of ionomers in the catalyst layer, a self-assembly technology was used to obtain nanoscale Nafion thin films with precise and controllable thickness on a SiO₂ model substrate. The proton conductivity and microstructure of the Nafion thin films were obtained through electrochemical impedance spectroscopy and a series of micro-characterization methods. Furthermore, the relationship between proton conduction behavior within ultrathin Nafion films and colloidal morphology in Nafion solution was studied using different organic solvents. The goal was to explore and establish the microstructure model of nanoscale Nafion thin films through micro-characterization technologies, such as nuclear magnetic resonance and dynamic light scattering. It was found that at the nanoscale, Nafion thin films (~40 nm) result in low proton conductivity; an order of magnitude lower than that of bulk membranes (~10–100 μm). However, replacing iso-propanol with n-butanol (which has a lower dielectric constant) as the dispersion media of the Nafion ionomer improved the proton conductivity of the Nafion thin films. This is because Nafion in solvents with a lower dielectric constant possesses higher main chain solubility and mobility. Thus, Nafion molecules more easily aggregate into large rod-shaped micelles, which is beneficial to the construction of proton conduction channels after the self-assembly process. Furthermore, the electrostatic force between Nafion aggregates and the substrate in solvents with lower dielectric constant is smaller. This means more sulfonic groups are involved in the formation of proton conduction channels that in turn improve the proton conductivity of the Nafion thin film. In general, Nafion in solvents with lower dielectric constant leads to a structure that can facilitate proton conduction. This study provides guidance for optimizing the structure of ultrathin Nafion films and improving the proton conduction in the catalyst layers of PEMFCs.

With the rapid development of the functional applications of portable and wearable electronic products (such as curved smartphones, smartwatches, laptops, and electronic skins), there is an urgent need to fabricate flexible, lightweight, and highly efficient energy storage devices that can provide sufficient power support. Flexible supercapacitors with high power density, high charging/discharging rates, wide operating temperature ranges, low maintenance consumption, and a long cycling lifespan can be integrated with smart wearable electronic products to provide power support. The conventional preparation method for the electrodes of flexible supercapacitors involves directly coating the active materials on flexible substrates. However, inactive materials such as the substrates and binders occupy a large volume and contribute notably to the weight of flexible electrodes, which is unsuitable for highly integrated flexible electronic devices. Owing to its unique characteristics, including large theoretical specific surface area, high electrical conductivity, excellent mechanical flexibility, good chemical stability, and ease of film processing, graphene has been widely used as an electrode material for flexible supercapacitors. The graphene film is a macrostructure with graphene nanosheets as the main structural units. As opposed to conventional flexible electrodes containing non-electrochemical active components such as collectors, conductive agents, and binders, graphene film electrodes are considered highly promising electrode materials for flexible supercapacitors because of their light weight and robust mechanical properties. However, the inevitable aggregation of graphene during electrode preparation creates ''dead volume'' in the film electrodes, where the electrolyte cannot reach, further limiting the specific capacitance. In this review, we review the recent research on graphene films used for flexible supercapacitors, with emphasis on the assembling methods for graphene films, regulation of the graphene units, and their electrochemical performance. First, simple preparation methods for graphene films are introduced: vacuum-assisted self-assembly, blade coating, pressing aerogel, wet spinning, and interfacial self-assembly. Second, two major strategies for structural control and surface modification of the graphene units are described in detail: (1) structural control can transform the two-dimensional graphene nanosheets into defect graphene, which not only weakens the van der Waals force and π–π bond interactions between the nanosheets, but also leads to the formation of three-dimensional conductive networks and ion transport channels during the assembly process; (2) surface modification, which can suppress the agglomeration of graphene nanosheets by introducing heteroatoms and reactive functional group molecules, while improving their electrical conductivity and wettability, and introducing pseudocapacitance. Finally, the persisting challenges and future development of the commercial applications of graphene films are discussed.

Lithium-sulfur batteries are considered to be one of the most promising new-generation energy storage devices, owing to their ultra-high theoretical energy density and the merits of sulfur cathodes, which include natural abundance, low cost, and no toxicity. However, the commercial application of lithium-sulfur batteries is still subject to various intractable challenges. First, the insulation of sulfur and its solid discharge products (Li₂S₂/Li₂S) leads to low utilization of the active materials. Second, the cathode suffers from an 80% volume expansion after the discharge process, which adversely affects its structural stability. Finally, intermediary lithium polysulfides can easily dissolve into the electrolyte, which can trigger the "shuttle effect." This results in the loss of active materials, fast capacity fading, and low Coulombic efficiency. Graphene has garnered significant interest as a host material to accommodate sulfur for high-performance lithium-sulfur battery. A graphene host featuring a high specific surface area, excellent conductivity, and excellent mechanical stability can ensure a good electrical contact between the sulfur species and the current collector and withstand the volumetric strain of the electrode during cycling. Unfortunately, lithium polysulfides are still prone to escape from cathodes owing to the open two-dimensional (2D) plane structure of graphene sheets. To address this issue, various graphene-based materials with unique structures and chemical compositions have been trialed as sulfur hosts. In this review, we summarize research progress regarding three-dimensional (3D) graphene, graphene with modified surface chemistry, graphene-based composites, and graphene-based flexible materials as sulfur hosts for lithium-sulfur batteries. Furthermore, we analyze the challenges of applying graphene host materials in high-performance lithium-sulfur batteries. This review is mainly divided into four parts: (1) 3D graphene materials as sulfur hosts: the interconnected 3D porous network structure assembled from 2D graphene sheets provides a half-enclosed cavity to accommodate sulfur and its discharge products, which can inhibit the diffusion of lithium polysulfides to a certain extent. (2) Graphene materials with modified surface chemistry as sulfur hosts: hydrophilic surface functional groups and doped non-metal or metal heteroatoms on graphene can chemically adsorb polar lithium polysulfides. (3) Graphene-based composites as sulfur hosts: in various graphene-based composites, graphene usually functions as a conductive and flexible substrate. Other components, such as other types of carbon or metal compounds, can play an important role in restricting lithium polysulfides and propelling their reaction kinetics. (4) Flexible graphene-sulfur electrodes: the excellent flexibility and conductivity of graphene endowed it and its composites with a broad range of prospective applications regarding flexible lithium-sulfur batteries.

Resistive switching devices have the advantage that the resistance can be repeatedly regulated between two or more resistance states. As a new resistive switching device, a memristor has abundant resistance states that can be continuously tuned. In recent years, memristors have been extensively studied for emerging nonvolatile memories and in the construction of neuromorphic systems owing to their simple two-terminal structure, high integration, and low operating voltage compared with those of traditional metal-oxide-semiconductor field-effect transistors. However, their application is limited owing to their relatively poor reliability. Recently, several studies have shown that two-dimensional materials such as graphene oxide can optimize the memristor performance. A new two-dimensional material, MXene, also exhibits special mechanical and electrical properties that show promise for use in memristors owing to its two-dimensional layered structure similar to that of graphene. MXene is a two-dimensional transition metal carbide/nitride of the form M_n+1X_n, where M is an early transition metal and X is carbon or nitrogen. Its other characteristics such as hydrophilic surfaces and ultrahigh metal conductivity (6000–8000 S·cm^-1) have been studied, and it has been applied to energy storage devices and electronic devices such as supercapacitors and secondary batteries. However, the application of MXene in resistive devices has been rarely investigated, especially for memristors. In this study, we prepared Ti₃C₂ powder by etching layered compounds of Ti₃AlC₂ with a mixture of HCl and HF. Next, Ti₃C₂ film was introduced into the memristor structure by spin-coating. The physical characteristics of Ti₃C₂ were investigated and analyzed by X-ray diffraction and scanning electron microscopy, and a memristor with Cu/Ti₃C₂/SiO₂/W structure was fabricated. In this structure, Ti₃C₂ and SiO₂ were introduced as resistive layers, and related electrical properties were investigated. Under dual DC voltage sweeping, the typical switching characteristic curves of the memristor were measured. Moreover, the repeatability and stability of high- and low-resistance states were investigated and analyzed, respectively. The experimental results show that the device can maintain stable high- and low-resistance states for > 10⁴ s during 100 dual-voltage sweeping cycles. In addition, the device can be regulated by a pulse voltage and realize typical paired-pulse facilitation that is similar to biological synapses. This work proved that the Cu/Ti₃C₂/SiO₂/W memristor has huge potential for application in the construction of emerging memory devices and artificial neuromorphic systems.

High-performance rechargeable lithium ion batteries have been widely applied in electrochemical energy storage fields, such as, energy storage grids, portable electronic devices, and electric vehicles (EVs). However, the energy density of lithium ion batteries needs to be increased, and the cost of battery materials could be further reduced for wider commercial applications. An Ni-rich cathode, LiNi_xMn_yCo_1-x-yO₂ (x > 0.8), with high specific capacity is the most promising material for next-generation Li-ion batteries. LiNi_xMn_yCo_1-x-yO₂ (x > 0.8) contains three transition metal elements, Ni, Mn, and Co, respectively. The role of Ni²⁺ is to provide high capacity for recharge The role of Mn⁴⁺ is to stabilize the lattice structure during charging-discharging cycling. Crucially, the role of Co³⁺ in Ni-rich materials is to improve the electrical conductivity and inhibit cation disorder in the lattice during electrochemical cycling. However, Co is both in shortage and expensive, which limits its worldwide commercial application. This work investigates substituting Co with other abundant and cheap transition metals. Transition metal ions Cr³⁺, Cd²⁺, and Zr⁴⁺ can replace Co³⁺ in Ni-rich cathode materials. LiNi_0.8Cr_0.1Mn_0.1O₂, LiNi_0.8Cd_0.1Mn_0.1O₂, and LiNi_0.8Zr_0.1Mn_0.1O₂ were synthesized by a co-precipitation method. Zr was found to be the best candidate for replacing Co in Ni-rich cathode materials. This study investigated Zr⁴⁺-doped Co-free Ni-rich materials. Initially, a carbonate co-precipitation process was used to synthesize Ni_0.8Zr_0.1Mn_0.1CO₃. This is due to that Zr³⁺/Zr⁴⁺ ions are not precipitated in the strong alkali solution, and the pH during hydroxide co-precipitation and carbonate co-precipitation processes are approximately 11 and 8, respectively. Therefore, the carbonate co-precipitation synthesis method was chosen. Ni_0.8Zr_0.1Mn_0.1CO₃ was synthesized by carbonate co-precipitation at pH = 7.6, 7.8, 8.0, and 8.2. After electrochemical analysis, pH = 7.8 was identified as the optimal value. The next stage of the research involved completing an electrochemical performance comparison on two lithium sources. The following lithium sources were added to the precursor; LiOH·₂O, and a 1:1 mixture of LiOH·₂O and Li₂CO₃. The lithium source with the 1:1 mixture, exhibited better performance for the Ni-rich cathode, LiNi_0.8Zr_0.1Mn_0.1O₂. In this study, the ideal doping amount of Zr in Ni-rich materials was 0.05. In conclusion, by careful control of co-precipitation pH and Li source, the Zr doped cobalt free Ni-rich cathode LiNi_0.85Mn_0.1Zr_0.05O₂ delivered a discharge capacity of 179.9 mAh·g^-1 at 0.2C. This was achieved between the voltage range of 2.75-4.3 V, with an 80 cycle capacity retention of 96.52%.

Metal oxide semiconductor (MOS) gas sensors have been widely used in military and scientific research, as well as various industries; this is because of the unique advantages of MOS gas sensors including their small size, low power consumption, high sensitivity, and good silicon chip compatibility. However, the poor selectivity of MOS sensors has restricted their potential application in the Internet of Things (IoT) era. In this paper, progress in the research addressing the selectivity issues of MOS sensors is reviewed, and three strategies for selective MOS sensors, and performance improvements of MOS, e-nose, and thermal modulation, are introduced. Research on the performance improvements of MOS-sensitive materials provides an important guarantee for fast and accurate identification of trace gas molecules. The e-nose system adopts an array of sensors with distinct surface chemical properties; more "features" of volatile organic compound (VOC) molecules can be extracted by enlarging the number of sensor arrays, providing a "many-to-one" or "many-to-many" approach to discriminate VOC gas molecules via pattern recognition/machine learning algorithms. For thermal modulation technology, the working temperature of the sensor is intentionally swept during one measurement cycle, and the dynamic response signals of the sensor to different VOC gases under a given temperature mode are tested. Combined with signal processing and pattern recognition/machine learning, the "one-to-many" recognition of VOC gas molecules is realized by a single MOS sensor. Principal component analysis (PCA), linear discriminant analysis (LDA), and neural network (NN) pattern recognition/machine learning algorithms are compared in this review. Among them, the LDA algorithm based on supervised learning can be used as a signal dimension reduction or pattern recognition method. It is mainly applicable to the gas identification and classification of small datasets of VOC gas molecules. LDA is superior to PCA (based on unsupervised learning) in identifying and classifying VOC gas molecules. Compared with the LDA algorithm, an artificial neural network (ANN) based on the back-propagation algorithm, as a highly robust machine learning classification model, has the potential to process large datasets and realize the classification and identification of multiple kinds of VOC gases. Finally, the deep learning algorithm of convolutional neural networks (CNNs), with the performance of data dimension reduction, feature extraction, and robust identification, is expected to be applied in the field of VOC gas identification. Based on the performance improvement of MOS, a combination of multiple modulation methods and array technology, as well as the latest developments of deep learning algorithms in the artificial intelligence (AI) field, will greatly enhance the VOC molecular recognition capability of nonselective MOS sensors.

Lithium-ion batteries are the most widely used energy storage device owing to their advantages such as high energy density, high cycle life, and low self-discharge rate. Because two-dimensional (2D) materials are commonly used as anode materials, the study of their lithiation behaviors is significant for improving the energy density and cycle life of batteries. Although some spectroscopic methods have been developed for studying the intercalation/deintercalation process of lithium in graphene, a new characterization technique that can directly investigate ion diffusion pathways at a microscale level would be beneficial to provide more detailed information on the mechanism of electrochemical reactions. It is an efficient solution to utilize the high spatial resolution of microscopic characterization to study the microscale electrochemical process. For this purpose, it becomes necessary to develop special specimens and setups that can undergo electrochemical experiments and are also compatible with microscopic characterization techniques. Herein, we developed a new planar micro-battery architecture on a SiO₂-coated silicon substrate that can be used to study the lithiation behaviors of various 2D materials using the micro-Raman mapping technique. In this planar micro-battery, the mechanically exfoliated few-layer graphene was used as the positive electrode, the thermal-evaporated lithium metal was employed as the negative electrode, and the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with lithium bis(trifluoromethane)sulfonimide was used as the electrolyte. The micro-battery was tested using the galvanostatic discharge method on a probe station in an argon glove box. The selected lab-on-chip solution makes the lithiation of graphene observable under the micro-Raman spectroscope with a high spatial resolution. Raman mapping was successfully performed and graphene G-band signals were observed. Based on the facts that a small amount of lithium intercalation in graphene induces a blueshift of its G-band, and a large amount of lithium intercalation induces the splitting of the G-band into G^- and G⁺, we can correlate the degree of lithiation in graphene with its G-band signals and thus monitor the lithium intercalation process on graphene in the planar micro-battery. The time-dependent lithium distribution in graphene at different discharge stages could be obtained by comparing the G-band Raman mapping images to the corresponding optical micrographs. On the basis of these analyses, it was found that lithium ions diffuse between the layers in graphene and terminate at the graphene fault. These results help us understand the diffusion process of lithium in the graphene electrode during discharge. Moreover, the as-developed micro-battery is compatible with more characterization methodologies, such as optical microscopy, electrical transport, and electron microscopy, providing a broad application platform.

Inorganic perovskite materials have gained considerable attention owing to their good thermal stability, high absorption coefficient, adjustable bandgap, and simple preparation. However, most inorganic perovskites are sensitive to water and need to be prepared under inert environments in a glove box, which increases their preparation cost. In this study, we used a simple one-step spin coating anti-solvent process to prepare CsPbI₂Br, which was then annealed in humid air (relative humidity < 35%) at 300 ℃ for 5 min with isopropanol as the anti-solvent. An inorganic perovskite solar cell with fluorine-doped tin dioxide/compact TiO₂/mesoporous TiO₂/CsPbI₂Br/hole transport materials/Ag structure was prepared. By varying the concentration of the mesoporous precursor, we controlled the thickness of mesoporous TiO₂ in order to investigate its effect on the properties of the perovskite films and devices. The X-ray diffraction (XRD) results confirmed the successful synthesis of CsPbI₂Br in humid air. Moreover, the thickness of the substrate affected the crystal growth orientation. The scanning electron microscopy results revealed that the thickness of the mesoporous titanium dioxide substrate affected the crystallization processing of CsPbI₂Br, resulting in the formation of compounds with different morphologies and phases. The ultraviolet-visible (UV-Vis) and photoluminescence spectra of the perovskite materials revealed that the substrate thickness affected their optical properties. With a decrease in the thickness of the mesoporous TiO₂ substrate, the bandgap of CsPbI₂Br increased slightly. At the substrate thickness of 145 nm, the defect density of state of CsPbI₂Br increased. At the optimum mesoporous titanium dioxide substrate thickness of 732 nm, the device showed the best power conversion efficiency of 8.16%. The electrochemical impedance spectroscopy measurements revealed that the devices prepared on thicker mesoporous layers showed better carrier extraction and transmission capabilities but higher interfacial charge recombination resistance, leading to a lower open-circuit voltage but higher current density. Thus, an increase in the thickness of the mesoporous substrate improved the photovoltaic performance of the devices. The stability of the CsPbI₂Br perovskite film improved with an increase in the mesoporous substrate thickness. The stability test results along with the UV-Vis and XRD analysis results showed that the perovskite film prepared on the 732 nm-thick substrate showed no significant structure change after being placed in humid air for 144 h. The stability of the perovskite solar cells was also investigated. The device with the 732 nm-thick substrate could maintain its original efficiency of 73% after exposure to air with relative humidity less than 35% for 72 h. Thus, inorganic perovskite solar cells could be successfully prepared in the humid air environment.

With the development of photovoltaic devices, organic-inorganic hybrid perovskite solar cells (PSCs) have been promising devices that have attracted significant attention in the fields of industrial and scientific research. Currently, the photoelectric conversion efficiency (PCE) of PSCs has been improved to 25.2%, and they are considered to be the primary alternative to silicon-based solar cells. However, the environmental stability of PSCs is unsatisfactory; they are prone to degradation under exposure to moisture, oxygen, elevated temperature, or even light illumination, which restricts their wide application in industrial production. Previous studies have elucidated that understanding the ultraviolet (UV)-induced degradation mechanism of organic-inorganic PSCs is of great importance for the improvement of light stability in PSCs. However, until now, there has been almost no comprehensive investigation on the decay process of PSCs under UV light illumination nor on the corresponding evolution of their microstructure. In this study, focused ion beam scanning electron microscopy (FIB-SEM) and aberration-corrected transmission electron microscopy (TEM) were used to comprehensively study changes in the performance and the evolution of the microstructure of PSC devices. The experimental results show that a built-in electric field developed under UV light illumination, which drove the diffusion of iodide ions (I^-) from the CH₃NH₃PbI₃ (MAPbI₃) layer to the hole transfer layer (HTL, Spiro-OMeTAD). Together with the photo-excited holes in the HTL, the I^- ions reacted with the Au electrode, and the Au atoms were oxidized into Au⁺ ions. Furthermore, Au⁺ ions preferred to diffuse across the HTL and the perovskite layer into the interface between the SnO₂ and MAPbI₃ layers. SnO₂ is known to be a good electron transfer layer (ETL), which should collect the photo-excited electrons to reduce the Au⁺ ions into metallic Au clusters; this is why the Au electrode was destroyed and Au clusters aggregated at the SnO₂-MAPbI₃ interface under the UV light illumination. Meanwhile, the Au clusters would accelerate the degradation of the perovskite. In addition, as the PSC performance declined (as determined by the PCE, open-circuit voltage (V_oc), and short-circuit current (J_sc)), the decomposition of tetragonal MAPbI₃ into hexagonal PbI₂ was observed at the interface between Spiro-OMeTAD and MAPbI₃, along with a widening of the grain boundaries in the perovskite layer. All of these factors play critical roles in the UV-induced degradation of PSCs. This is the first study to elucidate the light-induced migration of Au from the metal electrode to the interface between SnO₂/MAPbI₃, which reveals that the UV-induced degradation of PSCs may be mitigated by finding new ways to restrain the interdiffusion of Au⁺ and I^- ions.

With the increasing demand for safe high energy density energy storage systems, solid-state lithium metal batteries have attracted extensive attention. The solid electrolyte, which is expected to replace the traditional liquid organic electrolyte core in solid-state lithium metal batteries because of its excellent mechanical properties and non-flammability. Lithium-ion solid-state electrolytes can be categorized into two broad types: inorganic electrolytes and polymer electrolytes. Inorganic solid electrolytes have the advantages of high room-temperature ionic conductivity, wide electrochemical window, and high mechanical strength. However, their high brittleness, high solid-solid interface contact resistance, complex preparation process, and high cost make future development and practical applications challenging. In contrast to inorganic electrolytes, polymer electrolytes are easy to process and exhibit better flexibility and easy formation of a good, stable interface with lithium metal. However, solid polymer electrolytes still exhibit insufficient ionic conductivity at room temperatures compared with polymer solid electrolytes. Therefore, neither the inorganic electrolytes nor the polymer electrolytes alone can meet the requirements of high-performance solid-state lithium metal batteries. Recently, dispersing ceramic fillers (especially fast lithium-ion conductors) in a polymer matrix to integrate with composite polymer electrolytes has been developed as an effective strategy for enhancing room-temperature ionic conductivity, mechanical properties, and thermal stability of solid polymer electrolytes. Inorganic fillers do not only reduce the polymer matrix crystallization but also improve the lithium-ion conductivity by promoting the dissociation of lithium salts. The Lewis acid-base groups and oxygen vacancy at the surface of inorganic fillers can increase the migration number of lithium ions. Nevertheless, the effect of the percolation structure of inorganic fillers on the conductivity of organic-inorganic composite electrolytes should be discussed. It is believed that the organic-inorganic interface is the main reason for the significantly enhanced lithium-ion conductivity of composite electrolytes based on the percolation theory. In this paper, from the perspective of percolation structure design, we summarize the progress on high lithium-ion conductive organic-inorganic composite electrolytes with different dimensional-structured inorganic fillers. From one-dimensional filler to three-dimensional filler, the ionic conductivity of a composite electrolyte can be significantly influenced by the rational design and optimization of the percolation structure and orientation of the inorganic filler. Vertically aligned inorganic fillers provide optimal ion transport pathways in the polymer matrix, significantly improving the lithium-ion conductivity of the composite electrolytes. Furthermore, the advantages and disadvantages of the different percolation structures are compared and discussed objectively. Finally, future development trends of organic-inorganic composite electrolytes are discussed.

This paper, based on the 292nd "Shuang-Qing Forum, " introduces the scientific concept of "green carbon science" and summarizes the current research progress, challenges, and future opportunities for carbon-neutral science and technology in China. Furthermore, there is scientific discussion on the path to realizing this, key scientific problems, and future research focus on carbon-neutral science and technology. It may provide a reference from which the National Science Foundation of China (NSFC) can formulate an action plan and funding scheme for basic research on carbon neutrality as a next step.

The environmental behaviours of actinides and fission products have been highly concerned due to their potential risks to human beings after entering the body through inhalation or food chains. The chemical reactions of actinides and fission products at mineral-water interface are the most important factors influencing the sorption, diffusion, migration and other processes of actinides and fission products in natural environments. Therefore, it is of great importance to investigate the chemical behaviours of these radioactive elements or nuclides in terms of environmental safety, especially in the area of safety assessment for geological disposal of high level radioactive wastes. However, the chemical behaviours of nuclides at mineral-water interface are complex and the investigations at a molecular level are challenging. To understand the chemical behaviours of trivalent actinides An(Ⅲ) in depth, non-radioactive Eu(Ⅲ) is used as an analogue of An(Ⅲ) due to their similar ionic sizes and chemical characteristics. In this study, batch sorption experiments and spectroscopic characterization methods were used to study the surface sorption species of Eu(Ⅲ) on montmorillonite and possible sorption mechanisms. We studied the effects of solid-liquid ratio, contacting time, ionic strength, pH, carbonate and phosphate on Eu(Ⅲ) sorption on montmorillonite. Our results indicated that the sorption percentage of Eu(Ⅲ) on montmorillonite was low in the range of pH 3.0 to 6.0, and much higher in the range of pH 7.0 to 10.0. The increase of ionic strength inhibited the sorption of Eu(Ⅲ) at low pH values, suggesting that the sorption of Eu(Ⅲ) on montmorillonite was mainly outer-sphere complexation in low pH conditions. Based on the results of fluorescence analysis, we can conclude that the sorption of Eu(Ⅲ) on montmorillonite is mainly outer-sphere complexation in low pH conditions, inner-sphere complexation in neutral pH conditions and surface induced precipitations in high pH conditions. Furthermore, we studied the sorption behaviours of Eu(Ⅲ) not only in montmorillonite/Eu(Ⅲ) binary system but also in montmorillonite/Eu(Ⅲ)/anion ternary system. Our results indicated that carbonate and phosphate could also influence the sorption of Eu(Ⅲ). Carbonate did not have an obvious influence on the sorption amount of Eu(Ⅲ), but it helped to change the surface sorption species of Eu(Ⅲ) on montmorillonite in high pH conditions. As for phosphate, although the sorption of phosphate onto montmorillonite was very weak, it could significantly enhance the sorption of Eu(Ⅲ) on montmorillonite. Because there were no reference data about fluorescence lifetime of Eu(Ⅲ)-phosphate species, we did XPS measurements and phosphate sorption experiments to find out the reason for phosphate enhancing effect. Our results proved that Eu(Ⅲ) precipitated as EuPO₄ on the surface of montmorillonite resulting in the enhancement of Eu(Ⅲ) sorption. This work is expected to provide a deeper understanding of the chemical behaviours of trivalent actinides An(Ⅲ) at mineral-water interface and predict the migration of An(Ⅲ) in the environment.

The acid properties of SAPO-34 molecular sieves (MSs), including the strength and density of Brönsted acids, have attracted enormous attention in past decades because of the excellent performance of SAPO-34 in industrial processes such as the methanol-to-olefins (MTO) process and the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). Currently, pure-phase SAPO-34 MSs with different Si contents can be easily obtained by utilizing multifarious organic structure-directing agents (OSDAs). However, the resulting SAPO-34 MSs have different acid properties, which may affect their catalytic performance. Hence, correlating the acid properties with the OSDAs and Si contents is of significance to synthesize SAPO-34 MSs with the desired properties. Herein, the acid properties of four series of SAPO-34 MSs with varying Si contents synthesized using tetraethylammonium hydroxide (TEAOH), diisopropylamine (DIPA), n-butylamine (nBA), and morpholine (MOR) as the OSDAs were probed in detail by thermogravimetry (TG), Rietveld refinement, and solid-state nuclear magnetic resonance (ss-NMR) analyses. The strength and acid density were systematically investigated by exploring the host-guest interactions between the probed molecule CD₃CN and the framework using ¹H magic angle spinning (MAS) NMR spectroscopy, and the local environments of Si were studied by ²⁹Si MAS NMR spectroscopy. The results of TG and Rietveld refinement showed that the SAPO-34 MSs templated by TEAOH and DIPA have only one OSDA per cha (one of the composite building units) cage in the longitudinal configuration, while those templated by nBA and MOR possess two OSDAs occluded in the cha cage in an up-and-down arrangement. Interestingly, the acid strength of SAPO-34 templated by TEAOH increased with increasing Si content, while the acid density remained almost unchanged. In contrast, the acid density of SAPO-34 templated by DIPA decreased evidently with an increase in the Si content, while the acid strength showed only a small variation. Among the other two samples, SAPO-34 templated by MOR has the most amounts of acid densities compared to SAPO-34 templated by nBA, while the strength is not superior. Thus, we conclude that the acid density is associated with the number of OSDAs in each cha cage and their protonation ability, while the difference in acid strength is attributed to the number of Si atoms at the edges of the Si islands. The findings of this study will provide insight into the acid properties of related crystalline porous materials.

The intercalation of potassium in graphite provides high energy density owing to the low potential of 0.24 V vs. K/K⁺, thereby making it a promising anode material for potassium ion batteries. However, the high volume expansion (60%) of graphite after potassium intercalation induces significant stress and electrode pulverization. Additionally, the sluggish kinetics of potassium insertion undermine the rate capability of electrodes. Using few-layer exfoliated graphite (EG) as a negative electrode material effectively relieves expansion-induced stress. Unfortunately, the close stacking of ultra-thin two-dimensional EG impedes ion transport. Furthermore, EG with smooth surfaces lacks active sites to adsorb K⁺, which is unfavorable for intercalation reactions. To address these problems, in this study, we designed an rGO/EG/rGO sandwich that coats EG with reduced graphene oxide (rGO). This complex material has two main advantages: (1) its 3D network can effectively prevent EG from stacking and buffer the volumetric variation of EG to improve the cyclic stability of the electrode, and (2) the loose structure and rich functional groups of rGO can also enhance the kinetic of potassium intercalation. Through hydrothermal reduction, GO was coated onto the EG surface and cross-linked to form a 3D network, by which EG stacking could be effectively mitigated. The rGO : EG ratio was precisely controlled by modulating the amount of reactant GO and EG. Transmission electron microscopy and scanning electron microscopy images showed that the rGO was uniformly coated on the EG surface to form a sandwich structure. X-ray diffraction patterns and Raman spectra demonstrated that rGO was physically adsorbed on the EG surface without notable chemical interactions. The EG structure was retained to ensure that its characteristic electrochemical properties were unaffected. Cyclic voltammetry and galvanostatic cycling tests were performed on the complex material with various rGO : EG ratios, exhibiting that rGO : EG = 1 : 1 (w/w) was optimal with a specific capacity of 443 mAh·g^-1 at 50 mA·g^-1. Even when operated at a high current density of 800 mA·g^-1, a specific capacity of 190 mAh·g^-1 was achieved, retaining 42.9% of the low-rate capacity, far exceeding those of pristine EG (14.2%) and rGO (27.2%). These results demonstrate that the rGO coating indeed enhanced the kinetics of potassium intercalation and efficiently improved the capacity and rate capability compared to pristine EG. We hope this work sheds light on novel approaches to improving potassium intercalation mechanisms in graphite.

Since the First Industrial Revolution, traditional fossil energy (coal, petroleum, etc.) has been the most important energy source. However, with social progress and technological development, energy consumption continues to increase. But fossil energy not only has limited reserves, it also causes serious problems (environmental pollution, the greenhouse effect). Therefore, the research and development of clean and sustainable energy are particularly important. One research focus is hydrogen energy. Hydrogen is a promising energy carrier due to its high energy density, clean-burning characteristics, and sustainability. However, the challenges of hydrogen storage and transportation seriously limit its practical application in proton exchange membrane fuel cells. A potential solution is hydrogen storage in the form of a more stable precursor. One such precursor, formic acid, decomposes easily at room temperature in the presence of a catalyst without also producing toxic gases. Effective catalysts for formic acid decomposition (FAD) are key to hydrogen production by this method. In this study, a high-performance palladium (Pd)-based catalyst boosted by thin-layered carbon nitride was prepared for formic acid decomposition. First, trimeric thiocyanate was calcined by a one-step method to obtain carbon nitride (C₃N₄-S) directly, followed by fabrication of a Pd-based FAD catalyst with C₃N₄-S as support (Pd/C₃N₄-S). During the pyrolysis of thiocyanuric acid, the overflow of -SH in the precursor had a peeling effect, so that the C₃N₄ formed as a thin, broken layer with a large specific surface area and pore volume. Because of the improved specific surface area and pore volume and the resulting large number of defect attachment sites, the C₃N₄-S support effectively dispersed Pd nanoparticles. Furthermore, owing to the electron effect between the support and the metal, the Pd²⁺ content on the catalyst surface could be adjusted effectively. Pd/C₃N₄-S showed excellent FAD performance. This catalyst decomposed formic acid into CO₂ and H₂ effectively at 30 ℃. The turnover frequency and mass activity were as high as 2083 h^-1 and 19.52 mol·g^-1·h^-1, respectively. Testing of the gas product by gas chromatography showed that it did not contain CO, indicating that the Pd/C₃N₄-S catalyst had excellent selectivity. The catalyst also had good stability: its performance decreased by less than 10% after four testing cycles. This study provides a guiding example of development of a formic acid hydrogen production catalyst with high cost performance and a simple preparation method.

Carbon dots (CDs), as a kind of carbon-based fluorescent nanodots (FNDs), not only retain the advantageous characteristics of carbon-based materials (e.g., low toxicity and biocompatibility) but also exhibit tunable fluorescence emission, low photobleaching, and undergo facile surface functionalization. Therefore, the prospect of applying these materials for analysis and detection, cell imaging, drug delivery, light-emitting devices, photocatalysis, biosensing, and cancer treatment is promising. Although the synthesis of carbon dots from green and renewable feedstocks as biomass carbon sources is possible, the controllability of the involved chemical reactions is poor, resulting in poor atom economy, low quantum yields, and, especially, extremely low yields of carbon dots. In addition, these disadvantages could lead to an increase in equipment requirements and could pose a safety risk because of the need for hydrothermal and solvothermal synthesis. Certain methods even require large amounts of acid/alkali, strong oxidants, or organic solvents, thereby complicating the post-processing process and generating waste and emissions. This research aimed to implement a new idea, namely to "fabricate" rather than "synthesize" carbon-based FNDs from a certain kind of natural and small unsaturated molecule with surface activity relying on a self-assembling and self-crosslinking strategy in lieu of traditional approaches that involve uncontrollable reactions with unknown mechanisms including pyrolysis, dehydrolysis, polyconcensation, and carbonization. In this context, conjugated linoleic acid (CLA) has been studied extensively in our laboratory, and was found to have the self-assembly and self-crosslink characteristics required by the above innovative strategy. This motivated us to adopt CLA as a new carbon source in this study. First, CLA self-assembles into unsaturated fatty acid liposomes (ufasomes) in an aqueous solution of pH 8.6 at ambient temperature (15-25 ℃), and then, the initiator Ammonium persulfate is added to induce self-crosslinking of the ufasomes at 80 ℃ to obtain firm and uniform nanoparticles. On this basis, the possibility of using them as FNDs is investigated. Consequently, FNDs based on self-crosslinked ufasomes (SCU-FNDs) are prepared in high FND yield of 73.9% after dialysis, with a consistent particle size (17 nm), a degree of self-crosslink (DSC) of 75%, and emission of bluish green fluorescence excited at 320 nm. Furthermore the "fabrication" route provided a clear solution of FNDs that could be applied directly without separation and purification and with no wasteful emissions, which is therefore beneficial for large-scale preparation. The experimental results showed that the fluorescence intensities of the SCU-FNDs are positively correlated with both the surface carboxyl groups and DSC results. A reasonable explanation for the former relationship is the effect of the restricted geometry of the ufasomes on the accumulation of oxygen atoms at the surface of FNDs, whereas the latter could be explained by the confinement effect of the covalent crosslink on the motion of the hydrocarbon chain of the CLA molecules. The experimental results also showed that the SCU-FNDs have temperature-sensitive fluorescence properties, which is attributed to the motion of the residual hydrocarbon chain inside the SCU-FNDs even though they have been locally polymerized. The change in the fluorescence intensity of the FNDs as a function of the temperature was good in accordance with the linear relationship I/I₀ = -0.00922T + 1.229 (R² = 0.99) in the range of 25-85 ℃, which demonstrates the potential for preparing green and safe undoped FNDs for use as biocompatible and temperature-sensitive fluorescent probes.

The design functions of lithium-ion batteries are tailored to meet the needs of specific applications. It is crucial to obtain an in-depth understanding of the design, preparation/ modification, and characterization of the separator because structural modifications of the separator can effectively modulate the ion diffusion and dendrite growth, thereby optimizing the electrochemical performance and high safety of the battery. Moreover, the development and utilization of various characterization techniques are critical and essential in bridging the intrinsic properties of separators and their impacts on the electrochemical performance, which guide the functional modification of the separators. In this review, we systematically summarized the recent progress in the separator modification approaches, primarily focusing on its effects on the batteries' electrochemical performance and the related characterization techniques. Herein, we provide a brief introduction on the separators' classification that mainly includes (modified) microporous membranes, nonwoven mats, and composite membranes; thereafter, we discuss the basic requirements that facilitate the use of membranes as separators, such as good wettability with electrolyte, high permeability for ions, and several intrinsic properties including good thermal stability, electronic insulation, excellent (electro)chemical stability, high mechanical strength, and appropriate thickness/porosity. We then highlight the factors that affect the batteries' performance from the viewpoints of ion diffusion, dendrite growth, and safety, along with the modification approaches. Specifically, the separator should possess high ionic conductivity and uniform ion transmission, which can be achieved by adjusting its composition and through surface modifications. The severe dendrite growth, especially in lithium-metal batteries, could be inhibited by controlling the pore structures, increasing affinity between separator and metal anode, constructing artificial solid electrolyte interphase (SEI), adopting high strength separator, as well as smart design of the separator. The safety issue, which is a major concern that limits battery applications, could be mitigated by increasing the separator's mechanical strength, thermal stability, and shutting the batteries down below thermal runaway temperature through various functionalization approaches. More importantly, the characterizations of the separators' structure, and their mechanical, thermal, and electrochemical properties are systematically summarized, including scanning electron microscope (SEM)/atomic force microscope (AFM) for surface morphology observation, focused ion beam scanning electron microscopic (FIB-SEM)/X-ray tomography (X-ray CT) for 3D structure detection, mercury intrusion porosimetry (MIP)/Brunauer-Emmett-Teller (BET)/Gurley number measurement for pore structure analysis, contact angle and climbing behavior of electrolyte in separators for wettability measurements, characterizations of the separator's tensile behavior, puncture behavior and compression behavior, thermo-gravimetric analysis (TGA)/differential scanning calorimetry (DSC)/infrared thermography (FLIR) for thermal properties test, and the electrochemical methods for determining the separator's electrochemical stability, ionic conductivity, internal resistance, lithium-ion transference number, cycle/rate performance, as well as self-discharge characteristic. These characterizations provide theoretical and practical basis for the rational design of functional separators and optimization of the electrochemical performance of lithium-ion batteries. Finally, we provide the perspectives on several related issues that need to be further explored in this research field.

The gradual popularization of new energy technologies has led to rapid development in the field of electric transportation. At present, the demand for high-power density batteries is increasing and next-generation higher-energy battery chemistries aimed at replacing current lithium-ion batteries are emerging. The lithium-air batteries (LABs) are thought to be the ultimate energy conversion and storage system, because of their highest theoretical specific energy compared with other known battery systems. Current LABs are operated with pure O₂ provided by weighty O₂ cylinders instead of the breathing air, and this configuration would greatly undermine LAB's energy density and practicality. However, when the breathing air is used as O₂ feed for LABs, CO₂, as an inevitable impurity therein, usually leads to severe parasitic reactions and can easily deteriorate the performance of LABs. Specifically, Li₂O₂ will react with CO₂ to form Li₂CO₃ on the cathode surface. Compared with the desired discharge product Li₂O₂, the Li₂CO₃ is an insulating solid, which will accumulate and finally passivate the electrode surface leading to the "sudden death" phenomenon of LABs. Moreover, Li₂CO₃ is hard to decompose and a high overpotential is required to charge LABs containing Li₂CO₃ compounds, which not only degrades energy efficiency but also decomposes other battery components (e.g., cathode materials and electrolytes). In recent years, researchers have proposed many strategies to alleviate the negative effects brought about by Li₂CO₃, such as catalyst engineering, electrolyte design, and so on, in which O₂ selective permeable membranes are worth noting. This review summarizes the recent progresses on the understanding of the CO₂-related chemistry and electrochemistry in LABs and describes the various strategies to mitigate and even avoid the negative effects of CO₂. The perspective of CO₂ separation technology using selective permeable membranes/filters in the context of LABs is also discussed.

Supercapacitors that can withstand extremely low temperatures have become desirable in applications including portable electronic devices, hybrid electric vehicles, and renewable energy conversion systems. Graphene is considered as a promising electrode material for supercapacitors owing to its high specific surface area (up to 2675 m²·g^-1) and electrical conductivity (approximately 2 × 10² S·m^-1). However, the restacking of graphene sheets decreases the accessible surface area, reduces the ion diffusion rate and prolongs the ion transport pathways, thereby limiting the energy storage performance at low temperatures (typically < 100 F·g^-1 at sub-zero temperatures). Herein, we fabricate a supercapacitor based on holey graphene and mixed-solvent organic electrolyte for ultra-low-temperature applications (e.g., -60 ℃). Reduced holey graphene oxide (rHGO) was synthesized as the electrode material via an oxidative-etching process with H₂O₂. Methyl formate was mixed with propylene carbonate to improve the electrolyte conductivity at temperatures ranging from -60 to 25 ℃. The as-fabricated supercapacitor showed a high room-temperature capacitance of 150.5 F·g^-1 at 1 A·g^-1, which was almost 1.5 times greater than that of the supercapacitor using untreated reduced graphene oxide (rGO; 101.4 F·g^-1). The improved capacitance could be attributed to the increased accessible surface rendered by the abundant mesopores and macropores on the holey surface. As the temperature decreased to -60 ℃, the rHGO supercapacitor still delivered a high capacitance of 106.2 F·g^-1 with a retention of 70.6%, which was superior to other state-of-the-art graphene-based supercapacitors. Electrochemical impedance spectra tests revealed that the ion diffusion resistance in rHGO was significantly smaller than that in rGO and less influenced by temperature with a lower activation energy. This was because the holey morphology can provide transport pathways for ions and reduce the ion diffusion length during charging/discharging, consequently diminishing the diffusion resistance at low temperatures. Specifically, at -60 ℃, the energy density of supercapacitor reached up to 26.9 Wh·kg^-1 at 1 A·g^-1 with a maximum power density of 18.7 kW·kg^-1 at 20 A·g^-1, surpassing the low-temperature performance of conventional carbon-based supercapacitors. Moreover, after 10000 cycles at -60 ℃ with a current density of 5 A·g^-1, 89.1% of capacitance was retained, suggesting the stable and reliable power output of the current supercapacitor at extremely low temperatures.

Metal-organic nanostructures on surfaces have attracted considerable attention owing to their structural stability and potential applications. In metal-organic nanostructures, metal atoms are derived from the externally deposited metals or native surface atoms. Externally deposited metals are of rich diversity and depend on the targeted nanostructures. However, native surface atoms are restricted to single-crystalline metal surfaces of gold, silver, and copper, which are usually used in surface science. Metal-organic nanostructures mostly consist of Au- or Cu-coordinated motifs, while only a few consist of surface Ag atoms. Further investigation into the molecule-metal interactions is beneficial for the accurately controlled fabrication of the desired nanostructure. As for the building blocks, organic molecules coordinate with native surface atoms by M―C, M―N, and M―O bonds. The reactions of terminal alkynes or Ullmann couplings could realize the formation of C―M―C linkages. Cu and Au atoms could coordinate with molecules with terminal cyano or pyridyl groups to form N―M―N bonds. In addition, surface Ag adatoms could coordinate with phthalocyanine through Ag―N bonds. However, a comprehensive study of M―O coordination bonds is still lacking. Thus, we used hydroxyl-terminated molecules to coordinate with Ag adatoms to form metal-organic coordination nanostructures and study the O―Ag linkages. In this case, we successfully built and investigated a series of ordered structures by depositing 4, 4'-dihydroxy-1, 1': 3', 1''-terphenyl (H3PH) molecules on the Ag(111) surface by scanning tunneling microscopy. At room temperature, a close-packed ordered structure was formed by H3PH molecules through cyclic hydrogen bonds, and the repeat unit of such nanostructures contained eight H3PH molecules. Upon increasing the annealing temperature, the formation of O―Ag bond led to a change in the self-assembly pattern. When the annealing temperature was increased to 330 K, a new ordered nanostructure occurred due to the combination of O―Ag coordination and hydrogen bonds. Upon further increasing the annealing temperature to 420 K, a honeycomb structure and coexisting two-fold coordination chains appeared, which only consisted of O―Ag―O linkages. Density functional theory calculations were carried out to analyze the metal-molecule reaction pathways and energy barriers of the O―Ag―O bonds. The energy barrier of the O―Ag bond is 1.41 eV, which is less than that of the O―Ag―O linkage calculated to be 1.85 eV. The low energy barrier of the O―Ag bond and large coordination energy of the O―Ag―O linkage can be attributed to the formation of the hierarchical metal-organic nanostructure. The results obtained herein provide an effective approach for designing and building two-dimensional hierarchical structures with organic small molecules and metal adatoms on single-crystalline metal surfaces.

The electrocatalytic carbon dioxide reduction reaction (E-CO₂RR) has attracted attention in recent years for its ability to effectively alleviate the environmental problems caused by the rapid increase of CO₂ in the atmosphere and transform CO₂ into high value-added fuels or chemicals (e.g., CO, HCOOH, CH₄, CH₃OH, C₂H₄, C₂H₅OH, etc.) under mild conditions. In addition, clean energy sources, such as solar and wind energy, can provide electrical energy for the electrochemical CO₂ conversion technology used in large-scale industrial applications. One limitation of the E-CO₂RR is that CO₂ is a thermodynamically stable linear molecule with a slow kinetic reaction rate. In addition, the E-CO₂RR involves complex processes, such as gas diffusion and multi-electron transfer, making its selectivity problematic. Therefore, constructing highly efficient and stable catalytic electrodes has become a core research topic in the field of E-CO₂RR. Unfortunately, the traditional method of coating electrodes with binders (e.g., Nafion, polyvinylidene fluoride, and polytetrafluoroethylene) usually results in a low utilization ratio of active sites due to the easy aggregation of the catalysts themselves. This could result in the severe embedding of active sites and limited mass transfer. Moreover, the dissolution of the catalyst layer during the electrocatalytic process also reduces the activity and stability of the electrodes, making it difficult to reuse. Therefore, it is necessary to regulate the electrode reaction interface to improve the utilization ratio of active sites. The integrated electrodes, where the catalyst is grown directly on the current collector, can avoid the use of binders to facilitate the exposure of active sites and transfer of electrons. The integrated structure can also enhance the bonding strength between the active material and current collector and improve the cycling stability of the electrodes. Meanwhile, the micro-environment (e.g., pH, concentration of CO₂, and intermediates) at the three-phase interface can be effectively controlled on the integrated electrodes, which can enhance the performance of the E-CO₂RR. In recent years, encouraging progress has been achieved in the study of the E-CO₂RR. However, current reviews of the E-CO₂RR mainly focus on the regulation of the intrinsic activity of catalysts; discussions and reviews from the perspective of the electrodes are rarely reported. This article reviews the latest research of the integrated electrodes for the E-CO₂RR with a focus on the application of different types of integrated electrodes (e.g., metal, alloy, metal oxide, metal sulfide/phosphide, and metal single atom). It also analyzes the effects of morphology, surface, and interface regulation on the electrocatalytic performance of the E-CO₂RR. Finally, it highlights the challenges that still exist in this field and discusses the future development of the integrated electrodes.

A unique mixed-dimensional van der Waals heterostructure can be formed by integrating one-dimensional (1D) and two-dimensional (2D) materials. Such a 1D/2D mixed-dimensional heterostructure will not only inherit the unique properties of 2D/2D heterostructures, but also has a variety of stacking configurations, offering a new platform to adjust its structure and properties. The combination of p-type 1D single-walled carbon nanotubes (SWCNTs) and n-type 2D molybdenum disulfide (MoS₂) is one such example, possessing tunable properties. In situ chemical vapor deposition (CVD) is one of the most effective methods to construct 1D SWCNT/2D MoS₂ mixed-dimensional heterostructures. There are several reports of successfully grown SWCNT/MoS₂ heterostructures. The reports indicate that these heterostructures exhibit strong electrical and mechanical couplings between the SWCNTs and MoS₂, making it suitable for the construction of high-performance electronic and optoelectronic devices. However, there are still several problems associated with the in situ CVD growth of SWCNT/MoS₂ heterostructures. First, the growth mechanism of the 1D SWCNT/2D MoS₂ heterostructure is unclear. We still do not know how the existence of small-diameter SWCNTs will affect the nucleation and growth process of MoS₂. It is undetermined whether MoS₂ flakes will grow above the preexisting SWCNTs or under them. Second, current studies all report the growth of MoS₂ on a substrate sparsely covered by SWCNTs, which have a wide chirality distribution. Since the chirality of SWCNTs determines their physical properties and the density of SWCNTs significantly affects its performance in electronic devices, both the low density and wide chirality distribution of SWCNTs reported in these studies impose negative impacts on the interface behavior of SWCNT/MoS₂ heterostructures and their performance in devices. Herein, we report the preparation of high-quality 1D SWCNT/2D MoS₂ heterostructures by directly growing MoS₂ on dense and narrow-chirality distributed SWCNTs on a silicon substrate. To achieve this goal, high-purity semiconducting SWCNTs with narrow chirality distributions were sorted from the raw arc-discharged SWCNTs, and then high-density SWCNT arrays or networks were formed on a silicon substrate by dip-coating. Through in-depth analyses of the surface morphology and structure of the nuclei, we found that MoS₂ may prefer to grow under the SWCNTs and will grow much faster in the grooves between the SWCNTs to form a growth front. Therefore, an interesting "absorption-diffusion-absorption" growth mechanism has been proposed to explain the nucleation and growth process of SWCNT/MoS₂ heterostructures. In addition, we confirm the presence of strong charge coupling in the mixed-dimensional heterostructure through Raman analysis. Carriers can be quickly transferred through the interface between the SWCNTs and MoS₂, paving a way for the future design and fabrication of novel electronic and optoelectronic devices based on 1D/2D heterostructures.

Photocatalytic hydrogen evolution is a scalable pathway to generate hydrogen fuels while mitigating environmental crisis. Strategies based on modification of the host photocatalyst surface are key to improve the adsorption/activation ability of the reaction molecules and the efficiency of charge transport, so that high-efficiency photocatalytic systems can be realized. Cadmium sulfide (CdS), a visible light-responsive semiconductor material, is widely used in photocatalysis because of its simple synthesis, low cost, abundant raw materials, and appropriate bandgap structure. Many researchers have focused on improving the photocatalytic efficiency of CdS because the rapid charge recombination in this material limits its applications. Among the various strategies proposed in this regard, surface modification is an effective and simple method used to improve the photocatalytic performance of materials. In this work, polyvinyl pyrrolidone (PVP)-capped CdS (denoted as P-CdS) nanopopcorns with hexagonal wurtzite (WZ)-cubic zinc blende (ZB) homojunctions were fabricated via one-step gamma-ray radiation-induced reduction under ambient conditions. Subsequent alkaline treatment under ambient conditions led to a dramatic improvement in the activity of the alkalized PVP-capped CdS (MP-CdS) photocatalyst. The structure and properties of the photocatalyst were determined by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) analysis, Brunauer-Emmett-Teller (BET) specific surface area measurements, and photoelectric tests. The photocatalytic performance was evaluated based on the photocatalytic H₂ evolution under visible-light irradiation. The mechanism underlying the enhancement of the photocatalytic activity is also discussed. The results showed that after the alkaline treatment, the crystal structure of CdS with WZ-ZB homojunctions was preserved, but PVP on the surface of CdS hydrolyzed to form PVP hydrolysis product (MPVP) with carboxyl and amino groups. Owing to the increased alkaline solubility, a portion of MPVP dissolved into the solution and was removed from the surface of MP-CdS, exposing a greater number of active sites of the WZ-ZB phase junctions with a larger specific surface area. On the other hand, the carboxyl groups in MPVP coordinated with CdS could affect the bandgap and valence band position of CdS to facilitate the photocatalysis. Because of the synergistic effects of the exposure of WZ-ZB phase junctions and band structure engineering, the alkalized samples at a 1 mol·L^-1 concentration of NaOH showed a H₂ evolution rate of 477 μmol·g^-1·h^-1 under visible-light illumination, which was twice that obtained for the pristine P-CdS photocatalysts. This simple and low-cost post-synthesis strategy can be extended to the preparation of diverse functional photocatalysts. The present work is expected to contribute to the practical application of sulfide photocatalysts.

Fibers and textiles with good flexibility, air permeability, and mechanical properties are indispensable materials in our daily lives. With the rapid development of flexible electronics, fabricating fibers and textiles that exhibit intelligent characteristics has become an attractive research topic. On the basis of the characteristics of common fibers or textiles, intelligent fibers and textiles may exhibit unique functions such as sensing, feedback, response, self-diagnosis, self-repair, and self-regulation. The development of intelligent fibers and textiles is closely related with the development of material science. Many materials, including metals, artificial polymers and natural biopolymers can be used for fabricating intelligent fibers and textiles. Compared with metals and artificial polymers, natural biopolymers have advantages of green source, biosafety, biodegradability and lightweight. Among natural biopolymers, natural silks, especially that from Bombyx mori, can be obtained in large amounts and have been used for clothes for thousands of years. Silkworm silk has exceptional mechanical properties, attractive luster, good biocompatibility and biodegradability. Therefore, silk materials are considered to be one of most promising candidates for intelligent fibers and textiles. In this review, we firstly introduce the hierarchical structures and basic properties of natural silk fibers. The exceptional mechanical properties of silk fibers can be ascribed to their unique hierarchical structures (from polypeptide chains, secondary structures to macroscopic fibers). The approaches to fabricate regenerated silk materials are briefly reviewed. The basic properties of silk materials, including the mechanical properties, biocompatibility, biodegradability, optical properties, piezoelectric properties, and thermal stability are presented. Then, the application of silk materials in various intelligent fibers and textiles, including fiber-based sensors, actuators, optical devices, energy harvesting and storage devices, are reviewed. Silk fibers can be functionalized and made into strain sensors, pressure sensors, and humidity sensors for applications in health monitoring. They can also transform into electrically conductive materials through high-temperature carbonization and then be fabricated into high-performance sensors or other functional devices. Silk-based actuators have been fabricated based on the response of silk to water or other molecules. Besides, silk-based fluorescence fibers and optical fibers were developed. Silk fibers have also been used in wearable energy devices by designing and fabricating piezoelectric nanogenerators, triboelectric nanogenerators, super-capacitors and batteries. The preparation methods, performance, and working mechanisms of those silk-based intelligent fibers and textiles are discussed in details. Finally, the persisting challenges and future opportunities of silk-based intelligent fibers and textiles are discussed. We believe that silk-based materials have great potential for intelligent fibers and textiles. The further development of this field will be accelerated by the continued development of material science and related techniques.

Graphene oxide (GO) possesses a large number of oxygen-containing functional groups on its basal planes and edges, enabling it to disperse well in water and other aqueous media. This property facilitates the processing of GO by various wet-processing methods. Because of its interesting properties and useful intermediate role in preparing graphene derivatives, GO has potential applications in many fields, including composites, separators, sensors, actuators, and energy storage and conversion. At high concentrations, strong, competitive interactions occur in GO aqueous dispersions that significantly impact the rheological behavior of these dispersions. In a liquid medium, the dispersed GO nanosheets form a unique colloidal system, in which solvation, electrostatic interactions, hydrogen bonding, and the lyophilic effect play important roles. The aromatic domains preserved from precursor graphite show attractive van der Waals interaction and π–π stacking between GO sheets. In this study, the effects of pH, temperature, and different organic solvents on the rheological behavior of GO dispersions were investigated through steady and dynamic rheological tests and theoretical analysis. The results showed that enhancing acidity, increasing the temperature within a certain range, and adding organic solvents such as pyridine promote transition of the GO aqueous dispersion from a viscoelastic liquid to a gel state, which shows different rheological properties. GO sheets in dispersion interact through negative charges originating from the many ionizable groups in the nanosheets and electrical double layers. Analysis using the Deryagin-Landau-Verwey-Overbeek (DLVO) theory showed that, under the conditions described above, these interactions were remarkably altered with consequent effects on the rheological properties. Weakened electric double-layer interaction disrupted the GO colloidal dispersion state and resulted in the association of GO nanosheets to form gel. Based on the above understanding, the yield stress of the GO dispersions affected by the volume fraction was analyzed by population balance equation (PBE) modeling. Through creep and relaxation experiments, the structure and rheological properties of GO dispersions at high concentrations were found to be similar in many respects to those of polymers. Therefore, the viscoelastic behavior of GO dispersions can be well described by the Poynting-Thomson model, which can provide theoretical support and advance the study of complex GO dispersions. These results shed new light on the rheological behavior of GO dispersions and can be used to optimize the processing conditions for future applications.

Polymer films are widely used as biomaterials, electronic devices, food packaging materials and gas separation membranes. In practice, cross-linking is an effective method to enhance their stability and increase the strength of these films. However, conventional cross-linked polymer films cannot degrade under mild conditions. Herein, we fabricated two cross-linkable, yet biodegradable, polymer films of ~0.2 mm via solution casting using cinnamate-grafted polycaprolactones, namely: a poly((α-(cinnamoyloxymethyl)-1, 2, 3-triazol) caprolactone) (PCTCL₁₃₃) homopolymer and a poly(caprolactone-stat-CTCL) (P(CL₁₅₆-stat-CTCL₂₈)) copolymer. The successful syntheses of the polymers were confirmed via proton nuclear magnetic resonance (¹H NMR) spectroscopy, size exclusion chromatography (SEC), and Fourier transform infrared (FT-IR) spectroscopy. The PCTCL homopolymer appeared as a transparent film, owing to its side groups that impede its crystallinity; in contrast, the copolymer film appeared translucent, owing to its PCL segments that are easily crystallized. The cinnamate groups facilitated the cross-linking of the polymer films when irradiated by ultraviolet (UV) light; this is indicated by its insoluble character in tetrahydrofuran, which is a good solvent for both polymers. SEC analysis indicated that a fraction of the P(CL₁₅₆-stat-CTCL₂₈) film remained un-cross-linked after irradiation, owing to its crystalline structure. In contrast, UV irradiation caused the PCTCL homopolymer film to become homogeneously cross-linked, which exhibited a cross-linking density of 49% after 2 h as indicated by the ¹H NMR results. Thermogravimetric analysis (TGA) indicated that cross-linking of the PCTCL films caused a minimal change in thermal stability. Both the cross-linked polymer films were able to degrade upon the addition of a modest amount of concentrated hydrochloric acid, as confirmed by SEC and ¹H NMR. However, the degradation rate significantly decreased after cross-linking, thereby indicating its tunable character that can be altered by varying the cross-linking density. In addition, the rate of degradation can be adjusted upon varying the fraction of cross-linked PCTCL groups in the copolymer. In principle, treating the polymer films with sufficient amounts of acid could form degradation products with molecular weights less than 300 g∙mol⁻¹. To further explore the mechanical properties of such materials, we investigated the correlation between the initial concentration used for solution casting and the Young's modulus of the film by employing molecular dynamics simulations. These results indicate that tougher films are prepared when using more concentrated polymer solutions, owing to a higher degree of chain entanglement. In summary, the prepared films with tunable degradability are promising materials for biomedical applications. In principle, this platform could be utilized in hydrogels and coating materials for a broad scope of applications.

Solid oxide fuel cell (SOFC) with high energy conversion efficiency, low pollutant emission, and good fuel adaptability has witnessed rapid development in recent years. However, the commercialization of SOFC remains limited by constraints of performance and stability. Electrochemical impedance spectroscopy (EIS) can distinguish ohmic impedance caused by ion transport from polarization impedance related to electrode reaction; it has been widely used in the research of performance and stability as an efficient on-line characterization technology. The physical/chemical processes involved in EIS overlap significantly and can be decomposed by the distribution of relaxation times (DRT) method which does not depend on prior assumptions. Since industrial large-size SOFC is vulnerable to the influence of inductance and disturbance when testing EIS, its EIS analysis is rarely studied and mostly based on the research results of cells with smaller electrode active area. To further elucidate the impedance spectrum of industrial large-size SOFC under actual working conditions, the EIS of industrial-size (10 cm × 10 cm) anode-supported planar SOFC was systematically tested over a broad temperature and anode/cathode gas composition range. First, the quality of the impedance data was examined by performing a Kramers-Kronig test. The residuals of real and imaginary data were within the range of ±1%, indicating good data quality. Then, the DRT method was adopted to parse the EIS data. By comparing and analyzing the DRT results under different conditions, the corresponding relationships between each characteristic peak in the DRT results and the specific electrode process in the SOFC were revealed. The characteristic frequencies were separated into 0.5-1, 1-30, 10-30, 1 × 10²-1 × 10³, and 1 × 10⁴-3 × 10⁴ Hz regions, corresponding to gas conversion within the anode, gas diffusion within the anode, oxygen surface exchange reaction within the cathode, charge-transfer reaction within the anode, and oxygen ionic transport process, respectively. In this study, the identification of each electrode process in industrial large-size SOFC is realized, indicate that the gas conversion process in large-size SOFC with larger active area and smaller flows cannot be ignored compared with the cells with smaller electrode active area. The method followed and the results obtained have a universal quality and can be applied to the in situ characterization, online monitoring, and degradation mechanism research of SOFC, thus laying a foundation for the optimization of the performance and stability.

Pt-based catalysts are widely used in diesel oxidation catalyst (DOC) units, primarily to oxidize the harmful HC, CO, and NO emissions. Notably, NO₂ produced from NO oxidation is beneficial for low-temperature activity in NH₃-SCR and promotes soot oxidation in diesel particulate filters (DPF). Thus, the conversion of NO is an important parameter for determining the performance of DOCs. Considering the increasingly stringent emission regulations and the economic effectiveness, preparation of low-cost and highly active Pt-based catalysts is indispensable. Generally, the Pt⁰ content is crucial as it is an active component of DOCs. Small Pt size is beneficial for improving the catalytic activity. In this study, we applied a modified alcohol reduction-impregnation (MARI) method to synthesize highly active 1% (w, mass fraction) Pt/SiO₂-Al₂O₃ (denoted as MA-Pt/SA) catalyst. Meanwhile, using the conventional impregnation method, we prepared the Pt/SiO₂-Al₂O₃ catalyst with the same Pt loading (denoted as C-Pt/SA) as a reference sample. X-ray photoelectron spectroscopy (XPS) and hydrogen temperature program reduction (H₂-TPR) analyses proved that the MARI method could produce Pt catalysts with higher Pt⁰ content. Pt⁰ content in MA-Pt/SA was ~60.3% while that in C-Pt/SA was only ~23.1%. X-ray diffraction (XRD), CO-diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS), and transmission electron microscopy (TEM) characterization confirmed that the Pt particle size is much smaller over MA-Pt/SA as compared to that over C-Pt/SA. Performance evaluation of MA-Pt/SA and C-Pt/SA was conducted in a simulated diesel atmosphere. The results showed that the maximum NO conversion into NO₂ over MA-Pt/SA is 74% and 68% in the absence and presence of H₂O, respectively, which were much higher than those over C-Pt/SA (42% and 51% NO conversion with and without H₂O, respectively). Furthermore, the temperature for 30% NO conversion over MA-Pt/SA (218 ℃) markedly decreased as compared to that over C-Pt/SA (248 ℃), indicating the excellent low temperature activity. After the aging treatment with reaction gas at high temperatures, aged MA-Pt/SA maintained 69% NO conversion while aged C-Pt/SA showed only 41% NO conversion. In addition, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NO + O₂ co-adsorption suggested that higher Pt dispersion and higher Pt⁰ content over MA-Pt/SA could facilitate the formation of bridging nitrates as intermediate species in NO oxidation at lower temperatures and could also facilitate their rapid decomposition (or desorption) at higher temperatures, thus imparting a high catalytic activity. Furthermore, a decrease in the Pt loading to 0.5% (w) resulted in a maximum NO conversion of 64% via the MARI method, suggesting a higher catalytic activity compared to that of C-Pt/SA with 1% (w) Pt loading. This work provides a method to prepare highly active Pt-based catalysts with low noble loading.

Electroreduction of CO₂ is one of the most promising CO₂ conversion pathways because of its moderate reaction conditions, controllable product composition, and environment-friendliness. However, most of the current CO₂ electroreduction technologies have not reached the techno-economic threshold for a competitively profitable electrochemical process. Based on a simple two-electron transfer process, the electroreduction of CO₂ to CO, which is further processed into syngas with the reduction of H₂O to H₂, is postulated to be the most promising pathway for a profitable electrochemical process. Such a process urgently requires nonprecious electrocatalysts that can precisely control the CO/H₂ ratio. Herein, we present a tailored synthesis of bifunctional electrocatalysts with high activity, which can realize the preparation of syngas with controlled compositions via molecular engineering of a ternary nanocomposite. Specifically, a mixture of melamine, triphenylphosphine, and nickel acetate was milled and dissolved in ethanol; the ternary nanocomposite was obtained after rotary evaporation of the mixture. We prepared the catalysts by pyrolyzing the obtained composites at 850 ℃ for 2 h. The synthesis strategy was facile and easy to scale. The specific surface area and pore volume of the bifunctional electrocatalyst were both significantly enhanced upon increasing the concentration of the phosphorus source, triphenylphosphine, during the precursor preparation. The obtained bifunctional electrocatalysts had hierarchically porous structures, which had well-dispersed active sites and could promote mass transport. Raman spectra revealed higher degrees of disorder with higher P/Ni ratios in the precursor. X-ray photoelectron spectroscopy verified the presence of Ni-P_x and Ni-N_x functionalities, which were the active sites for hydrogen evolution and CO₂ reduction, respectively. Hence, the electrocatalytic performance of this series of bifunctional electrocatalysts can be tuned from CO-dominant to H₂-dominant. The electrochemical performance was evaluated using a CO₂-saturated 0.5 mol·L^-1 KHCO₃ aqueous solution at ambient temperature by linear sweep voltammetry and potentiostatic electrolysis. Through these experiments, we determined that the activity of the catalysts was influenced by the surface phosphorus/Ni-N_x site ratio. The highest CO faradaic efficiency (91%) was achieved at -0.8 V (vs a reversible hydrogen electrode, RHE) with Ni-N-C in the absence of Ni-P. The CO/H₂ molar ratio in the syngas stream was tunable from 2 : 5 to 10 : 1 in the potential range from -0.7 to -1.1 V (vs RHE) with a total faradic efficiency of 100%. The syngas composition directly links to the molar ratio of the two integrated components, nickel phosphide and Ni-N-C. Additionally, the stability of the optimized bifunctional electrocatalyst at -0.7 V for 8 h was tested, in which the CO/H₂ ratio was maintained between 1.2 and 1.3, indicating excellent stability. This study provides a new perspective for the engineering of bifunctional electrocatalysts for the conversion of abundant CO₂ and water into syngas with tailorable CO/H₂ ratios.

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM), common incurable diseases caused by protein misfolding, have shown extensive correlation with each other via cross-aggregation between their related pathogenic peptide, amyloid β protein (Aβ) and human islet amyloid polypeptide (hIAPP), respectively. However, little is known about how these two peptides affect the cross-amyloid aggregation process in vivo. To better simulate the intracorporal environment, where different forms of amyloid aggregates co-exist and very few aggregates probably attach to the vessel wall as seeds, herein, we study the seeded-aggregation of Aβ and hIAPP in the presence of homogeneous or heterogeneous seeds, both in solution and on the solid surface, with different monomer and seed concentrations. In this study, Thioflavin T (ThT) fluorescence assay, atomic force microscopy (AFM), and far-UV circular dichroism (CD) were performed to investigate the aggregation process in solution. Moreover, the binding of monomers with seeds on solid surface was detected by quartz crystal microbalance with dissipation (QCM-D). The 3-(4, 5-dime-thylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays with human neuroblastoma cells (SH-SY5Y) were finally used to test the cytotoxicity caused by the aggregates. Series of analyses confirmed that a small amount of Aβ40 or hIAPP seeds (1/50 of the monomers in solution) significantly changed the aggregation pathway, forming heterogeneous aggregates with different morphologies and increased β-sheet structures. MTT result showed that the heterogeneous aggregates obtained with Aβ40 and hIAPP seeding reduced the cell viability to 70.5% and 74.4%, respectively, both causing higher cytotoxicity than homogeneous aggregates (82.9% and 76.5%, respectively). The results in solution and on the solid surface both prove that Aβ40 and hIAPP seeds can not only induce rapid aggregation of their homogeneous monomers but also promote the heterogeneous monomers to aggregate, but monomer-heterogeneous seed binding efficiency is lower than that between homogeneous species. The differences in seeding and cross-seeding ability of Aβ40 and hIAPP indicate the barriers depended on the sequence similarity and structural compatibility between different amyloid aggregates. In the case of heterogeneous aggregation, aggregation features largely depend on the seeds. Furthermore, hIAPP seeds exhibited higher cross-seeding efficiency than Aβ40 seeds on the solid surface, which is different from the result in solution where Aβ40 seeds indicating the influence of interfacial properties on aggregation process. This finding would give a deep understanding of the cross-seeding aggregation process and we hope that this work will stimulate more research to explore all possible fundamental and practical aspects of amyloid cross-seeding.

HfO₂-based ferroelectric capacitors, particularly TiN/Hf_xZr_1-xO₂/TiN metal insulator metal (MIM) capacitors, have attracted considerable attention as promising candidates in the new generation of nonvolatile memory applications, because of their excellent stability, high performance, and complementary metal oxide semiconductor (CMOS) compatibility. At the electrode interface of TiN/Hf_xZr_1-xO₂/TiN MIM ferroelectric devices, the existence of the TiO_xN_y layer, which was formed during Hf_xZr_1-xO₂ film crystallization and TiN oxidization, can affect interface/grain boundary energy, film stress, and conduction band offset at the TiN/Hf_xZr_1-xO₂ interface, thereby affecting the ferroelectric device performance. Because the electrical performance of TiN/Hf_xZr_1-xO₂/TiN capacitors depends on both the ferroelectric Hf_xZr_1-xO₂ thin films and electrode TiN/insulator Hf_xZr_1-xO₂ interface, it is essential to control the fabrication of the TiN/Hf_xZr_1-xO₂/TiN heterostructure. Herein, we report a new method for preparing Hf_xZr_1-xO₂ ferroelectric thin films, sandwiched between TiN electrodes, by atomic layer deposition (ALD) and using ultra high vacuum (UHV) sputtering equipment interconnected with an ultra-high vacuum system. The quasi in situ characterization by transmission electron microscopy (TEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and other analytical methods conducted in our study indicates that the surface of the bottom TiN electrode does not contain oxygen. Moreover, a flat signal for impurities at the interface suggests that the superior ferroelectric performance of Hf_xZr_1-xO₂-based device is mainly attributed to the pristine Hf_xZr_1-xO₂/TiN interface. Furthermore, the ferroelectric properties of TiN/Hf_xZr_1-xO₂/TiN heterostructures on silicon can be modulated by varying ZrO₂ doping concentration and rapid thermal annealing (RTA) temperature, which can be well monitored and controlled by the interconnected system. We also investigate the ferroelectric properties of TiN/Hf_xZr_1-xO₂/TiN capacitors with different ZrO₂ doping concentrations (30%–60% (x)) at room temperature by changing the ALD pulsing ratio within the vacuum interconnected system. Three identical 10 nm-thick Hf_0.5Zr_0.5O₂ samples sandwiched between TiN electrodes are annealed in N₂ ambient at 400, 450 and 600 ℃ for 5 min to investigate the effect of RTA on device performance. The evolution of P-E hysteresis at different applied voltages and RTA temperatures reveals that the saturation of P-E hysteresis and remanent polarization increase with RTA temperature. This increase is especially evident at low applied voltages such as 1.5 V. A higher remanent polarization of 21.5 μC·cm^-2 than the previously reported value and a low coercive voltage of 1.35 V were achieved for the electric field of 3 MV·cm^-1 by doping 50% (molar fraction, x) ZrO₂ in HfO₂ through RTA at 600 ℃ for film crystallization.

Catalytic hydrogenation of CO₂ to methanol has attracted considerable attention due to its potential in alleviating global warming and mitigating the dependence on fossil fuels. Cu-based catalysts are widely used in industry because of their high activity for methanol production. However, the reaction still suffers from low methanol selectivity because of the generation of CO as a by-product via the reverse water gas shift reaction (RWGS). The formation of another by-product H₂O leads to inevitable Cu sintering, which decreases the methanol production rate. It is well known that CO can alter competitive molecular adsorption on the surface and the redox behavior of the active sites; hence, CO doping in feed gas might not only inhibit the RWGS but also minimize surface poisoning by the adsorbed oxygen. On the other hand, CO₂ hydrogenation to methanol over Cu-based catalysts is a structure-sensitive reaction, and a change in the precursor can have a remarkable influence on the structure and morphology of the catalyst, and ultimately, the catalytic performance. In this work, Cu/ZnO/Al₂O₃ catalysts have been prepared via a hydrotalcite-like precursor (CHT-CZA) and a complex phase precursor (CNP-CZA) using co-precipitation and ammonia evaporation methods. Subsequently, the performance of the two types of catalysts with different CO contents (CO₂: CO:H₂:N₂ = x:(24.5 - x):72.5:3) is compared at 250 ℃ and 5 MPa in order to explore the role of CO. The evaluation results show that both catalysts follow a similar trend in the conversion of CO and CO₂ as well as the space-time-yield (STY) of MeOH and H₂O. The conversions of CO₂ and STY_H2O decrease gradually with an increase in the CO volume, but STY_MeOH is positively correlated with the CO volume. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis reveals that the amount of reduced Cu species on the surface increases with increasing CO content. Judging from these results, the introduction of CO inhibits the RWGS and enhances the methanol yield for both catalysts by removing the surface oxygen as the reducing agent and thereby facilitating the exposure of the active reduced Cu species. On the other hand, transmission electron microscopy (TEM) observations indicate the doped CO may cause agglomeration of particles due to over-reduction, leading to gradual catalyst deactivation. Compared with the traditional CNP-CZA, the catalyst derived from hydrotalcite-like compounds exhibits better activity and long-term stability under all atmospheres, at different CO doping levels. This is because the hydrotalcite-like layer structure helps maintain the active metal state and confine the structure by limiting the agglomeration of Cu species.

Black phosphorus (BP) is a promising candidate for photovoltaic and optoelectronic applications owing to its excellent electronic and optical properties. It is believed that defects generally accelerate non-radiative electron-hole recombination in BP and hinder improvement of device performance. Experiments defy this expectation. Using state-of-the-art ab initio time-dependent density functional theory combined with non-adiabatic molecular dynamics, we investigate the non-radiative electron-hole recombination in monolayer (MBP) and MBP containing nanopore defects (MBP-ND). We demonstrate that non-radiative electron-hole recombination is promoted by the P-P stretching vibrations, and the recombination time of MBP-ND is approximately 5.5 times longer than that of the MBP system. This is mainly attributed to the following three factors: First, the nanopore creates no mid-gap state when increasing the bandgap by 0.22 eV owing to the downshift of the valence band maximum, caused by the decrease in the inter-layer P-P bond length, thereby weakening the antibonding interaction. Second, the nanopore reduces the overlap of electron and hole wave functions by diminishing the charge densities near the defect. Simultaneously, the nanopore significantly inhibits the thermal-driven atomic fluctuations. The increased bandgap correlated with the decreased wave function overlap and slowed thermal motions of the nuclei in the MBP-ND system reduces the non-adiabatic coupling by a factor of approximately 2 with respect to the pristine system. Third, the slow atomic motions weaken the electron-vibrational interaction and decrease the intensity of the major vibration mode at 440 cm⁻¹, which is the main source for creating non-adiabatic coupling, leading to loss of coherence formed between a pair of electronic states via non-adiabatic coupling and causing electron-hole recombination that results in a 1.5-fold increase in the coherence time in the MBP-ND system with respect to the MBP system. Consequently, the increased bandgap and decreased non-adiabatic coupling compete successfully with the prolonged coherence time, extending the excited-state lifetime to 2.74 ns in the system containing nanopore defects, which is only 480 ps in the pristine system. These phenomena arise owing to a complex interplay of the unusual chemical, structural, electrostatic, and quantum properties of BP with and without nanopore defects. This study is of great significance for understanding the excited-state properties of BP. The detailed mechanistic understanding of the prolonged charge carriers lifetime of MBP decorated with nanopore defects provides key insights for defect engineering in BP and other 2-dimensional materials for a broad range of solar and electro-optic applications by reducing the non-radiative charge and energy losses.

Surfactants are widely applied for promoting miscibility and reducing interfacial tension between oil and water phases because of their remarkable amphiphilic morphology. Along with development and popularization of tertiary oil recovery techniques, surfactants play a significant role in crude oil exploitation. Among the various tertiary oil recovery techniques, supercritical CO₂-enhanced oil recovery is a promising method for improving oil recovery. However, the establishment of CO₂-enhanced oil recovery brought new requirements and challenges to traditional surfactant research and development, especially for molecular design. In this method, the reduction of the minimum miscibility pressure between supercritical CO₂ and crude oil is required to achieve miscible flooding—an important means to enhance oil recovery. Therefore, a novel miscible flooding agent that exhibits oil-water miscibility analogous to conventional surfactants is desirable for this method. Meanwhile, a conspicuous difference of polarity matching the high polarity of H₂O molecule against low polarity of alkane molecule, which is the essential feature of traditional surfactant, won't suit this case well due to a medium polarity of CO₂ molecule. According to previous work done in our laboratory, surfactants with multiple ester groups considerably reduce the minimum miscibility pressure between supercritical CO₂ and crude oil. Therefore, inspired by the "oil-water-amphiphilic molecules" design, herein, we replaced the hydrophilic moiety with multiple ester groups and designed a new type of "oil-CO₂ amphiphilic molecule" as a miscible flooding agent, which is composed of an alkane tail and multiple ester groups as the lipophilic and CO₂-philic groups, respectively. In the strategy based on the proposed agent, the number of ester groups and the length of the alkane tail are the main parameters. In addition, we optimized the molecular structure of the proposed agent, CAA8-X, which comprises cetyl and acetyl sucrose esters as the lipophilic and CO₂-philic groups, respectively. We verified that the as-synthesized agent can remarkably reduce the minimum miscibility pressure between supercritical CO₂ and various types of oil samples, including kerosene, white oil, and crude oil from the Changqing region. The crude oil-CO₂ minimum miscibility pressure reduction ratio was 20.5% as measured by the vanishing interfacial tension method and the slim tube test. In this study, we also established a method called the rising height method to measure the minimum miscibility pressure with significantly reduced time and equipment cost. Furthermore, to demonstrate the mechanism of this miscible flooding agent for CO₂-enhanced oil recovery, the affinity between the CO₂-philic group and molecular CO₂ was investigated via molecular dynamics simulation. The results indicated that the "oil-CO₂ amphiphilic molecule" can reduce oil-CO₂ interfacial tension because of lower affinity potential energy between the CO₂-philic group and molecular CO₂.

The molecular magnetic tunnel junction (MMTJ) with high tunnel magnetoresistance (TMR) is an important component for devices such as computers and electronic storage. With the rapid development of the modern electronics industry, the decrease of device size and the increase of area density, it is important to improve TMR technology. In addition, the computing process faces huge challenges. As the size of electronic devices decreases, small changes may cause completely different transmission characteristics, therefore the minute details of the device must be carefully controlled. In this paper, in order to find large TMR values and explore the role of symmetry on spin-polarized transport properties, γ-graphyne nanodots (γ-GYND) coupled between ferromagnetic (FM) metallic zigzag graphene nanoribbon (ZGNR) electrodes were used. Depending on the widths of the ZGNR and two types of contact positions between the ZGNR and γ-graphyne nanodots (γ-GYND), eight ZGNR/γ-GYND/ZGNR MMTJs with different symmetries were constructed. By using Keldysh non-equilibrium Green's function (NEGF) and density functional theory (DFT), the I-V curve, the spin-injection efficiency (SIE) and TMR of MMTJs were calculated. We found that the transport properties of these MMTJs differed substantially. For absolute symmetric MMTJs, due to the wave functions corresponding to the band structure near the Fermi energy having different parity, the electron transport between the wave functions with different parity is prohibited, so we can see that the spin-down current is always zero. This implies that these absolutely symmetrical structures have 100% spin injection efficiency over a wide range of bias voltages. In addition, the calculation results also show that these absolutely symmetric structures also have large TMR at low bias, up to 3.7 × 10⁵, indicating that these devices have a large magnetoresistance effect and high magnetic field sensitivity, which can be used in the read head of computer hard disks, MRAM, and various magnetic sensors. However, for these asymmetric MMTJs, since there is no limitation of the wave function parity of the left and right electrodes, the spin-up current and spin-down current fluctuated as the bias voltage increased, so perfect SIE does not appear. In addition, the calculation results showed that the TMR of asymmetric MMTJs were four orders of magnitude smaller than with symmetric MMTJs. Thus the symmetry of MMTJs has a great influence on the spin-polarized transport properties of the device. These absolutely symmetrical MMTJs have spin-polarized transport properties that are far superior to other MMTJs. This is conducive to the manufacture of spin filters, rectifiers, and various magnetic sensors. Finally, these excellent characteristics can be explained by the transmission coefficient, local density of states (LDOS) and band structure.

The interfacial mass transfer characteristics of the gas-oil miscibility process are important in gas flooding technology to improve oil recovery. In this study, the process of gas flooding with actual components of Jilin oilfield is investigated by using molecular dynamics simulation method. We have chosen several alkane molecules based specifically on the actual components of crucial oil as the model oil phase for our study. The pressure of the gas phase is adjusted by changing the number of gas molecules while keeping the oil phase constant in the simulation. After the simulation, we analyze the variations of density in the gas-oil phase and interfacial characteristics to obtain the minimum miscibility pressure (MMP) for different displacement gases. The results show that the density of the gas phase increases while the density of the oil phase decreases with an increase in the displacement gas pressure, resulting in efficient mixing between the gas phase and the oil phase. At higher gas pressures, the thickness of the interface between the gas and oil phases is higher while the interfacial tension is lower. At the same time, we observed that the higher the CO₂ content in the displacement phase, the thicker the oil-gas interface becomes and the better the oil-gas mixing is under the same gas pressure. In this work, the gas-oil miscibility is studied with pure CO₂, pure N₂, and the mixture of these two gases, and it is found that the minimum miscibility pressure for pure CO₂ flooding (22.3 MPa) is much lower than that for pure N₂ flooding (119.0 MPa). When these two gases are mixed in 1 : 1 ratio, the MMP (50.7 MPa) is between the MMPs of the two pure gases. Moreover, the pressure required with CO₂ is lower than that required with N₂ to achieve the same displacement effect. Finally, we explain the mechanisms of the different miscibility processes for different gas pressure and different displacement gases from the perspective of the total energy of the system and the potential of the mean force between the gas and the oil. The total energy of the system increases with the pressure of the gas phase, implying that the number of collisions between the oil and gas molecules increases and the gas-oil miscibility is enhanced. In addition, by analyzing the potential of mean force profiles, it can be concluded that the force of attraction between the oil-phase molecules and CO₂ molecules is greater than that between the oil-phase molecules and N₂ molecules; thus, the CO₂ molecules easily mix with oil, and the effect of displacement is more obvious. These results are of great significance for understanding the interfacial mass transfer characteristics of the gas-oil miscibility process and for guiding the optimization and design of enhanced oil recovery technology by gas flooding.

Graphene-wrapped natural spherical graphite (G/SG) composites were prepared using the encapsulation–carbonization approach. The morphology and structure of the composites were characterized by scanning electron microscopy and X-ray diffraction analysis. The electrochemical performance of the composites with different graphene contents as anode materials for lithium-ion batteries was investigated by various electrochemical techniques. In the absence of acetylene black (AB), the G/SG composites were found to exhibit high specific capacity with high first-cycle coulombic efficiency, good cycling stability, and high rate performance. Compared with the natural spherical graphite (SG) electrode, the G/SG composite electrode with 1% graphene exhibited higher reversible capacity after 50 cycles; this capacity performance was equal to that of the SG + 10%AB electrode. Moreover, when the addition of 2.5% graphene, the composite electrode exhibited higher initial charge capacity and reversible capacity during 50 cycles than the SG+10%AB electrode. The significant improvement of the electrochemical performance of the G/SG composite electrodes could be attributed to graphene wrapping. The graphene shell enhances the structural integrity of the natural SG particles during the lithiation and delithiation processes, further improving the cycling stability of the composites. Moreover, the bridging of adjacent SG particles allows the formation of a highly conductive network for electron transfer among SG particles. Graphene in the composites serves as not only an active material but also a conductive agent and promotes the improvement of electrochemical performance. When 5%AB was added, the reversible capacity of the 5%G/SG electrodes significantly increased from 381.1 to 404.5 mAh·g^-1 after 50 cycles at a rate of 50 mA·g^-1 and from 82.5 to 101.9 mAh·g^-1 at 1 A·g^-1, suggesting that AB addition improves the performance of the G/SG composite electrodes. AB particles connect to G/SG particles through point contact type and fill the gaps between G/SG. A more effective conductive network is synergistically formed via graphene-AB connection. Although graphene wrapping and AB addition improve the performance of natural graphite electrodes, such as through increase in electrical conductivity and enhancement of Li-storage performance, including improvement of reversible capacity, rate performance, and cycling stability, electrode density typically decreases with graphene or AB addition, which should consider the balance between the gravimetric and volumetric capacities of graphite anode materials in practical applications. These results have great significance for expanding the commercial application scope of natural graphite. Our work provides new understanding and insight into the electrochemical behavior of natural SG electrodes in lithium-ion batteries and is helpful for the fabrication of high-performance anode materials.

With the development of clean energy sources such as solar and wind power, large-scale energy storage technologies will play a significant role in the rational utilization of clean energy. Sodium ion batteries have garnered considerable attention for large-scale energy storage owing to their low cost and the presence of abundant sodium resources. It is particularly crucial to develop electrode materials for sodium battery with good rate capability and long cycle life. Orthogonal-phase niobium oxide (T-Nb₂O₅) exhibits good potential to be used as anode material for sodium-ion batteries owing to its high theoretical specific capacity (200 mAh·g⁻¹) and high ionic diffusion coefficient. Furthermore, it demonstrates a better performance than that of graphite and exhibits a higher specific capacity than that of Li₄TiO₄ when used in sodium-ion batteries. However, its poor electrical conductivity has hindered its practical application. Recently, effective strategies such as coating with carbon materials or metal conductive particles have been developed to overcome this issue. Although the electrochemical performance of T-Nb₂O₅ has been improved, the sodiation mechanism of T-Nb₂O₅ is still unclear. It is considered to be similar to the lithium mechanism wherein lithium ions diffuse rapidly on the (001) planes, but exhibit difficulty in diffusing across the (001) planes. In this study, the electrochemical sodiation behaviors along the (001) lattice planes and the [001] direction of the T-Nb₂O₅ nanosheet are studied by in situ transmission electron microscopy (TEM). The results indicate that there are a large number of dislocations and domain boundaries in nanocrystals. Furthermore, it was observed that, sodium ions can diffuse across the (001) lattice planes through these defects, and then diffuse rapidly on the (001) planes. Meanwhile, we found a modulation structure in the [001] direction of the original nanosheet, in which alternating compressive and tensile strains were observed. These strain distributions can be regulated by the insertion of sodium ions, while the modulation structure is maintained. Moreover, the in situ TEM method used in this work can be applied to various energy materials.

Redox flow batteries (RFBs) have been widely recognized as the primary choice for large-scale energy storage due to their high energy efficiency, low cost, and versatile design of decoupled energy storage and power output. However, the broad deployment of RFBs in the power grid has long been plagued by the high cost and low energy density of existing inorganic metal-based electrodes. Redox-active organic molecules (ROMs), on the other hand, have recently been extensively explored as the potentials electrodes in RFBs for their potential low cost, abundant resources, and highly tunable structure. The energy density of RFBs is proportional to the number of electrons transferred per unit reaction, the concentration of active materials, and the cell voltage. Therefore, strategies to improve the energy density of RFBs could be categorized into three classes: (1) expanding the cell voltage; (2) maximizing the practical concentration of active materials; (3) realizing multi-redox process. Benefited by the highly tunable structure and properties of ROMs, the cell voltage of RFBs could be realized by lowering the redox potentials of anolytes or/and increasing the redox potentials of catholytes. To fully exploit the low-potential anolytes and high-potential catholytes, non-aqueous electrolytes with wider electrochemical potential windows (EPWs) are preferred over the aqueous systems. However, the solubility of most ROMs in commonly used non-aqueous electrolytes is very limited. Several effective strategies to improve the practical concentrations of ROMs have been proposed: (1) the solubility of ROMs could be easily tailored by adjusting the intermolecular interactions between ROMs and the interactions between ROMs and electrolytes via molecular engineering; (2) the redox-active eutectic systems remain liquid at or near room temperature, allowing us to reduce or completely remove the inactive solvent used in the conventional electrolyte of RFBs, which leads to an enhanced practical concentration of the redox-active components; (3) the semi-solid suspension achieves a high practical concentration of ROMs by combining the advantages of solid ROMs with high energy density and liquid electrolytes with flowability; (4) the redox-targeting approach breaks the solubility limitation by realizing remote charge exchange between the solid active materials deposited in the tanks and the current collectors of the electrochemical stacks via ROMs dissolved in electrolytes. The first three strategies employ a homogeneous flowing redox-active fluid which suffers from deteriorated physical and electrochemical properties as the practical concentration of ROMs increase, e.g., high viscosity, phase separation, and salt precipitation. The redox-targeting approach uses a hybrid flowing liquid/static solid system, which avoids the aforementioned unfavorable changes in electrolyte properties, however, this design introduces additional chemical reactions between the ROMs and the solid active materials, which may reduce the power output. Another efficient method to improve the energy density of RFBs without affecting the properties of the electrolyte is achieved by realizing the multi-redox process of ROMs, however, the generated high valence state ROMs are highly reactive. Further optimization of the structure of these ROMs is required to improve their lifetime at high valence states. In this perspective, we summarize the general working principle of the RFBs, highlight the recent developments of the ROMs in non-aqueous redox flow batteries (NRFBs), with an emphasis on the strategies to improve the energy density of NRFBs, and discuss the remaining challenges and future directions of the non-aqueous organic redox flow batteries (NORFBs).

The diameter-controlled growth of single-walled carbon nanotubes (SWNTs) is one of the key issues of SWNT synthesis and application. To guarantee that SWNTs grow with desired diameters, it is necessary to control catalyst size and modulate growth conditions. SWNTs with diameters of 0.9–1.2 nm are highly desirable for near-infrared fluorescence bioimaging and serving as effective single-photon sources for the development of quantum devices. Herein, we used an FeCo/MgO catalyst to grow bulk SWNTs with diameters in the range and studied the influence of catalysts and chemical vapor deposition (CVD) growth conditions on the diameter of SWNTs. The preparation of catalyst precursors is a key step in obtaining catalyst nanoparticles of small size. In the impregnation process, we used three different types of metal salts, namely, sulfates, acetates, and nitrates, to prepare the catalysts. The metal sulfates, which exhibit the weakest hydrolysis ability, were found to grow SWNTs with the smallest diameters. Lowering the immersion pH, which suppresses the hydrolysis of metal ions, was also favorable for growing smaller SWNTs. Moreover, the addition of complexing agent molecules such as ethylenediaminetetraacetic acid during the impregnation process, which inhibits the hydrolysis of metal ions as well, further confined the diameter distribution of the resultant SWNTs. During the solution drying process, metal salts hydrolyze into metal hydroxides and oxides. Under mild hydrolysis conditions, the produced hydroxide and oxide particles are smaller and more likely to be uniformly distributed on the surface of the supports. Therefore, it is more favorable to produce catalysts with controlled sizes under mild hydrolysis conditions, which are preferred for diameter control of the resultant SWNTs. In the CVD growth process, we used either ethanol or methane as the carbon source and found that, under our experimental conditions, the SWNTs grown from ethanol had smaller diameters than those from methane. The hydrogen content in the CVD process also affects diameter distribution of SWNTs. As the carbon-to-hydrogen ratio decreased, SWNTs with larger diameters disappeared, and the number of SWNTs with smaller diameters increased. During the CVD process, the carbon-to-hydrogen ratio determines the carbon feeding rate to the catalysts. At a low carbon feeding rate, catalysts of large sizes are underfed and unable to grow SWNTs, whereas smaller catalysts are in a favorable condition for growth. Therefore, the average diameter of the SWNTs decreased as the carbon-to-hydrogen ratio decreased.

Corrosion protection of reinforcing steel in concrete is an urgent task in modern society. Use of corrosion inhibitors in concrete is an effective, simple, and economical method for protecting reinforcing steel from corrosion. Mixed corrosion inhibitors usually perform better than a single inhibitor in actual reinforced concrete systems because of their synergistic inhibition effects. In recent years, environmentally friendly corrosion inhibitors have attracted increasing attention from corrosion researchers. Diisooctyl sebacate and sodium D-gluconate are environmentally friendly organic corrosion inhibitors, and ZnSO₄ is an inorganic cathodic inhibitor, they may form an innovative, nontoxic, and pollution-free mixed corrosion inhibitor to control reinforcing steel corrosion. Additionally, diisooctyl sebacate and sodium D-gluconate serve as absorption-type inhibitors, and ZnSO₄ acts as a precipitation-type inhibitor. We hypothesized that their combination might show a good synergistic corrosion inhibition effect on reinforcing steel. In this study, we developed a diisooctyl sebacate-based mixed corrosion inhibitor that includes D-gluconate and ZnSO₄ and investigated its synergistic inhibition effects on reinforcing steel (Q235 steel) corrosion in a simulated polluted concrete pore solution. The reinforcing steel corrosion behavior and the properties of the mixed corrosion inhibitor were studied by polarization curve measurements, electrochemical impedance spectroscopy tests, and surface analysis methods (scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy). The results indicated that the reinforcing steel in the simulated polluted concrete pore solution (pH 11.00, 0.5 mol·L^-1 NaCl) was in an active dissolving state and that localized corrosion took place. The mixed corrosion inhibitor, consisting of diisooctyl sebacate (59 mmol·L^-1), sodium D-gluconate (0.5 mmol·L^-1), and ZnSO₄ (1.5 mmol·L^-1), had an obvious and powerful inhibition effect. Its inhibition efficiency reached 96.8% and 90.0% in the simulated polluted concrete pore solution and the cement mortar, respectively. The mixture of diisooctyl sebacate with sodium D-gluconate and ZnSO₄ acted as a mixed-type inhibitor and effectively controlled both anodic and cathodic reactions of the steel corrosion.

The development of new types of artificial muscles is of utmost importance as traditional actuators based on mechanical drive systems no longer meet the stringent requirements of flexibility, high efficiency, and multi-stimuli responses in advanced functional fields, such as soft and biomimetic robots, sensors, artificial intelligent control, and artificial intelligence. Carbonene materials refer to carbon materials composed of all carbon atoms with sp² hybridization, mainly including carbon nanotubes and graphene. Owing to their exceptional properties such as light weight, excellent mechanical performance, high conductivity, flexibility, and large specific surface area, carbonene materials demonstrate significant application potential in artificial muscles, thereby promoting the rapid development of corresponding fields. Herein, the recent progress of the application of carbonene materials in artificial muscles is summarized to provide a comprehensive understanding of the preparation, properties, and applications of artificial muscles composed of carbonene materials. First, carbonene artificial muscles integrating response, actuation, and structure are introduced. As carbonene materials are unique building blocks that can be readily assembled into macroscopic materials with various structures, fibrous and membranous artificial muscles based on carbonene materials are discussed in detail. Carbonene fiber actuators demonstrate diverse actuation performances when fabricated with different structures. Bending actuation typically occurs when carbonene artificial muscles with asymmetric structures are subjected to external stimulation. The untwisting of carbonene artificial muscle fibers with twisted structures causes torsional and tensile actuation, which can be attributed to the volume expansion induced by external stimuli. Furthermore, coiled structures achieved by twisting a fiber until it is fully coiled can enhance the actuation stroke. Thus, the actuation of artificial muscle fibers made of carbonene materials can be classified into bending, rotation, and contraction actuations. Second, carbonene materials have long been considered as a functional component in composite materials for specific applications owing to their excellent physical and chemical properties. Therefore, the application of carbonene materials as an additional component to other artificial muscle materials (such as smart hydrogels, dielectric elastomers, and conducting polymers) is reviewed. By employing carbonene materials, artificial muscle materials exhibit improved electrical and mechanical properties, thereby leading to superior actuation performances. In addition, integrating carbonene materials into artificial muscles can endow the muscles with programmable actuation and sensing functions. Finally, the challenges faced in the application of artificial muscles based on carbonene materials and the future application of carbonene artificial muscles with multi-functional actuation performance are briefly discussed.

Carbon nanotube fiber (CNTF) comprises continuous yarn-like macro aggregates with a large amount of carbon nanotubes and bundles thereof. CNTFs have excellent properties, such as high strength, toughness, and conductivity, because of which, they have broad prospects in several fields, such as structure-function integrated composite materials, fibrous energy devices, artificial muscle, and lightweight conductive wire. After two decades of development, breakthroughs have been made in continuous preparation technology, performance enhancement, and application exploration of CNTF materials. In this review, the development history of CNTF materials is summarized, and various continuous preparation technologies of CNTFs, including wet spinning, array spinning, and floating catalyst chemical vapor deposition (FCCVD) direct spinning, are described and compared. The wet spinning technology for fabricating CNTFs can be easily scaled due to its similarity to the conventional wet spinning technology used for fabricating high-performance fibers, while the obtained CNTFs have relatively high conductivity. The main challenges in wet spinning are the mass preparation and appropriate dispersion of high-quality carbon nanotubes (CNTs) with large aspect ratios. The array spinning technology can produce CNTFs with high purity and controllable structures, and its challenges are the relatively low preparation efficiency and high cost, because of which, it is challenging to meet the needs of large-scale applications. The FCCVD direct spinning technology can continuously produce CNTFs with relatively high strengths and at low cost, and it is easily adaptable for large-scale fabrication. The main drawbacks of CNTFs obtained from direct spinning are the relatively high impurity content and nonuniform CNT structures. Since CNTFs were first reported in 2000, one of the major challenges has been transferring the excellent properties of individual CNTs to the macroscopic assemblies of CNTs. To answer this question, the correlation between the structures and properties of CNTFs is discussed in detail, and contemporary techniques used for the enhancement of mechanical and electrical properties of CNTFs are reviewed. Based on the fiber fracture mechanism of slippage between CNTs, typical mechanical performance enhancement techniques include manipulating the CNT structures (namely wall number, diameter, aspect ratio, and collapse state), aligning the CNT along the fiber axis, enhancing the packing density and the interaction between CNTs, and combining with other reinforcing materials. The electrical performance of CNTFs is attributed to a 3D hopping electron transport mechanism in CNTFs. Conductivity enhancement techniques mainly include improving the assembly structure of CNTFs, using conductive materials as fillers between the CNTs, oxidative p-doping, and combining with metallic conductors. Finally, the main challenges in terms of performance enhancement and large-scale fabrication are discussed, and the development directions of CNTF materials are proposed.

Quantum dot light-emitting diodes (QLEDs) constitute the next-generation display technology because of their wide color gamut, narrow emission spectrum, adjustable emission wavelength, and ease of solution processability. With the development of novel material and device preparation techniques, the QLEDs not only show an external quantum efficiency (EQE) of more than 20% in red, green, and blue (primary color) devices, but also achieve 100% Rec.2020 (recommendation standard for ultrahigh-resolution display) color gamut coverage. However, the future commercialization of QLEDs is still a challenge. The T95 lifetime (defined as 95% time for the luminance to decay to the initial value L₀ = 1000 cd·m^-2) of red, green, and blue QLED devices is significantly lower than that of commercially available organic light-emitting diodes (OLEDs). This is ascribed to the lacking of understanding and argument to hypothesis of degradation mechanisms. A QLED is a sandwich structure composed of a quantum dot (QD) emitter layer, carrier transport layer, and electrode layer. The QLED works on the principle of electroluminescence: electrons and holes injected from the electrodes on both sides of the device cross multiple interfaces and reach the QD emitter layer to undergo radiation recombination. Generally, the QD emitter layer adopts the structure of a wide-band gap shell wrapped around a narrow band-gap core. Because of the deep valence band maximum, the hole injection barrier is higher, and the hole injection efficiency is reduced. This not only disturbs the injection balance but also leads to the accumulation of interfacial holes, which is one of the important factors affecting the efficiency and life of the device. Past studies have attempted to understand charge accumulation behavior in QLEDs by predicting the interfacial energy band structure, and there are very few reports on the direct measurement of charge accumulation. In this work, we built a charge extraction circuit to investigate the charge accumulation behavior before and after aging in a prototype red QLED. In the fresh red QLEDs, the number of accumulated charges gradually increased with the driving current density and tended to saturate above turn-on current density. In the aged red QLEDs, the accumulated charges increased with a decrease in luminance. Our method to investigate the charge accumulation behavior developed can be extended to various kinds of LEDs, such as OLEDs and perovskite LEDs, thus providing insight into their working mechanism.

Hydrogen (H₂) is an important component in the framework of carbon-neutral energy, and the scalable production of H₂ from seawater electrolysis offers a feasible route to address global energy challenges. With abundant seawater reserves, seawater electrolysis, especially when powered by renewable electricity sources, has great prospects. However, chloride ions (Cl^-) in seawater can participate in the anodic reaction and accelerate the corrosion of electrode materials during electrolysis. Although the oxygen evolution reaction (OER) is thermodynamically favorable, the chlorine evolution reaction is highly competitive because fewer electrons are involved (2e^-). These two problems are compounded by the dearth of corrosion-resistant electrode materials, which hinders the practical applications of seawater electrolysis. Therefore, intensive research efforts have been devoted to optimizing electrode materials using fundamental theories for practical applications. This review summarizes the recent progress in advanced electrode materials with an emphasis on their selectivity and anti-corrosivity. Practical materials with improved selectivity for oxygen generation, such as mixed metal oxides, Ni/Fe/Co-based composites, and manganese oxide (MnO_x)-coated heterostructures, are reviewed in detail. Theoretically, alkaline environments (pH > 7.5) are preferred for OER as a constant potential gap (480 mV) exists in the high pH region. Nevertheless, corrosion of both the cathode and anode from ubiquitous Cl^- is inevitable. Only a few materials with good corrosion resistance are capable of sustained operation in seawater systems; these include metal titanium and carbon-based materials. The corrosion process is usually accompanied by the formation of a passivated layer on the surface, but the aggressive penetration of Cl^- can damage the whole electrode. Therefore, the selective inhibition of Cl^- transport in the presence of a robust layer is critical to prevent continuous corrosion. Advances in anti-corrosion engineering, which encompasses inherently anti-corrosive materials, extrinsically protective coating, and in situ generated resistive species, are systematically discussed. Rational design can impart the material with good catalytic activity, stability, and corrosion resistance. Finally, we propose the following opportunities for future research: 1) screening of selective and anti-corrosive materials; 2) mechanism of competitive reactions and corrosion; 3) evaluation of anti-corrosive materials; 4) industrial-scale electrolysis with high current density; 5) optimization of experimental conditions; and 6) development of integrated electrolyzer devices. This review provides insights for the development of strategies aimed at tackling chlorine-related issues in seawater electrolysis.

Graphene fiber, a macroscopic one-dimensional material formed by assembling elementary graphene flakes, has emerged in response to the increasing demand for multifunctional or even smart fibers. Based on the astonishing properties of graphene building blocks, graphene fiber presents a series of attractive features, such as superior mechanical strength and electronic conductivity, light-weight, and efficient thermal conductivity. As a result, graphene fiber exhibits broad prospects for application in ultralight cables for aerospace, wearable energy storage devices, biosensors, and neuroelectronics. graphene fiber may provide a critical breakthrough for realizing multi-functional fibers or even smart textiles. Since it was first prepared in 2011, numerous fabrication techniques have been developed to assemble graphene fiber, such as wet spinning, space-confined hydrothermal assembly, film twisting approaches, and template-assisted chemical vapor deposition. Among various graphene fiber preparation approaches, wet spinning has great application potential, as it affords the best mechanical strength and electrical conductivity of the prepared graphene fiber, along with great compatibility with the commercialized wet spinning technique. Therefore, the wet spinning approach has attracted extensive attention for batch production of high-performance graphene fiber. Herein, we introduce the pivotal steps of the wet spinning preparation of graphene fiber, with focus on summarizing the detailed strategies for enhancing the fiber properties and we also discuss the relationship between the structure and assembly approaches. The wet spinning technology for assembling graphene fiber includes a series of critical steps, such as preparation of the spinning liquid, bath coagulation, spinneret design, and post-treatment process. These procedures may have a significant influence on the micro-, meso-, and macro-structure of the final prepared graphene fiber. We also discuss the fundamental relationship between the typical properties of graphene fibers and their hierarchical structures, such as the in-planar structure of graphene sheets, aggregation structure of graphene flakes, and the macrostructure or morphology of graphene fiber. The recent advances in graphene fiber-based smart fibers and fabric applications are also analyzed, highlighting possible strategies for promoting structural-functional integrated applications. Finally, the current challenges and possible approaches for further improving the mechanical and electric properties of graphene fiber are presented. This review can be briefly divided into three parts: (1) details of the wet spinning process and its specific influence on the structural features of graphene fiber, (2) characteristics of current graphene fibers and promising strategies for enhancing the properties, (3) latest studies of graphene fiber applications and perspectives for future application.

Photocatalytic hydrogen production is an effective strategy for addressing energy shortage and converting solar energy into chemical energy. Exploring effective strategies to improve photocatalytic H₂ production is a key challenge in the field of energy conversion. There are numerous oxygen vacancies on the surface of non-stoichiometric W₁₈O₄₉ (WO), which result in suitable light absorption performance, but the hydrogen evolution effect is not ideal because the band potential does not reach the hydrogen evolution potential. A suitable heterojunction is constructed to optimize defects such as high carrier recombination rate and low photocatalytic performance in a semiconductor. Herein, 2D porous carbon nitride (PCN) is synthesized, followed by the in situ growth of 1D WO on the PCN to realize a step-scheme (S-scheme) heterojunction. When WO and PCN are composited, the difference between the Fermi levels of WO and PCN leads to electron migration, which balances the Fermi levels of WO and PCN. Electron transfer leads to the formation of an interfacial electric field and bends the energy bands of WO and PCN, thereby resulting in the recombination of unused electrons and holes while leaving used electrons and holes, which can accelerate the separation and charge transfer at the interface and endow the WO/PCN system with better redox capabilities. In addition, PCN with a porous structure provides more catalytic active sites. The photocatalytic performance of the sample can be investigated using the amount of hydrogen released. Compared to WO and PCN, 20%WO/PCN composite has a higher H₂ production rate (1700 μmol·g^-1·h^-1), which is 56 times greater than that of PCN (30 μmol·g^-1·h^-1). This study shows the possibility of the application of S-scheme heterojunction in the field of photocatalytic H₂ production.

The rational interface tailoring of nanosheets on hollow spheres is a promising strategy to develop efficient photocatalysts for hydrogen production with solar energy. Among the various photocatalyst materials, metal sulfides have been extensively researched because of their relatively narrow band gap and superior visible-light response. ZnIn₂S₄ is a layered ternary chalcogenide semiconductor photocatalyst with a tunable band gap energy (approximately 2.4 eV). Among various metal sulfide photocatalysts, ZnIn₂S₄ has gained considerable attention. However, intrinsic ZnIn₂S₄ only exhibits a relatively moderate photocatalytic activity, which is mainly owing to the high recombination and low migration rate of photocarriers. Loading cocatalysts onto semiconductor photocatalysts is an effective way to improve the performance of photocatalysts, because it can not only facilitate the separation of electron-hole pairs, but also reduce the activation energy for proton reduction. As a ternary transition metal sulfide, NiCo₂S₄ features a high electrical conductivity, low electronegativity, excellent redox properties, and outstanding electrocatalytic activity. Such favorable characteristics suggest that NiCo₂S₄ can expedite charge separation and transfer, thereby promoting photocatalytic H₂ production by serving as a cocatalyst. Moreover, both NiCo₂S₄ and ZnIn₂S₄ possess the ternary spinel crystal structure, which may facilitate the construction of NiCo₂S₄/ZnIn₂S₄ hybrids with tight interfacial contact for an enhanced photocatalytic performance. Herein, ultrathin ZnIn₂S₄ nanosheets were grown in situ on a non-noble-metal cocatalyst, namely NiCo₂S₄ hollow spheres, to form hierarchical NiCo₂S₄@ZnIn₂S₄ hollow heterostructured photocatalysts with an intimately coupled interface and strong visible light absorption extending to ca. 583 nm. The optimized NiCo₂S₄@ZnIn₂S₄ hybrid with a NiCo₂S₄ content of ca. 3.1% exhibited a high hydrogen evolution rate of 78 μmol·h^-1, which was approximately 9 times higher than that of bare ZnIn₂S₄ and 3 times higher than that of 1% (w, mass fraction) Pt/ZnIn₂S₄. Additionally, the hybrid photocatalysts displayed good stability in the reaction. Photoluminescence and electrochemical analysis results indicated that NiCo₂S₄ hollow spheres served as an efficient cocatalyst for facilitating the separation and transport of light-induced charge carriers as well as reducing the hydrogen evolution reaction barrier. Finally, a possible reaction mechanism for the photocatalytic hydrogen evolution was proposed. In the NiCo₂S₄@ZnIn₂S₄ composite photocatalyst, the NiCo₂S₄ cocatalyst with high electrical conductivity favorably accepts the photoinduced electrons transferred from ZnIn₂S₄ and then employs the electrons to reduce protons for H₂ production on the reactive sites. Concurrently, the photogenerated holes are trapped by TEOA that acts as a hole scavenger to accomplish the photoredox cycle. This study provides guidance for the fabrication of hierarchical hollow heterostructures based on nanosheet semiconductor subunits as remarkable photocatalysts for hydrogen production.

Owing to their advantages such as safe operation, high power density, long cycle life, and low self-discharge rate, lithium-ion batteries (LIBs) have attracted attention for applications ranging from portable electronics to electric vehicles (EVs)/hybrid EVs (HEVs). However, the striking exothermic reaction and growth of lithium dendrites during lithiation-delithiation cycles for commercial graphite anodes are hidden safety risks associated with LIBs. Titanium dioxide (TiO₂) is considered as an important material for LIBs because of its high safety and excellent cycling stability. In addition, TiO₂ anode used in lithium-ion storage system has a relatively high voltage (~1.5 V vs. Li/Li⁺), and thus, it meets the strict safety standards of commercial LIBs. However, the unsatisfactory conductivity and ion diffusion rate prevent the further application of TiO₂ in LIBs. To date, the combination of graphene, carbon nanotubes (CNTs), carbon quantum dots (QDs) and porous carbon with TiO₂ has attracted significant research attention. Nevertheless, it is still challenging to introduce a unique nanostructure design by organically compounding TiO₂ with N-doped porous carbon matrix. Herein, N-doped porous carbon incorporating fine TiO₂ nanoparticles (NPs) with a flower-like structure (denoted as FL-TiO₂/NPC) is successfully prepared using flower-like NH₂-MIL-125(Ti) as the hard template. The as-prepared Ti-based framework shows a flower-like structure, which is assembled with two-dimensional (2D) corrugated porous nanosheets. On the one hand, the corrugated carbon nanosheets incorporating fine TiO₂ particles can offer a magnifying contact area between electrode matrix and electrolyte. On the other hand, the N-doped porous carbon plays a crucial role in improving the conductivity and structural integrity of the whole matrix. Therefore, the as-prepared FL-TiO₂/NPC can deliver an excellent reversible lithium storage capacity of 384.2 mAh·g^-1 at the current density of 0.5 A·g^-1 after 300 cycles and 279.1 mAh·g^-1 at 1 A·g^-1 after 500 cycles. Furthermore, even when tested at 2 A·g^-1, FL-TiO₂/NPC can deliver a reversible capacity of 256.5 mAh·g^-1 with a coulombic efficiency of 100% after 2000 cycles. The superior electrochemical performance and the structural toughness of LIBs originate from the unique flower-like structure. We believe that the proposed synthesis strategy will provide a new idea for the preparation of metal oxides/N-doped porous carbon composites with high lithium storage performance.

In recent years, flexible and wearable electronic devices have attracted increasing research, industrial, and consumer attention. In particular, flexible zinc-air batteries (ZABs) are expected to become a promising power supply source for next-generation electronic products, especially the flexible and wearable ones, because of their high theoretical energy density, high specific capacity, high safety, and adaptability to uneven surfaces like human body. In the research field of flexible ZABs, a steady progress has been observed, and various ZAB preparation methods have been recently proposed. In this review, the main achievements and limitations of the recent research related to flexible ZABs are described. Firstly, the importance and applications of ZABs are discussed, followed by the working principle and configuration of typical ZABs. In the main text, the recent development of gel electrolytes, anodes, and cathodes is reviewed in detail. Currently, one of the most important limitations in the preparation of high-performance ZABs is the selection or preparation of a suitable gel electrolyte. A good gel electrolyte should have the ability of high-water holding capacity, high and low temperature resistance, high CO₂-tolerance, excellent ionic conductivity, and good mechanical ductility. Several gel electrolytes with various functions have been developed. However, novel gel electrolytes with multifunctional properties have not been developed. In addition, interfaces between the gel electrolyte and air cathode and those between the gel electrolyte and metal anode must be investigated in detail for ZAB performance improvement. Till now, only the effects of physical compression on the electrolyte-air cathode and electrolyte-metal anode interfaces have been adopted and investigated. Moreover, the air cathode and metal anode must exhibit high flexibility to expand the application scope of ZABs as flexible power supplies. Carbon cloth has been typically used as the substrate of the air cathode; however, carbon corrosion occurs under high potential, which needs to be overcome. Meanwhile, the use of nickel mesh or copper foam as the substrate for the cathode will make the flexible ZABs too rigid and not bendable. For the metal anode, mostly zinc sheet or zinc spring have been used to meet the demand of flexibility. However, if novel strategies for the development of doped zinc anodes are investigated, such as those based on the utilization of zinc powder-metal combination, ZAB performance will be significantly improved. If the above-mentioned limitations are overcome, flexible ZABs will not be limited to laboratory use, and can be widely applied in commercial wearable electronic products. Furthermore, the challenges and future perspectives of ZABs are discussed in this review.

Graphitic carbon nitride (g-C₃N₄) has been widely used as a potential photocatalytic material for the removal of tetracycline from water. However, the poor visible light absorption ability and high recombination rate of the photogenerated charge significantly inhibit the catalytic activity of g-C₃N₄. Therefore, facile methods to improve the photocatalytic efficiency of g-C₃N₄ need to be developed. Hematite (α-Fe₂O₃), which has a good visible light absorption and corrosion resistance, is often used for photocatalysis and photo-Fenton reactions. Therefore, a two-dimension/two-dimension (2D/2D) S-scheme heterojunction constructed of g-C₃N₄ and α-Fe₂O₃ nanosheets could be expected to improve the degradation efficiency of tetracycline. In this study, 2D/2D S-scheme α-Fe₂O₃/g-C₃N₄ photo-Fenton catalysts were prepared using a hydrothermal strategy. The photo-Fenton catalytic activity of α-Fe₂O₃/g-C₃N₄ (α-Fe₂O₃ 50% (w)) was significantly improved by the addition of a small amount of H₂O₂, removing 78% of tetracycline within 20 min, which was approximately 3.5 and 5.8 times the removal achieved using α-Fe₂O₃ and g-C₃N₄, respectively. The high catalytic activity was attributed to the synergy between the photocatalysis and Fenton reaction promoted by the continuous Fe³⁺/Fe²⁺ conversion over the 2D/2D S-scheme heterojunction. The 2D/2D S-scheme heterojunction was crucial in the fabrication of the α-Fe₂O₃/g-C₃N₄ photocatalyst with a large surface area, adequate active sites, and strong oxidation-reduction capability. Furthermore, the photo-Fenton reaction provided additional hydroxyl radicals for the degradation of tetracycline with the aid of H₂O₂. The excess reaction product (Fe³⁺) was reduced to Fe²⁺ by the photogenerated electrons from the conduction band of α-Fe₂O₃. The resulting Fe²⁺ could participate in the photo-Fenton reaction. The morphological structures of α-Fe₂O₃/g-C₃N₄ were analyzed using transmission electron microscopy to demonstrate the formation of a 2D/2D structure with face-to-face contact, and the optical properties of the composites were measured using ultraviolet-visible diffuse reflectance spectroscopy. α-Fe₂O₃/g-C₃N₄ possessed a significantly improved visible light absorption compared to g-C₃N₄. Five sequential cyclic degradation tests and X-ray diffraction (XRD) patterns obtained before and after the reaction showed that the α-Fe₂O₃/g-C₃N₄ composites possessed stable photo-Fenton catalytic activity and crystal structures. Transient photocurrent responses of α-Fe₂O₃/g-C₃N₄ demonstrated that the prepared composites exhibited a higher charge transfer efficiency compared to that of single α-Fe₂O₃ and g-C₃N₄. In addition, according to the photoluminescence analysis and active species trapping experiments, a possible S-scheme heterojunction charge transfer process in the photo-Fenton catalytic reaction was proposed. This study provided a promising method for the construction of a high-performance photo-Fenton catalytic system to remove antibiotics from wastewater.

Photocatalytic H₂O₂ production is a sustainable and inexpensive process that requires water and gaseous O₂ as raw materials and sunlight as the energy source. However, the slow kinetics of current photocatalysts limits its practical application. ZnO is commonly used as a photocatalytic material in the solar-to-chemical conversion, owing to its high electron mobility, nontoxicity, and relatively low cost. The adsorption capacity of H₂O₂ on the ZnO surface is low, which leads to the continuous production of H₂O₂. However, its photoresponse is limited to the ultraviolet (UV) region due to its wide bandgap (3.2 eV). Polydopamine (PDA) has emerged as an effective surface functionalization material in the field of photocatalysis due to its abundant functional groups. PDA can be strongly anchored onto the surface of a semiconducting photocatalyst through covalent and noncovalent bonds. The superior properties of PDA served as a motivation for this study. Herein, we prepare an inverse opal-structured porous PDA-modified ZnO (ZnO@PDA) photocatalyst by in situ self-polymerization of dopamine hydrochloride. The crystal structure, morphology, valency, stability, and energy band structure of photocatalysts are characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), electrochemical impedance spectroscopy (EIS), Mott-Schottky curve (MS), and electron paramagnetic resonance (EPR). The experimental results showed that electrons in PDA are transferred to ZnO upon contact, which results in an electric field at their interface in the direction from PDA to ZnO. The photoexcited electrons in the ZnO conduction bands flow into PDA, driven by the electric field and bent bands, and are recombined with the holes of the highest occupied molecular orbital of PDA, thereby exhibiting an S-scheme charge transfer. This unique S-scheme mechanism ensures effective electron/hole separation and preserves the strong redox ability of used photocarriers. In addition, the inverse opal structure of ZnO@PDA promotes light-harvesting due to the supposed "slow photon" effect, as well as Bragg diffraction and scattering. Moreover, the enhanced surface area provides a high adsorption capacity and increased active sites for photocatalytic reactions. Therefore, the resulting ZnO@PDA (0.03% (atomic fraction) PDA) exhibits the optimal H₂O₂ production performance (1011.4 μmol·L^-1·h^-1), which is 4.4 and 8.9 times higher than pristine ZnO and PDA, respectively. The enhanced performance is ascribed to the improved light absorption, efficient charge separation, and strong redox capability of photocarriers in the S-scheme heterojunction. Therefore, this study provides a novel strategy for the design of inorganic/organic S-scheme heterojunctions for efficient photocatalytic H₂O₂ production.

The development of high-performance polymer fibers is one of the main focus areas for the global polymer fiber industry. To ensure the advancement of important industries such as national aerospace, the performance of existing fibers should be improved, while new fibers that combine various properties and functions should also be developed. Carbonene materials, mainly comprising graphene and carbon nanotubes, exhibit excellent mechanical, electrical, thermal, and other properties; thus, they are considered ideal modifiers for high-performance polymer fibers. Herein, carbonene materials modified high-performance polymer fibers are reviewed to provide a comprehensive overview of their preparation, properties, and applications. Firstly, the preparation methods for these fibers, such as the dispersion of carbonene materials and polymer fiber modification methods, will be discussed. The dispersion methods employed for carbonene materials include mechanical mixing as well as covalent and non-covalent functionalization. Although mechanical mixing is relatively straightforward, functionalization typically provides better dispersion. To obtain well-dispersed carbonene materials, these methods should be combined. Polymer fiber modification methods include mixing, in situ polymerization, and coating. Although mixing can be performed during compounding of carbonene materials as well as a wide range of polymers, in situ polymerization generates stronger connections between carbonene materials and polymers, thus resulting in better properties compared to that obtained from mixing. Employing coating as a modification method offers the advantage of improving the surface properties as well as the possibility to introduce additional functionalities to the high-performance polymer fibers. Therefore, during preparation, the structure and function design of carbonene materials modified high-performance polymer fibers should be considered when the compounding method is selected. Subsequent discussions on the properties associated with these fibers will primarily focus on mechanical, electrical, and thermal properties. As carbonene materials can support loads and promote polymer crystallization and molecular chain orientation, it will contribute to improved mechanical properties. In addition, carbonene materials can develop conductive paths in the polymer fiber, thereby improving the electrical properties. These conductive networks further contribute to reducing segment motions in polymer molecular chains at a high temperature, thereby improving the thermal conductivity and thermostability of the materials. Through the addition of carbonene materials, new functions, such as UV resistance, resistance to photo-degradation, and improved surface affinity, can also be introduced. Finally, applications of carbonene materials modified high-performance polymer fibers will be addressed. These include potential applications as structural, heat-resistant, and wear-resistant materials that can be expected to exhibit superior performance when compared to conventional high-performance polymer fibers. Furthermore, additional functions that can be introduced to these modified fibers should make them ideally suited for applications in supercapacitors, sensors, electromagnetic shields, and artificial muscles. To conclude, existing challenges and potential future developments in carbonene materials modified high-performance polymer fibers will be discussed. The excellent properties associated with the modified fibers, as well as continuous development of materials and techniques should ensure their future applications in numerous fields.

Because of the advantages of high safety, environment-friendliness, affordability, and ease of processing, aqueous rechargeable zinc batteries (ARZBs) are promising candidates for next-generation large-scale energy storage systems. In recent years, various cathode materials based on vanadium/manganese/cobalt oxides, Prussian blue analogs, and organic compounds have been reported. Among them, manganese dioxide (MnO₂) is widely used in ARZBs due to their outstanding advantages of low toxicity, eco-friendliness, and high capacity (616 mAh∙g⁻¹ based on two-electron transfer). However, the diversity of the crystal structures of MnO₂ and the unpredictability of the electrochemical reaction make it difficult to investigate the specific internal storage mechanism, which impedes further development of the optimal modification strategies. To date, the main recognized energy storage mechanisms are (de)intercalation and dissolution-deposition mechanisms. In the traditional (de)intercalation mechanism, the predominant issues related to MnO₂ during the cycling process include Mn dissolution, irreversible phase transformation, structural collapse, and sluggish ion diffusion kinetics. On the other hand, the detailed reaction path for the dissolution-deposition mechanism, which was developed in recent years, remains controversial. In addition, the incomplete dissolution-deposition of MnO₂ and the highly acidic environment inevitably leads to corrosion and hydrogen evolution of the zinc anode, as well as low Coulombic efficiency. Accordingly, optimization strategies for different reaction mechanisms have been proposed to make zinc-manganese batteries more competitive. For the (de)intercalation mechanism, modification of composite materials and nanostructure optimization strategies can be adopted to inhibit the dissolution of MnO₂ and increase the number of highly active reaction sites, thus enhancing the electrochemical performance. Moreover, the guest pre-intercalation strategy can help optimize the crystal structure of MnO₂, preventing the collapse of the internal structure during cycling. Besides, defect engineering and element doping strategies focus on regulating the distribution of the electronic structure for affecting the properties of MnO₂, resulting in lowering the energy barrier of zinc insertion. For the dissolution-deposition mechanism, the introduction of a neutral acetate and a halide mediator can effectively facilitate the dissolution-deposition of MnO₂. Meanwhile, metal element catalysis can accelerate the reaction kinetics of the MnO₂ dissolution-deposition, so that high-rate performance can be achieved. Furthermore, the decoupling battery system can separate the cathodic and anodic electrolytes to restrain the hydrogen and oxygen evolution reactions and enhance the potential difference. The flow battery system can effectively eliminate the influence of concentration polarization and stabilize the ion concentration in the electrolytes, thus leading to a large capacity (> 100 mAh). Undoubtedly, MnO₂ as a high-capacity, high-voltage cathode material has broad development prospects for ARZBs. Here, we systematically summarize the crystal structures and reaction mechanisms of MnO₂. We also discuss the optimization strategies toward advanced MnO₂ cathode materials for resolving the highlighted issues in zinc-manganese batteries, which are expected to provide research directions for the design and development of high-performance ARZBs.

In previous decades, lithium-ion batteries (LIBs) were the most commonly used energy storage systems for powering portable electronic devices because LIBs exhibit reliable cyclability. However, owing to the low specific capacity of graphite used in the anode, further increase in the energy density of LIBs was limited. The Li metal anode is promising for the construction of next-generation high-energy-density batteries because of its ultrahigh theoretical capacity (3860 mAh·g^-1) and low redox potential (-3.04 V vs. standard hydrogen electrode). However, the high activity of Li causes dendritic growth during cycling, which leads to cracking of the solid-electrolyte interphase (SEI), increase in side reactions, and formation of dead Li. Several strategies have been proposed to address these issues, including use of electrolyte additives, high-concentration electrolytes, protection of the Li metal surface with various coatings, use of solid-state electrolytes, and design of a three-dimensional (3D) "Li host" for regulating the nucleation and deposition of Li metal. Among them, the design of a 3D "Li host" has proven to be a simple and effective strategy. However, the commonly used 3D "Li hosts" include nanostructured carbons, which are lithiophobic and, thus, provide limited interaction sites with Li⁺ ions, leading to the deposition of Li metal on the "Li host" surface. Therefore, it is necessary to design a 3D "Li host" with enhanced interaction with Li⁺ ions to achieve uniform deposition. Herein, we develop a soft-hard templating route to synthesize 3D macro-/mesoporous C-TiC (denoted as 3DMM C-TiC) nanocomposites, which has been used in Li metal batteries. The as-synthesized materials possess high surface areas (~510 m²·g^-1), ordered structures, large pore volumes, and excellent conductivity. The continuous plating and stripping of Li metal and the formation of the hierarchically porous structure with sufficient volume to allow uniform Li deposition result in the alleviation of the volume change. The high specific surface area significantly decreases the local current density and suppresses dendrite growth. Consequently, ultrasmall TiC nanoparticles are uniformly distributed in the 3D macro-/mesoporous framework, which improves conductivity, enhances their interaction with Li⁺ ions, and promotes the uniform deposition of Li metal. Therefore, the fabricated 3DMM C-TiC||Li battery displays stable cycling performance with improved Coulombic efficiency (98%) over 300 cycles. Moreover, when the 3DMM C-TiC based Li metal anode is assembled with a LiFePO₄ (LFP) cathode, the resultant full cells exhibit high specific capacity and excellent cycling stability. This study provides insight for the effective design of a 3D "Li host" for dendrite-free Li metal anodes.

In the past decade, lithium-sulfur batteries have attracted increasing attention owing to their high energy density and are considered to be one of the key options for the next generation of commercial high energy density batteries. However, for a practical battery system, both high energy density and good safety are important. The safety shortcomings of lithium-sulfur batteries have hindered their development and commercial application. Overcharging is a common battery safety problem. In the case of lithium-sulfur batteries, overcharging triggers the rapid growth of lithium dendrites, which can break through the separator and cause internal short-circuiting, leading to dangerous accidents such as thermal runaway and explosions. In practice, an electronic control device is typically installed in a battery to monitor its charging voltage and avoid overcharging avoid overcharging. However, this method increases the cost, weight, and size of the battery system, and reduces the energy density. For the self-protection of lithium-sulfur batteries in the case of overcharging, many polymerizable aromatic compounds are used as additives to improve the overcharge tolerance of lithium batteries. When the electrode surface is covered by a polymer film formed by employing electropolymerization, the cell dies permanently; thus the overcharge protection works only once. In contrast, electroactive polymers having reversible electrochemical doping/dedoping properties can be used to inhibit the overcharging of lithium-sulfur batteries is a more attractive approach. In this study, voltage-sensitive polytriphenylamine (PTPAn) was prepared by the chemical oxidation of triphenylamine as a raw material and successfully applied to lithium-sulfur battery separator. The conductivity test results showed that the PTPAn/polypropylene (PP) separator has an ionic conductivity of 1.56 mS·cm^-1. The cyclic voltammogram (CV) test results showed that the PTPAn/PP separator has a redox peak in the range of 3.5?.2 V. At a charge/discharge rate of 0.1C, the lithium-sulfur batteries with the PTPAn/PP separator and blank PP separator had a discharge specific capacity of 424.8 and 407.2 mAh·g^-1, respectively after 200 cycles, with Coulombic efficiencies of 99.38% and 98.59%, respectively. Further, the rate (0.1C, 0.2C, 0.5C, 1C) tests showed that the lithium-sulfur batteries with PTPAn/PP separator had higher discharge specific capacities at different rates than the lithium-sulfur batteries with the blank PP separator. Moreover, when the lithium-sulfur battery with the PTPAn/PP separator was overcharged at the 4th cycle, the charge specific capacity was 843.1 mAh·g^-1 and the discharge specific capacity was 839.8 mAh·g^-1. The charging specific capacity was 690.2 mAh·g^-1 and the discharging specific capacity was 669.2 mAh·g^-1 at the 10th cycle of overcharging. At the 16th cycle of overcharging, the battery had a charge specific capacity of 538.7 mAh·g^-1 and a discharge specific capacity of 512.9 mAh·g^-1. The overcharge test showed that lithium-sulfur batteries with the PTPAn/PP separator continued to work well after different overcharge rates. At an overcharging rate of 1C, the battery voltage remained stable at 3.9 V, with a charge specific capacity of 349.8 mAh·g^-1 and a discharge specific capacity of 328.7 mAh·g^-1.

Throughout the twentieth century, temperatures climbed rapidly as the use of fossil fuels proliferated and greenhouse gas levels soared. Thus, the need to develop environmentally friendly energy sources to replace traditional fossil fuels is urgent. Clean and highly efficient, hydrogen is considered the most promising energy source to replace traditional fossil fuels. The production of hydrogen by photocatalytic water splitting is environmentally friendly, and is considered the most promising method for producing hydrogen energy. Enhancing the separation efficiency of photogenerated electron-hole pairs has been identified as a key milestone for constructing high-efficiency photocatalysts. However, the construction of efficient and stable hydrogen-evolution photocatalysts with highly dispersed cocatalysts remains a challenge. Here, we succeeded, for the first time, in fabricating P-doped CNS (PCNS) with a highly dispersed non-noble trimetallic transition metal phosphide Co_0.2Ni_1.6Fe_0.2P cocatalyst (PCNS-CoNiFeP), by a one-step in situ high-temperature phosphating method. Remarkably, the CoNiFeP in PCNS-CoNiFeP demonstrated no aggregation and high dispersibility compared with CoNiFeP prepared by the traditional hydroxide-precursor phosphating method (PCNS-CoNiFeP-OH). X-ray diffraction, X-ray photoelectron spectroscopy, element mapping images, and high-resolution transmission electron microscopy results demonstrate that PCNS-CoNiFeP was successfully synthesized. The UV-Vis absorption results indicate a slight increase in absorbance for PCNS-CoNiFeP in the 200–800 nm wavelength region compared with that of PCNS. Photoluminescence spectroscopy, electrochemical impedance spectroscopy, and photocurrent results demonstrated that CoNiFeP cocatalysts could effectively promote the separation of photogenerated electron-hole pairs and accelerate the migration of carriers. The linear sweep voltammetry results also demonstrate that the CoNiFeP cocatalyst loading could significantly decrease the overpotential of CNS. Therefore, the maximum hydrogen evolution rate of PCNS-CoNiFeP was 1200 μmol·h^-1·g^-1, which was approximately four times higher than that of pure CNS-Pt (320 μmol·h^-1·g^-1) when using TEOA solution as a sacrificial agent. The apparent quantum efficiency of PCNS-CoNiFeP was 1.4% at 420 nm. The PCNS-CoNiFeP also exhibited good stability during the photocatalytic reaction. In addition, the TEM results indicate that CoNiFeP with a size of 6–8 nm are highly dispersed on the PCNS surface. The highly dispersed CoNiFeP demonstrated better charge-separation capacity and higher intrinsic electrocatalytic hydrogen-evolution activity than the aggregated CoNiFeP. Thus, the hydrogen evolution rate of aggregated CoNiFeP-PCNs (300 μmol·h^-1·g^-1) was much lower than that of PCNS-CoNiFeP. Furthermore, P doping of CNS could improve electric conductivity and charge transport. It is expected that loading highly dispersed CoNiFeP and P doping could be extended to promote photocatalytic hydrogen production using various photocatalysts.

Bifunctional electrocatalysts in alkaline media play an important role in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), owing to the considerable influence of water splitting in the green energy sector. Herein, we present surface-modified NiCo₂O₄ nanowires (NWs) with rich defects as a highly efficient overall water splitting electrocatalyst in alkaline media, where the surface modification is accomplished using organic ligands. X-ray photoelectron spectroscopy reveals that the increase in the Co²⁺/Co³⁺ ratio is responsible for the excellent bifunctional electrocatalytic performance of the surface-modified NiCo₂O₄ NWs. As expected, benefiting from the organic ligand-dominated surface modification, the optimized NiCo₂O₄ NWs can display an overpotential of only 83 mV for the HER and 280 mV for the OER, with a current density of 10 mA·cm^-2 in 1.0 mol·L^-1 KOH solution. More importantly, the NiCo₂O₄ NWs surface-modified using organic ligands exhibit outstanding performance for overall water splitting, with a voltage of 2.1 V and current density of 100 mA·cm^-2, and also maintain their activity for at least 15 h. The present work highlights the importance of increasing the content of Co²⁺ in the spinel structure of NiCo₂O₄ NWs for enhancing their performance in overall water splitting.

Constructing an efficient and stable heterojunction photocatalyst system is a promising approach to achieve solar-driven water splitting to produce hydrogen. In this work, a novel Mn_0.2Cd_0.8S@CoAl LDH (MCCA) S-scheme heterojunction was successfully prepared through the efficient coupling of Mn_0.2Cd_0.8S nanorods and CoAl LDH nanosheets, employing a physical mixing method. The photoluminescence and photocurrent-time response results demonstrated that the internal electric field of the constructed MCCA S-scheme heterojunction could successfully accelerate charge separation and electron transfer between the Mn_0.2Cd_0.8S interface and the CoAl LDH. Critically, the introduction of the CoAl LDH effectively inhibited the recombination of photogenerated electrons and holes, thereby improving the photocatalytic hydrogen production activity of Mn_0.2Cd_0.8S. A maximum H₂ production of 1177.9 μmol in 5 h was obtained with MCCA-3. This represents a significant improvement compared to what can be achieved with the pure Mn_0.2Cd_0.8S nanorods and CoAl LDH nanosheets individually. This work provides a simple and effective approach for the rational design of S-scheme heterojunction photocatalysts for photocatalytic hydrogen production.

With rapid industrialization, issues pertaining to the environment and energy have become an alarming concern. Photocatalytic water splitting is considered one of the most promising green technologies capable of resolving these issues, as it can convert solar energy into chemical energy and have a positive impact on the realization of "carbon neutrality". Current research focuses on the development of highly efficient catalysts to improve the photocatalytic H₂-production activity. Transition metal phosphides and sulfides are often used as photocatalysts owing to their low H₂-evolution overpotential and excellent electrical conductivity. Among them, Ni₂P and NiS have generally been used independently during photocatalytic H₂ production; however, it is necessary to study the synergistic effect when they are combined as a dual cocatalyst. In this work, we successfully prepared a Ni₂P-NiS dual cocatalyst for the first time via a simple hydrothermal method using red phosphorus (RP) and thioacetamide (C₂H₅NS) as the sources of P and S. Ni₂P-NiS was then introduced to the surface of g-C₃N₄ nanosheets through solvent evaporation to create a Ni₂P-NiS/g-C₃N₄ heterojunction. Furthermore, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet-visible spectrophotometry (UV-Vis), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), linear sweep voltammetry (LSV), Mott-Schottky (M-S), and electrochemical impedance spectroscopy (EIS) were used to reveal the crystal structures, morphologies, element compositions, and photoelectric characteristics of the samples; thus, it was demonstrated that Ni₂P-NiS was successfully deposited on the surface of g-C₃N₄ and that together they exhibited better activity than their monomers. Moreover, the optimized 15% Ni₂P-NiS/g-C₃N₄ composite exhibits a H₂ generation rate of 6892.7 μmol·g^-1·h^-1, which is about 46.1, 7.5 and 4.4 times higher than that of g-C₃N₄ (150 μmol·g^-1·h^-1), 15% NiS/g-C₃N₄ (914.5 μmol·g^-1·h^-1), and 15% Ni₂P/g-C₃N₄ (1565.9 μmol·g^-1·h^-1), respectively. In addition, photoelectric performance tests show that Ni₂P-NiS/g-C₃N₄ has a stronger photocurrent intensity, smaller charge-transfer resistance, more positive H₂-evolution overpotential, and better charge-separation ability than the individual components (i.e., Ni₂P and NiS), suggesting that the coexistence of Ni₂P and NiS can further boost the activity of g-C₃N₄ during H₂ evolution compared with their monomers. This is mainly due to the Schottky barrier effect between Ni₂P-NiS nanoparticles and g-C₃N₄ nanosheets, which can greatly promote charge separation and charge transfer at their interface. Additionally, Ni₂P-NiS can reduce the H₂-evolution overpotential, leading to the increased surface kinetics of H₂ evolution. This work offers a promising approach to obtaining a highly active and stable noble-metal-free dual cocatalyst for photocatalytic H₂ production.

The storage and conversion of renewable energy through electrocatalysis is of considerable significance for improving the energy structure, protecting the ecological environment, and achieving the national strategy of carbon peaking and carbon neutrality. The development of low-cost and high-efficiency electrocatalysts has become a major scientific challenge worldwide. Microorganisms are widely found in nature and are characterized by their rich structure, composition and metabolism. These properties facilitate their use as intelligent templates for electrocatalyst structures and as sources of non-metallic elements such as carbon, phosphorus, sulfur, as well as metallic elements. The use of microorganisms in electrocatalyst production has become a new trend owing to the advantages of non-toxicity, reproducible production, and ease of scaling up. Thus, this paper reviews the development of microbial "intelligence" guided preparation of electrocatalysts and their current applications in the fields of hydrogen evolution reactions, oxygen evolution reactions, oxygen reduction reactions, carbon dioxide reductions and lithium batteries. In order to achieve the function of "intelligent" guidance of microorganisms, four aspects need to be addressed: (1) the selection of suitable microbial species and the culture and activation conditions, which significantly helps in tailoring the microbial properties for specific applications; (2) the exploration of microbial species that can accumulate metal species from their living environment and thus produce metal nanoparticles, which will help obtain nanocomposites with desired properties; (3) the selection of compounds with good catalytic properties, high stability, and compatibility with microbial substrates; and (4) the development of highly controllable nanocatalysts through modern molecular biology and genetic engineering to regulate microbial life processes such as metabolic proliferation and apoptosis. With the resolution of these issues, we believe that the application of microbial intelligent templates guided electrocatalysts can be further extended to other electrocatalytic reactions such as ethanol oxidation reactions (EOR), nitrogen reduction reactions (NRR), and to other applications in fields such as electronics, sensing, imaging, and biomedicine. The goal of this review is to promote a deeper understanding of the correlations among microbial metabolism, catalyst micro-nano structures and structure-activity relationships. Furthermore, the challenges associated with such materials and the prospects for future development are discussed herein.

Catalytic reduction of CO₂ to CO has been considered promising for converting the greenhouse gas into chemical intermediates. Compared to other catalytic methods, photocatalytic CO₂ reduction, which uses solar energy as the energy input, has attracted significant attention because it is a clean and inexhaustible resource. Therefore, using high-performance photocatalysts for effective CO₂ reduction under mild reaction conditions is an active research hotspot. However, several current photocatalysts suffer from low solar energy conversion efficiency due to the extensive charge recombination and few active sites, leading to low CO₂ reduction efficiency. Generally, constructing an S-scheme heterojunction can not only promote charge separation but also help maintain strong redox ability. Therefore, the S-scheme heterojunction is expected to help in achieving high conversion activity and CO₂ reduction efficiency. Here, 2D tetragonal BiOBr_0.5Cl_0.5 nanosheets and hexagonal WO₃ nanorods were prepared using a simple hydrothermal synthesis method, and the 2D/1D BiOBr_0.5Cl_0.5 nanosheets/WO₃ nanorods (BiOBr_0.5Cl_0.5/WO₃) S-scheme heterojunction with near infrared (NIR) light (> 780 nm) response were prepared via the electrostatic self-assembly method for the photocatalytic CO₂ reduction. Following characterization and analysis, including diffuse reflectance spectra (DRS), Mott-Schottky plots, transient photocurrent response, time-resolution photoluminescence spectrum (TRPL), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and electron spin resonance (ESR) measurements, it can be demonstrated that an S-scheme carrier transfer route was formed between the 2D BiOBr_0.5Cl_0.5 nanosheets and 1D WO₃ nanorods. Driven by the internal electric field, which was formed between the two semiconductors, electron migration was boosted, thus inhibiting the recombination of photogenerated carriers, while the stronger redox ability was maintained, thus providing good reduction efficiency over BiOBr_0.5Cl_0.5/WO₃ composite in CO₂ reduction. In addition, the 2D/1D nanosheet/nanorod structure allowed for enhanced interface contact with abundant active sites, which favored charge separation and increased photocatalytic activity. Furthermore, the amount of WO₃ nanorods added during the preparation of the composites was altered, which led to the optimal amount of 5% (w, mass fraction) for the photocatalytic CO₂ reduction. As a result, the BiOBr_0.5Cl_0.5/WO₃ composite exhibited superior photocatalytic reduction performance with a CO yield of 16.68 μmol·g^-1·h^-1 in the presence of any precious metal cocatalyst or sacrificial agent, which was 1.7 and 9.8 times that of pure BiOBr_0.5Cl_0.5 and WO₃, respectively. In addition, the BiOBr_0.5Cl_0.5/WO₃ composite provided continuously increased CO yields with excellent selectivity under full-spectrum light irradiation, suggesting good photocatalytic stability. This work describes a novel idea for the construction of 2D/1D S-scheme heterojunction photocatalysts for efficient CO₂ reduction.

With the rapid development of industrial technology, a large number of organic pollutants are routinely released into the environment, which has caused serious problems. Semiconductor photocatalysis is an environmentally-friendly and effective method to degrade and remove typical pollutants, and photocatalysts play a key role in the application of this technology. Therefore, various semiconductor materials have been tried and used in the field of pollutant removal. Graphite carbon nitride (g-C₃N₄) has attracted great interest because of its two-dimensional layered structure and good visible light response range. Owing to a narrow bandgap, adjustable band structure, and high physicochemical stability, g-C₃N₄ absorbs wavelengths up to 450 nm in the visible spectrum, leading to an opportunity for visible-light photocatalytic performance. Nevertheless, there are still some drawbacks that limit the photocatalytic efficiency of g-C₃N₄ in the removal of antibiotics and dyes under visible light, such as the rapid recombination of photoinduced charges and the weak oxidation capacity of holes. To advance this promising photocatalytic material, multiple methods have been tried to optimize the electronic band structure of g-C₃N₄, such as doping with various elements, morphology control, and functional group modification. Recently, a novel type of Step-scheme (S-scheme) heterojunction composed of two n-type semiconductor photocatalysts has been proposed, which can utilize a more positive valance band and a more negative conduction band. It was demonstrated that the formation of S-scheme heterojunctions is a valid way to increase photocatalytic activity of g-C₃N₄. Herein, novel 0D/2D Bi₄V₂O₁₁/g-C₃N₄ S-scheme heterojunctions were prepared by a simple in situ solvothermal growth method. The Bi₄V₂O₁₁/g-C₃N₄ composites displayed a high photocatalytic activity through the removal of oxytetracycline (OTC) and Reactive Red 2. In particular, the BVCN-50 composite showed the highest degradation efficiency for OTC of 74.1% and for Reactive Red 2 of 84.2% with ·O₂^- as the primary active species. This highly improved photocatalytic performance can be ascribed to the generation of S-scheme heterojunctions, which provides for a high redox capacity of the heterojunction system (strong oxidative ability of Bi₄V₂O₁₁ and strong reductive capacity of g-C₃N₄) and facilitates the space separation of photo-generated charges. Moreover, the surface plasmon resonance effect of metallic Bi⁰ broadens the light utilization range of the heterojunction system. In addition, the possible degradation pathway and intermediates throughout the degradation process of OTC based on liquid chromatograph mass spectrometer (LC-MS) analysis were also studied. This work provides a novel tactic for the design and fabrication of g-C₃N₄-based S-scheme heterojunctions with enhanced photocatalytic performance.

Sustainable fuels and chemicals are receiving unprecedented attention worldwide in the context of achieving global carbon neutrality. Biomass, as the only natural and sustainable carbon-based source, shows great potential in addressing our current environmental/energy problems and in creating a carbon-neutral society. Lignocellulosic biomass is made up of basic structural units containing C―O/C―C bonds, and the catalytic cleavage of these C―O/C―C bonds is the key for biomass valorization; thus, garnering considerable attention in the past decade. This viewpoint begins with a brief report on the current status of catalytic activation/cleavage of C―O/C―C bonds during biomass conversion, and then goes on to discuss the key challenges experienced and possible strategies that can be implemented using cooperative catalysis. Our goal is not to provide a comprehensive overview of the activation/cleavage of the C―O/C―C bonds in biomass, but rather to highlight the core questions and challenges related to this process and the requirements for future investigations. We selected several representative C―O/C―C bonds in carbohydrates and lignin to discuss their catalytic mechanism in terms of total/selective bond cleavage, and then present our own insights for future studies. Therefore, this article mainly discusses the following two aspects: (1) The activation and cleavage of C―O bonds, which includes total and selective C―O bond cleavage in furan-based fuel precursors and lignin. When aiming to produce liquid fuels, including alkanes and arenes from biomass, the total cleavage of C―O bonds is essential. During the hydrodeoxygenation (HDO) of furan-based fuel precursors, various C―O bonds need to be cleaved, especially the C―O bond of each tetrahydrofuran ring, which has the highest bond energy. When compared with the total HDO of fuel precursors, the removal of the phenolic hydroxyl groups in lignin to produce arenes is more challenging because of the competition between the over-hydrogenation of the benzene rings and the cleavage of phenolic C―O bonds. The selective or partial cleavage of C―O/C―C bonds to form highly functionalized chemicals has recently attracted great interest and is believed to be a dynamic future research avenue. For example, the production of phenol from lignin or lignin-model compounds, through the selective removal of methoxy groups and para-side-chain groups, while preserving the phenolic hydroxyl groups, has been extensively explored in the past few years. (2) The other important aspect of this article is the cleavage of the C―C bonds in carbohydrates and lignin. The cleavage of carbohydrate C―C bonds occurs via retro-aldol condensation, which produces propylene glycol, ethylene glycol, ethanol, and lactic acid. The cleavage of C―C bonds in lignin is challenging because the bond energy of the C―C bonds is generally higher than that of the C―O bonds in lignin. Therefore, in this section, we discuss the cleavage of the strongest 5―5' bond in lignin. Finally, some subjective perspectives and future directions are provided, also highlighting several major challenges in this field.

Industrialization undoubtedly boosts economic development and improves the standard of living; however, it also leads to some serious problems, including the energy crisis, environmental pollution, and global warming. These problems are associated with or caused by the high carbon dioxide (CO₂) and sulfur dioxide (SO₂) emissions from the burning of fossil fuels such as coal, oil, and gas. Photocatalysis is considered one of the most promising technologies for eliminating these problems because of the possibility of converting CO₂ into hydrocarbon fuels and other valuable chemicals using solar energy, hydrogen (H₂) production from water (H₂O) electrolysis, and degradation of pollutants. Among the various photocatalysts, silicon carbide (SiC) has great potential in the fields of photocatalysis, photoelectrocatalysis, and electrocatalysis because of its good electrical properties and photoelectrochemistry. This review is divided into six sections: introduction, fundamentals of nanostructured SiC, synthesis methods for obtaining nanostructured SiC photocatalysts, strategies for improving the activity of nanostructured SiC photocatalysts, applications of nanostructured SiC photocatalysts, and conclusions and prospects. The fundamentals of nanostructured SiC include its physicochemical characteristics. It possesses a range of unique physical properties, such as extreme hardness, high mechanical stability at high temperatures, a low thermal expansion coefficient, wide bandgap, and superior thermal conductivity. It also possesses exceptional chemical characteristics, such as high oxidation and corrosion resistance. The synthesis methods for obtaining nanostructured SiC have been systematically summarized as follows: Template growth, sol-gel, organic precursor pyrolysis, solvothermal synthesis, arc discharge, carbon thermal reduction, and electrospinning. These synthesis methods require high temperatures, and the reaction mechanism involves SiC formation via the reaction between carbon and silicon oxide. In the section of the review involving the strategies for improving the activity of nanostructured SiC photocatalysts, seven strategies are discussed, viz., element doping, construction of Z-scheme (or S-scheme) systems, supported co-catalysts, visible photosensitization, construction of semiconductor heterojunctions, supported carbon materials, and construction of nanostructures. All of these strategies, except element doping and visible photosensitization, concentrate on enhancing the separation of holes and electrons, while suppressing their recombination, thus improving the photocatalytic performance of the nanostructured SiC photocatalysts. Regarding the element doping and visible photosensitization strategies, element doping can narrow the bandgap of SiC, which generates more holes and electrons to improve photocatalytic activity. On the other hand, the principle of visible photosensitization is that photo-induced electrons move from photosensitizers to the conduction band of SiC to participate in the reaction, thus enhancing the photocatalytic performance. In the section on the applications of nanostructured SiC, photocatalytic H₂ production, pollutant degradation, CO₂ reduction, photoelectrocatalytic, and electrocatalytic applications will be discussed. The mechanism of a photocatalytic reaction requires the SiC photocatalyst to produce photo-induced electrons and holes during irradiation, which participate in the photocatalytic reaction. For example, photo-induced electrons can transform protons into H₂, as well as CO₂ into methane, methanol, or formic acid. Furthermore, photo-induced holes can convert organic waste into H₂O and CO₂. For photoelectrocatalytic and electrocatalytic applications, SiC is used as a catalyst under high temperatures and highly acidic or basic environments because of its remarkable physicochemical characteristics, including low thermal expansion, superior thermal conductivity, and high oxidation and corrosion resistance. The last section of the review will reveal the major obstacles impeding the industrial application of nanostructured SiC photocatalysts, such as insufficient visible absorption, slow reaction kinetics, and hard fabrication, as well as provide some ideas on how to overcome these obstacles.

Flexible and wearable electronics can integrate multiple functions, such as sensing, actuation, and wireless communication, showing great potential for application in flexible displays, health monitoring, human-computer interaction, and other fields. Energy devices to supply power are an important part of wearable electronics. Traditional energy devices have a relatively rigid plate structure, and their poor mechanical flexibility, low breathability and moisture conductivity make them difficult to adapt to the needs of wearability. These problems have severely limited the development and application of wearable devices, and there is therefore an urgent need to develop flexible, lightweight, high-performance wearable energy devices. Fiber-based energy devices have several obvious advantages. First, the diameter of these devices usually ranges from micrometers to millimeters, which makes them small in size and light in weight. Then, their outstanding flexibility endows them with wearable comfort and stable performance under mechanical deformation. Third, fibers can be woven or knitted into deformable textiles with excellent wearability and breathability. Because of these advantages, fiber-based energy devices have attracted considerable attention. Traditional fiber-based energy devices usually use polymer fibers covered by metal wires as electrodes, but these have inherent defects, such as poor chemical stability, inferior matching with active materials, and a lack of mechanical flexibility, that hinder their application in wearable devices. Carbonene materials are low-dimensional all-carbon materials composed of sp²-hybridized carbon atoms, including carbon nanotubes and graphene, which have the advantages of low density, good mechanical properties, excellent electrical and thermal conductivity, and high stability. "Carbonene fibers" mainly refers to high-performance fiber-like macroscopic assemblies composed of carbonene materials, and includes carbon nanotube fibers, graphene fibers, and graphene/carbon nanotube composite fibers. Carbonene fibers can effectively transfer the excellent performance of carbonene materials at the micro scale to the macro scale, showing high conductivity, strength, flexibility, stability, and ease of manufacture, making them widely used in research on advanced energy devices. In recent years, researchers have developed a variety of carbonene fiber-based energy devices. This paper reviews recent progress in the application of carbonene fibers in energy devices, including energy conversion and energy storage devices such as solar cells, moisture actuators and moisture power generators, thermoelectric generators, supercapacitors, and electrochemical cells. The preparation methods and wearable applications of carbonene fiber-based energy devices are emphasized. Discussion of the development prospects and challenges of energy storage/conversion devices based on carbonene fibers is included, and it is expected that this will provide valuable ideas for the future development of high-performance fiber-based wearable energy devices.

Compared to traditional sensor device arrays, optical fiber systems capable of wide-range detection are gradually emerging as strong candidates for distributed monitoring owing to their simplified structure. However, the working mechanism of optical fiber sensors limits their use to the detection of physical parameters such as refractive index and is an obstacle for the detection of small doses of molecules by optical fiber systems. Several researchers have focused on this aspect to endow sensitivity to these optical fibers for gas or liquid molecules. By deliberately destroying the fiber structure, strong interactions between the evanescent field of optical fibers and the target materials, such as microfibers, D-shaped fiber, etc. can be achieved. Assisted by the surface plasmon resonance techniques, such configurations can exhibit highly enhanced sensitivity to a change in the refractive index caused by gas or liquid molecules. Two-dimensional materials are an excellent candidate as coating materials due to their high specific surface area, which also guarantees a large sensing response and simultaneously minimizes any side effects by suppressing the propagating mode of optical fibers. However, owing to the obstacles in optical fiber engineering and device fabrication, the abovementioned functional 2D sensors are still limited to sample-scale fabrication, and their mass-production has not yet been realized. An all-fiber distributed sensing system with high single-spot sensitivity is still difficult to fabricate. Here, we propose a new configuration of a grid-distributed environmental optical fiber sensing by introducing low-pressure chemical vapor deposition (LPCVD)-grown graphene photonic crystal fiber (PCF) into the optical fiber sensing system. We successfully synthesized monolayer and/or bilayer graphene in the air holes of PCF. By fusing the graphene PCF (Gr-PCF) to a single mode optical fiber, we fabricated an all-optical-fiber sensing system. Preliminary experiments suggest that Gr-PCF can selectively detect NO₂ gas at ppb-level and exhibit ionic sensitivity in liquids. The ability to detect NO₂ gas is attributed to the graphene layer's interaction among light-mode and adsorbed molecules: adsorption-induced additional hole-doping caused a shift in the Fermi level of graphene and eventually modulated its light absorption, leading to changes in the light intensity signals. We believe that the sensor can be extended to other kinds of gases and liquids, considering the affinity of graphene toward various molecules. In view of practical optical sensors, our design is compatible with the time domain or wavelength domain multiplexing techniques of optical fiber communication systems. Because CVD-based synthesis can be used to realize mass production, the design proposed herein shall be one of the answers to the distributed optical fiber environmental sensors.