As one of the most promising materials in the field of photovoltaics, organic- inorganic hybrid perovskites have attracted widespread attention in recent years. In addition to their promising applications in the field of photovoltaics, perovskite materials also exhibit outstanding photoluminescence and electroluminescence properties. This paper reviews the latest developments in organic- inorganic hybrid perovskite materials, with particular attention paid to the luminescence. Firstly, a summary of the fundamental issues related to the unique light emitting characteristics and influencing factors of perovskite materials is provided, including the light-emitting mechanism and principles related to spectrum adjustability. The influence of the morphology of perovskite on the photoluminescence properties is discussed. The latest developments and applications of perovskite materials in various devices, including light-emitting diodes, lasers, and lightemitting field effect transistors, are then discussed. Finally, the key issues and challenges of perovskite light emitting materials are addressed and prospects for future perovskite-based applications are discussed.
Graphitic carbon nitride (g-C3N4) is a new metal-free material. Owing to its multiple unique physicochemical properties, g-C3N4 has promising applications in various research fields, including heterogeneous catalysis, photocatalysis, fuel cells, and gas storage. Compared with bulk g-C3N4 prepared via direct thermal condensation, mesoporous g-C3N4 possesses a higher surface area and abundant accessible mesoporous pores. These features expose many more surface active sites, thereby improving the performance of this material in catalysis as well as in other applications. Thermal condensation is the most convenient strategy to prepare g-C3N4 and, when fabricating mesoporous g-C3N4, one may employ hard-, soft-, or non-templating method. This paper reviews recent advances in the synthesis of mesoporous g-C3N4 using all three routes. Specifically, several crucial issues regarding the hard-templating method are discussed with regard to the synthetic mechanism associated with various precursors and the physicochemical properties of the g-C3N4 products. Novel soft- and non-templating approaches for the preparation of mesoporous g-C3N4 are also addressed and a detailed comparison to the hard-templating method is provided. Finally, future prospects for the development of mesoporous g-C3N4 materials are also assessed.
Conversion of carbon dioxide (CO2) to value-added chemicals and fuels driven by low-grade renewable electricity is of significant interest since it serves the dual purpose of reducing atmospheric content of CO2 by utilizing it as a feedstock and storing it in the form of high-energy-density fuels. In this regard, there are an increasing number of interesting developments taking place in the popular research focus area of electrochemical reduction of CO2. This review first introduces the general principles of CO2 electroreduction. Next, the latest progress relating to electrocatalytic materials and experimental and theoretical studies of the reaction mechanism has been discussed. Finally, the challenges and prospects for further development of CO2 electroreduction have been presented.
In recent years, significant breakthroughs have been achieved in the development of organicinorganic halide lead perovskite solar cells, with reported power conversion efficiency (PCE) values of up to 22.1%. This value is comparable to the efficiencies obtained using CdTe (22.1%) and CuInGaSn (CIGS) (22.3%) solar cells, and close to the value associated with crystalline silicon solar cells (approximately 25%). However, the limited long-term output efficiency stability and lead toxicity issues associated with organic-inorgan lead halide perovskite cells have limited their commercial applications. This review focuses on these issues and corresponding solutions for halide lead hybrid perovskite solar cells, and discusses advances and developments in Pb-free inorganic perovskite solar cells. We also examine the current body of knowledge regarding perovskite solar cells and discuss critical points and expectations regarding further performance improvements.
Sodium ion batteries (SIBs) have attracted increasing attention for energy storage systems because of abundant and low cost sodium resources. However, the large ionic radius of sodium and its slow electrochemical kinetics are the main obstacles for the development of suitable electrodes for high-performance SIBs. The development of high-performance cathode materials is the key to improving the energy density of SIBs and facilitating their commercialization. Herein, we review the latest advances and progress of cathode materials for SIBs, including transition metal oxides, polyanions, ferrocyanides, organic materials and polymers, and amorphous materials. Additionally, we have summarized our previous works in this area, explore the relationship between structure and electrochemical performance, and discuss effective ways to improve the reversibility, working potential and structural stability of these cathode materials.
As a new type of energy storage device, supercapacitors with high specific capacitance, fast charge and discharge, and long cycle life have attracted significant attention in the energy storage field. Electrode materials are a crucial factor defining the electrochemical performance of supercapacitors. The standard supercapacitor electrode materials used can be classified into three types:carbon-based materials, metal oxides and hydroxide materials, and conductive polymers. This review introduces the principles of supercapacitors and summarizes recent research progress of carbon-based electrode materials, including pure carbon materials, and the binary and ternary complex materials with carbon.
Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers, constructed with lightweight elements by covalent bonds. Owing to their low density, high thermal stability, and inherent porosity, COFs have many potential applications in gas adsorption, heterogeneous catalysis, energy storage, etc. This article reviews the latest progress in COFs, including their structural design, synthesis, purification, characterization methods, and applications in gas adsorption, catalysis, and photoelectricity. Finally, the prospects of COFs are also discussed.
Graphene aerogels are obtained from graphene sheets through wet chemical assembly or vaporphase chemical growth. They have a three dimensional graphene architecture that has an interconnected network with a high specific surface area, good electric conductivity and other physicochemical properties and thus has important applications in electrochemical energy storage, adsorption, catalysis and sensing. In this review, we will highlight the assembly strategies and structural designs used to introduce the controlled assembly of the graphene sheets in graphene aerogel materials, such as graphene oxide-, reduced graphene oxide-, CVDgrown graphene and composite graphene aerogels. The current challenges and future development of the grapheme aerogels are also discussed.
Lithium ion batteries (LiBs) have been widely utilized, but the limited lithium resource restricts development and application of LiBs in large-scale energy storage. Sodium has similar physicochemical characteristics to that of lithium and is suitable to transfer between two electrodes as a cation in the "rocking chair" mechanism of LiBs. Na-containing compounds have been proposed as the electrodes to store sodium ions and provide channels for diffusion. Polyanion Na3V2(PO4)3 is a Na-super-ionic conductor (NASICON) with specific Na sites in its crystal structure and three-dimensional open channels. Recently, Na3V2(PO4)3 has been demonstrated as potential electrode material with promising properties for energy storage. In this review we systematically summarize the structure of Na3V2(PO4)3, the application and mechanism in a specific energy system, and the recent development of Na3V2(PO4)3 structure for use as electrodes. The potential problems and trends of Na3V2(PO4)3 are also discussed.
Over the past decade, graphene has been the focus of intensive research because of its remarkable physical and chemical properties. Researchers have made many efforts to synthesize graphene and investigate its potential applications. In this article, we first briefly review the fabrication processes and properties of graphene. Then, we discuss the application of graphene/Ag hybrid films as transparent conductive films (TCFs). Next, we introduce our results on this topic. Graphene and Ag nanowires were synthesized by chemical vapor deposition (CVD) and the polyol process, respectively. We successfully fabricated a graphene/Ag hybrid film with a low sheet resistance (Rs) of 26 Ω·□-1. Finally, we describe the main challenges facing graphene hybrid films and their potential applications in a wide range of optoelectronic devices.
Bi-based semiconductor photocatalysts are important visible-light-driven photocatalysts. However, the photocatalytic performance of bulk bismuth-containing compounds remains unsatisfactory. Many investigations indicate that morphology control and surface modification are effective methods for improving the photocatalytic activity of these compounds. Herein, we review recent advances in this field, including ultrathin nanoplate fabrication, facet ratio control, hierarchical and hollow architecture construction, functional group and quantum-sized nanoparticle modification, surface defect regulation, and in situ formation of metal bismuth and bismuth compounds. The characteristics and advantages of these modification methods are introduced. In addition, mechanisms for improving light absorption, separation, and utilization of excited carriers are discussed. Trends in the development of Bi-based photocatalysts using morphology control and surface modification, as well as the challenges involved, are also analyzed and summarized.
Metal organic frameworks (MOFs) have attracted tremendous attention in electrochemical energy storage and conversion because of their large surface area, high porosity, ordered structure and the tailorability of the structure. In this paper, the unique advantages of synthesizing electrocatalysts from MOFs are introduced. Then, the latest research progress of MOFs derived electrocatalysts in electrochemical energy conversion is mainly summarized. Finally, the application prospects, opportunities and challenges of MOF-based materials are briefly presented to provide an outlook for future research directions.
It is the goal of density functional theory (DFT) researchers to develop the functional formalism of exchange-correlation (XC) with high accuracy and efficiency. Conventional functionals have issues when predicting the properties of the ground and excited states of atomic and molecular systems, and they do not show universal predictions. On the other hand, high-level theory methods such as the couple-cluster (CC) method and many-body perturbation theory (MBPT) based on GW (i.e., the dressed Green's function (G) and the dynamically screened Coulomb interaction (W)) approximation require very expensive computational cost and therefore the size of the systems studied and the practicability are limited. Recently, the optimally tuned range-separated (RS) functional has been developed to partly alleviate the above issues and has attracted great attention because it can achieve a level of accuracy comparable to the high-level method but with low computational cost. In this review, we first provide an overview of the theory in this field and then introduce the optimal tuning concept based on the RS functional. We combine the recent theoretical studies to evaluate their performance in practical calculations. Finally, we give some prospects for the future development and application of the optimally tuned approach.
Hydrogen produced from electrochemical water-splitting driven by renewable resource-derived electricity is considered a promising candidate for clean energy. However, sustainable hydrogen production from water splitting requires highly active catalysts to make the process efficient. Catalysts based on graphene-like two-dimensional (2D) materials present great potential in the hydrogen evolution reaction (HER) and thus gain attention. In this review, which is a combination of our recent works, we highlight research efforts towards electrocatalysts for the HER based on 2D materials including transition metal disulfides, MXenes, and boron monolayers. Finally, we summarize the challenges and prospects for future development of electrocatalysts for the hydrogen evolution reaction.
The crystal facet effect of photocatalysts has aroused increasing attention owing to its importance for the synthesis of novel photocatalysts, understanding photocatalytic mechanisms, and enhancing photocatalytic efficiency. In this paper, the research approaches, recently discovered phenomena, and the application of the facet effect of TiO2 are reviewed. The prospects and challenges of using the crystal facet effect of TiO2 photocatalysts are discussed.
Chemically modified carbon has attracted significant attention since our first report of its use in lithium/sulfur (Li/S) cells. Compared with traditional carbon materials, chemically modified carbon prevents the dissolution and diffusion of intermediate polysulfides. Therefore, it yields sulfur cathodes with long cycling stability, which has become the focus of current research in the field of Li/S batteries. This review summarizes the use of chemically modified carbon for highly efficient sulfur utilization and the synergistic chemical/physical trapping of sulfur species. The prospects of further developments of Li/S batteries using chemically modified carbon is also discussed.
Hydrothermal processing in conjunction with in situ precipitation were successfully applied to synthesize the magnetic composite catalyst silver bromide/silver phosphate/zinc ferrite (AgBr/Ag3PO4/ZnFe2O4). The phase structure, composition, morphology, and optical property of this material were subsequently assessed by X-ray diffraction, energy dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and UV-Vis diffuse reflectance spectroscopy. Under visible light illumination, the as-prepared AgBr/Ag3PO4/ZnFe2O4 photocatalyst exhibited superior photocatalytic performance during rhodamine B (RhB) degradation compared with Ag3PO4/ZnFe2O4, AgBr/ZnFe2O4, and P25 TiO2. This new catalyst also showed excellent photocatalytic activity in both acidic and basic solutions. The RhB photodegradation rate was slightly increased at higher temperatures, and the activation energy for this reaction was determined to be 31.9 kJ·mol-1 according to the Arrhenius equation. The high performance of the AgBr/Ag3PO4/ZnFe2O4 catalyst can be attributed to efficient photo-induced charge separation, and the generation of superoxide radicals and holes that are responsible for RhB degradation.
Lithium-sulfur (Li-S) batteries are promising electrochemical energy storage systems because of their high theoretical energy density, natural abundance, and environmental benignity. However, several problems such as the insulating nature of sulfur, high solubility of polysulfides, large volume variation of the sulfur cathode, and safety concerns regarding the lithium anode hinder the commercialization of Li-S batteries. Graphene-based materials, with advantages such as high conductivity and good flexibility, have shown effectiveness in realizing Li-S batteries with high energy density and high stability. These materials can be used as the cathode matrix, separator coating layer, and anode protection layer. In this review, the recent progress of graphene-based materials used in Li-S batteries, including graphene, functionalized graphene, heteroatom-doped graphene, and graphene-based composites, has been summarized. And perspectives regarding the development trend of graphene-based materials for Li-S batteries have been discussed.
Singlet exciton fission is the process by which a high-energy singlet exciton splits into two low-energy triplet excitons. Organic solar cells based on singlet fission have the potential to exceed the Shockley-Queisser limit and, in doing so, may improve their efficiency from 30% to 44.4%. Although progress in singlet fission materials and photovoltaic devices has accelerated with recent research, many challenges and debates remain with regard to clarifying the relationship between molecule structures and the rate and efficiency of singlet fission. This review addresses recent advances in singlet fission materials and summarizes the work of our own research group. We begin by introducing the background of singlet fission, following with the general concept, the requirements for singlet fission to proceed, and the applications of transient absorption spectroscopy. Two mechanisms have been proposed to explain singlet fission molecules, intermolecular and intramolecular singlet fission, and these two types of materials are summarized, focusing on dimers, which are novel structures that undergo efficient intramolecular singlet fission. Based on the latest developments in singlet fission, we discuss the possible future advances in, and prospects for the application of, singlet fission materials.
Photoelectrochemical water splitting is to utilize collected photo-generated carrier for direct water cleavage for hydrogen production. It is a system combining photoconversion and energy storage since converted solar energy is stored as high energy-density hydrogen gas. According to intrinsic properties and band bending situation of a photoelectrode, hydrogen tends to be released at photocathode while oxygen at photoanode. In a tandem photoelectrochemical chemical cell, current passing through one electrode must equals that through another and electrode with lower conversion rate will limit efficiency of the whole device. Therefore, it is also of research interest to look into the common strategies for enhancing the conversion rate at photoanode. Although up to 15% of solar-to-hydrogen efficiency can be estimated according to some semiconductor for solar assisted water splitting, practical conversion ability of state-of-the-art photoanode has yet to approach that theoretical limit. Five major steps happen in a full water splitting reaction at a semiconductor surface:light harvesting with electron excitations, separated electron-hole pairs transferring to two opposite ends due to band bending, electron/hole injection through semiconductor-electrolyte interface into water, recombination process and mass transfer of products/reactants. They are closely related to different proposed parameters for solar water splitting evaluation and this review will first help to give a fast glance at those evaluation parameters and then summarize on several major adopted strategies towards high-efficiency oxygen evolution at photoanode surface. Those strategies and thereby optimized evaluation parameter are shown, in order to disclose the importance of modifying different steps for a photoanode with enhanced output.
Semiconducting, two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2) have attracted significant attention because of their unique properties and promising applications in electronic and optoelectronic devices. However, the controllable tuning of the properties of 2D MoS2 remains a key challenge with regard to its practical application. Among various approaches to addressing this issue, chemical doping is one of the most efficient. This review focuses on three major doping strategies, which are surface charge transfer, in-plane substitution and interlayer intercalation. We discuss the principles, latest progress and limitations of these doping approaches. Finally, we summarize the current challenges and opportunities associated with the chemical doping of 2D MoS2.
Graphene and graphene-like two-dimensional (2D) materials exhibit broad prospects for application in emerging electronics owing to their unique structure and excellent properties. However, there are still many challenges facing the achievement of controllable growth, which is the main bottleneck that limits the practical application of these materials. Chemical vapor deposition (CVD) is the most effective method for the controllable growth of high-quality graphene, in which the design of the catalytic substrate catches the most attention because it directly determines the two most significant basal processes--catalyzation and mass transfer. Recently, compared with the selection of the chemical composition of the catalyst, the change of the physical state of the catalyst from a solid phase to liquid phase is expected to lead to a qualitative change and improvement in the CVD of graphene and graphene-like two-dimensional materials. Unlike solid substrates, liquid substrates exhibit a loose atomic arrangement and intense atom movement, which contribute to a smooth and isotropic liquid surface and a fluidic liquid phase that can embed heteroatoms. Therefore, liquid metal shows many unique behaviors during the catalyzation of the growth of graphene, graphene-like two dimensional materials, and their heterostructures, such as strict self-limitation, ultra-fast growth, and smooth stitching of grains. More importantly, the rheological properties of a liquid substrate can even facilitate the self-assembly and transfer of 2D materials grown on it, in which the liquid metal substrate can be regarded as the 'philosopher's stone'. This feature article summarizes the growth, assembly, and transfer behavior of 2D materials on liquid metal catalysts. These primary technology developments will establish a solid foundation for the practical application of 2D materials.
Ordered mesoporous carbon materials (OMCs) have potentially broad applications in many fields, such as adsorption, separation, catalysis, and energy storage/conversion. Compared with the elaborate hardtemplate strategy, the soft-template approach, which is based on the self-assembly between amphiphilic block copolymers and polymerizable precursors (e.g., phenolic resins), is a more effective and efficient method for the synthesis of OMCs. In this review, the mechanism and characteristics for three main soft-template methods, i.e., solvent evaporation-induced self-assembly synthesis, aqueous cooperative self-assembly synthesis and solvent-free synthesis, are discussed and compared. In addition, a few highlights of recent progress, including application of novel carbon precursors, structural modification and functionalization of OMCs, are outlined. Finally, we summarize the crucial issues to be addressed in developing the synthesis methodology of OMCs.
A selenium disulfide-impregnated hollow carbon sphere composite was prepared as the cathode material for lithium-ion batteries. The morphology, composition, and structure of the as-synthesized composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and the Brunauer-Emmett- Teller (BET) technique. It was found that uniform monodispersive hollow carbon spheres can be synthesized by the template method combined with chemical polymerization. The diameter of the spheres is about 500 nm and the thickness of their wall is about 30 nm. Furthermore, a selenium disulfide-impregnated hollow carbon sphere composite can be achieved by the melting-diffusion method. The electrochemical performance of the as-synthesized composite as a cathode material for lithium-ion batteries was also investigated. Compared with the pristine bulk SeS2 material, the SeS2@HCS composite exhibits higher initial discharge capacity (956 mAh· g-1 at a current density of 100 mA·g-1), longer cycle life (200 cycles at a current density of 100 mA·g-1), and better rate performance. The results indicate that this composite can be considered as a promising candidate for the cathode material of lithium-ion batteries.
In response to aggravated fossil resources consuming and greenhouse effect, CO2 reduction has become a globally important scientific issue because this method can be used to produce value-added feedstock for application in alternative energy supply. Photoelectrocatalysis, achieved by combining optical energy and external electrical bias, is a feasible and promising system for CO2 reduction. In particular, applying graphene in tuning photoelectrochemical CO2 reduction has aroused considerable attention because graphene is advantageous for enhancing CO2 adsorption, facilitating electrons transfer, and thus optimizing the performance of graphene-based composite electrodes. In this review, we elaborate the fundamental principle, basic preparation methods, and recent progress in developing a variety of graphene-based composite electrodes for photoelectrochemical reduction of CO2 into solar fuels and chemicals. We also present a perspective on the opportunities and challenges for future research in this booming area and highlight the potential evolution strategies for advancing the research on photoelectrochemical CO2 reduction.
As a secondary battery, the Li-air battery has the highest theoretical specific energy and has been considered as one of the most promising power sources for electric vehicles. The Li-air battery based on organic electrolyte has become a topic of interest owing to its excellent theoretical energy density, environmental friendliness and low cost. During the past 20 years, much progress has been made in the development of the reaction mechanism, cathode structure, catalyst and electrolyte materials. But there are still many obstacles to overcome before its practical applications. In this paper, we review some of the latest progress in the research on the reaction mechanism, cathode materials, catalysts, electrolytes, as well as the lithium anode. Future research and development prospects are also discussed.
Organic-inorganic perovskite solar cells (PSCs) have become one of the most promising solar cells, as the power conversion efficiency (PCE) has increased from less than 5% in 2009 to certiﬁed values of over 22%. In the typical PSC device architecture, hole transport materials that can effectively extract and transmit holes from the active layer to the counter electrode (HTMs) are indispensable. The well-known small molecule 2, 2', 7, 7'-tetrakis-(N, N-di-4-methoxy-phenyl amino)-9, 9'-spirobifluorene (spiro-OMeTAD) is the best choice for optimal perovskite device performance. Nevertheless, there is a consensus that spiro-OMeTAD by itself is not stable enough for long-term use in devices due to the sophisticated oxidation process associated with undesired ion migration/interactions. It has been found that spiro-OMeTAD can significantly contribute to the overall cost of materials required for the PSC manufacturing, thus its market price makes its use in large-scale production costly. Besides, another main drawback of spiro-OMeTAD is its poor reproducibility.
To engineer HTMs that are considerably cheaper and more reproducible than spiro-OMeTAD, shorter reaction schemes with simple purification procedures are required. Furthermore, HTMs must possess a number of other qualities, including excellent charge transporting properties, good energy matching with the perovskite, transparency to solar radiation, a large Stokes shift, good solubility in organic solvents, morphologically stable film formation, and others. To date, hundreds of new organic semiconductor molecules have been synthesized for use as HTMs in perovskite solar cells. Successful examples include azomethine derivatives, branched methoxydiphenylamine-substituted fluorine derivatives, enamine derivatives, and many others. Some of these have been incorporated as HTMs in complete, functional PSCs capable of matching the performance of the best-performing PSCs prepared using spiro-OMeTAD while showing even better stability.
In light of these results, we describe the advances made in the synthesis of HTMs that have been tested in perovskite solar cells, and give an overview of the molecular engineering of HTMs. Meanwhile, we highlight the effects of molecular structure on PCE and device stability of PSCs. This review is organized as follows. In the first part, we give a general introduction to the development of PSCs. In the second part, we focus on the introduction of the perovskite structure, device architecture, and relevant work principles in detail. In the third part, we discuss all kinds of molecular HTMs applied in PSCs. Special emphasis is placed on the relationship between HTM molecular structure and device function. Last but not least, we point out some existing challenges, suggest possible routes for further HTM design, and provide some conclusions.
In this work, graphene oxide sheets are cut into graphene quantum dots (GQDs) by acidic oxidation, then GQDs are hydrothermally treated with ammonia (NH3) at 100℃ to form amino-functionalized graphene quantum dots (N-GQDs). Atomic force microscopy (AFM) shows smaller dots in ammonia treated GQDs, and holey graphene structure is directly observed. Fourier transform infrared (FTIR) spectra confirm that NH3 can effectively react with epoxy and carboxyl groups to form hydroxylamine and amide groups, respectively. The absorption and photoluminescence (PL) properties of the samples are determined by ultraviolet-visible-near infrared (UV-Vis-NIR) spectra and steady-state fluorescence spectra. Three PL excitation peaks occurring at around 250, 290, and 350 nm are attributed to C=C related π-π* transition, C-O-C and C=O related n-π* transitions, respectively. After amino functionalization, the C-O-C related n-π* transition is suppressed, and the PL emission spectrum of N-GQDs is less excitation wavelength. The fluorescence quantum yield of the N-GQDs is 9.6%, which is enhanced by 32 times compared with that of the unmodified GQDs (~0.3%). Timeresolved PL spectra are also used to investigate the N-GQDs. The PL lifetimes depend on the emission wavelength and coincide with the PL spectrum, and are different from most fluorescent species. This result reveals the synergy and competition between defect derived photoluminescence and amino passivation of the N-GQDs. Compared with oxygen-related defects, nitrogen-related localized electronic states are expected to have a longer lifetime and enhanced radiative decay rates.
With the rapid development of wearable devices, flexible conductive materials, which are one of the most important components of flexible electronics, have continued to attract increasing attention as important materials. Conventional electrodes mainly consist of rigid metallic materials, and consequently lack flexibility. Some of the strategies commonly used to make flexible metal electrodes include reducing the thickness of the electrode and designing electrodes with unique structural features. However, these techniques are generally complicated and expensive. Nanocarbon materials, especially carbon nanotubes and graphene, are highly flexible and exhibit excellent conductivity, superior thermal stability, good chemical stability, and high transmittance, making them good alternative materials for the preparation of flexible conductors. In this review, we have summarized recent advances towards the development of flexible conductors based on different types of nanocarbon materials, including carbon nanotubes arrays, carbon nanotubes films, carbon nanotubes fibers, graphene prepared using exfoliation or chemical vapor deposition techniques and graphene fibers. We have also provided a brief review of flexible conductive materials based on graphene/carbon nanotube composites, as well as a summary of the synthesis, fabrication and performances of these conductors. Finally, we have discussed the future challenges and possible research directions of flexible conductors based on nanocarbon materials.
Functional materials and devices that can efficiently store and convert energies have attracted a great deal of attention in recent years. The composites of layered double hydroxide and graphene (LDH/G) are important energy materials. They have excellent physical and chemical properties of both components. Furthermore, their performances in energy-related systems can be improved by increasing the electrical conductivity of LDHs by blending graphene and partly preventing the aggregation of graphene sheets using LDH nanostructures. Therefore, LDH/G composites can be used in various energy applications, particularly for developing high-performance supercapacitors and efficient electrocatalysts for electrochemical splitting of water. In this review, we summarize the recent advances on the synthesis of LDH/chemically modified graphene (CMG, e.g., graphene oxide, reduced graphene oxide and their derivatives) composites and their application in electrochemical energy storage and conversion. Furthermore, the challenges and future perspectives in this research field are also outlined.
Metalloporphyrins are a class of metal-organic complexes that exhibit a wide range of interesting properties with prosperous applications in photoelectric conversion devices, catalysis, sensors and medicines. Besides inorganic two-dimensional (2D) materials (e.g., graphene and transitional metal dichalcogenide nanosheets), two-dimensional metal-organic nanosheets have also attracted considerable attention in recent years as interesting materials. Based on the rapid progress of two-dimensional metal-organic and porphyrinoid nanomaterials, this review aims to provide a brief review of the history of two-dimensional metal-organic nanomaterials, followed by a detailed summary of the synthetic methods used to prepare free-standing 2D nanosheets as well as 2D thin film of metalloporphyrins. We have also provided an up-to-date review of the applications of these materials in solar cells, photo- and electric catalysts as well as optical sensors, and a discussion pertaining to the problems associated with the synthesis, properties, and possible applications of metalloporphyrin 2D materials.
Microbial fuel cell (MFC) is a novel bioelectrochemical device that uses a biocatalyst to convert chemical energy stored in organic wastewater into electrical energy. However, multiple factors limit the practical applications of MFCs, such as the high cost of electrode production and their low conversion efficiencies of power density and energy. Therefore, improving the catalytic performance of the electrodes and lowering the cost of electrode production have become focuses in MFC research. Because of the excellent electrical conductivity and catalytic properties of graphene-based hybrid materials, the development of these electrode materials for use in MFCs has attracted much attention. This review summarizes recent advances of graphene-based hybrid electrodes in MFCs. The preparation methods and the catalytic performance of graphene-modified electrodes, metal and non-metallic/graphene hybrid electrodes, metal oxide/graphene hybrid electrodes, polymer/graphene hybrid electrodes, and graphene gel electrodes are discussed in detail. The influence of graphene-based hybrid anodes and cathodes on the electricity generation performance of MFCs is analyzed. Finally, the problems facing graphene-based hybrid electrodes for MFCs are summarized, and the application prospects of MFCs are considered.
Supercapacitors (SCs) have been explored as one of the electrical sources because of their fast charge and discharge rates, good safety, and long cycle life. However, the limited energy densities of SCs hinder their further application. Thus, current research on SCs focuses on increasing their energy density. Enhancing specific capacitance is an effective way to increase energy density. In this review, we describe several approaches to achieve superior electrochemical properties by optimizing electrode materials and electrolytes. Considering electrode materials, their electrochemical performance is related to their specific surface area, pore structure, and electroconductivity. On one hand, the optimization of specific surface area and pore structure can increase their content of exposed active sites as well as electrolyte ion conductivity, which is beneficial for improved specific capacitance. On the other hand, enhanced electroconductivity leads to higher specific capacitance. The specific capacitances of electric double-layer capacitors and pseudocapacitors have been increased by optimizing carbon-based materials and metal hydroxides/oxides, respectively. Moreover, specific capacitance can be further enhanced by adding a redox mediator to the electrolyte as a pseudocapacitive source. This review offers perspectives to aid the development of next-generation supercapacitors with high specific capacitance.
Graphyne is a rapidly rising star material of carbon allotropes containing only sp and sp2 hybridized carbon atoms forming extended two-dimensional layers. In particular, graphdiyne is an important member of graphyne family. With unique nanotopological pores, two-dimensional layered conjugated frameworks, and excellent semiconducting and optical properties, graphdiyne has displayed distinct superiorities in the fields of energy storage, electrocatalysis, photocatalysis, nonlinear optics, electronics, gas separation, etc. Therefore, the synthesis of high-quality graphdiyne is highly required to fulfill its potentially extraordinary applications. Furthermore, the development of a standardized and systematic set of characterization procedures is an urgent need, and would be based on intrinsic samples. However, there are still obvious barriers to synthesizing this new-born carbon allotrope that can be mainly considered as follows. The selection and stability of monomers is essential for synthesis. The synthesis process in solution also suffers from an annoying problem of the relatively free rotation possible about the alkyne-aryl single bonds, which leads to the coexistence and rapid equilibration of coplanar and twisted structures. Furthermore, the limited reaction conversion and side reactions also lead to a confusion of configuration.
In this review, we primarily focus on the state-of-the-art progress of the synthetic strategies for graphdiyne. First, we give a brief introduction about the structure of graphyne and graphdiyne. We subsequently discuss in detail the recent developments in synthetic methods that can mainly be divided into three aspects: total organic synthesis, on-surface covalent reaction, and polymerization in a solution phase. In particular, much progress in solution polymerization has been achieved since in-situ polymerization on Cu surface was reported in 2010. Liquid/liquid interface, gas/liquid interface, and surface template were also employed for confined reaction, and contribute significantly to the synthesis of a graphdiyne film. Through such strategies, graphdiyne with a well-defined structure and diverse morphologies could be achieved successfully. Finally, the opportunities and challenges for the synthesis of graphdiyne are prospected. A more rational design is desired in terms of monomer modification and reaction regulation.
Mixed halide perovskites of MAPbI3-xBrx and MAPbI3-xClx (MA=CH3NH3) with film thickness of about 300 nm were synthesized through the Br or Cl doping, thanks to the two steps deposition of controlled concentration of the precursor solution and the intramolecular exchange of DMSO molecules intercalated in PbI2 (PbI2(DMSO) complex) with MAX (X=I, Br) or MAX (X=I, Cl), respectively. The doping of Br or Cl in the perovskite film can improve the photovoltaic performance of PSCs with the precursor of MAX contains 5% (in mole fraction, same below) MABr or 15% MACl, respectively, while further increase in the content of MABr or MACl in the precursor did not lead to significant changes in doping amounts, but small white particles or pin-holes were formed in mixed perovskite materials, therefore resulted in adverse effects on the performance of solar cells. The MAPbI3-xBrx perovskite solar cells with 5% MABr in precursor solution showed a power conversion efficiency (PCE) of 13.2%, and the MAPbI3-xClx perovskite solar cells with 15% MACl in precursor solution showed the highest PCE of 13.5%.
The frequency of oil-spill accidents and industrial wastewater discharges have caused severe water pollution, not only resulting in huge economic losses but also threatening the ecological system. Recently, researchers have developed different types of materials with special wettability (such as superhydrophobicity or superoleophobicity) and used them successfully for oil-water separation. Superhydrophobic and superoleophobic surfaces can generally be obtained by designing the surface geometric micro-topography and chemical composition of solid materials. Endowing porous materials with reverse super-wettability to water and oil using various microfabrication technologies is the key to separate oil-water mixtures. In this review we initially identify the significance of fabricating oil/water-separating materials and achieving effective separations. Then, the typical theoretical principles underlying surface wettability are briefly introduced. According to the difference in surface wettabilities toward water and oil, we classify the current oil-water separating materials into three categories: (ⅰ) superhydrophobic/superoleophilic materials, (ⅱ) superoleophobic/ superhydrophilic materials, and (ⅲ) smart-response materials with switchable wettability. This review summarizes the representative research work for each of these materials, including their fabrication methods, principle and process of oil-water separation, and main characteristics and applications. Finally, existing problems, challenges, and future prospects of this fast-growing field of special wettability porous materials for the separation of oil-water mixtures are discussed.
Melamine and melem molecules are widely used precursors for synthesizing graphitic carbon nitride (g-C3N4), the latter also a hot two-dimensional material with photocatalytic applications. The molecular structures of both are respectively identical to the repeating units of two distinct g-C3N4 phases. In this work, the adsorption and self-assembly of melamine and melem on an Au(111) surface were investigated with low-temperature scanning tunneling microscopy (STM). Particularly, the patterns of hydrogen bonds (HBs) in their assemblies were identified and compared. It was found that melamine can only form one type of HB and two kinds of assembly structures, whereas melem can form three types of HBs and six kinds of assembly structures in total. Moreover, the involved HBs can be transformed by tip manipulation. These findings may provide a new strategy for tuning the functionality of surface self-assemblies by manipulating intermolecular hydrogen bonds. This also paves a route for the in situ synthesis of g-C3N4 on metallic surfaces and subsequent investigations of their physicochemical properties.
Radiation therapy kills tumor cells via focused high energy radiation, and has become one of the most common and effective clinical treatments for malignant tumors. However, some limitations restrict its clinical efficacy, including a requirement for elevated doses of radiation, side effects due to exposure of healthy tissue, and especially radioresistance of tumor cells. With the development of nanomedicine, multifunctional nanoradiosensitizers offer a new route to improve the efficiency of radiation therapy. In this paper, we summarize the main types of nanoradiosensitizers and their applications in radiation therapy, especially those that have currently entered clinical trials. We also summarize the main approaches to nanomaterials-based radiosensitization, and discuss the factors influencing their application. Finally, the challenges and prospects of multifunctional nanoradiosensitizers are presented.
Nanomaterials have excellent properties and have been used widely in chemical engineering, electronics, mechanics, environment, energy, aerospace, and many other fields in recent years. Besides, nanomaterials have attracted increasing attention in the biomedical field. The interactions between nanomaterials and protein molecules are not only significant to the basic science of the biomedical field, but also crucial for the evaluation of biomedical applications and biosafety of nanomaterials. The interfacial interactions between proteins and nanomaterials could induce a series of changes to the structures and functions of proteins, such as the transformation of protein conformations, and the modulation of aggregation states, which would influence the functions of the protein molecules. Interfacial interactions can also influence the physicochemical features of nanomaterials, including morphology, size, hydrophilicity/hydrophobicity, and surface charge density. In this review we explained the molecular level mechanisms for the interactions between nanomaterials and proteins at the interface based on the detection technologies, and discussed the changes in physical and chemical features, structures, and functions. We envision this review could be helpful for the deeper understanding of the complicated interactions between nanomaterials and proteins, and could be beneficial for promoting the healthy, safe, and sustainable development and application of nanomaterials in the biological and medical fields.
The adsorption of sodium salicylate on goethite or hematite surfaces was investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoemission spectroscopy (XPS), and periodic plane-wave density functional theory (DFT) calculations. The core level shift (CLS) and charge transfer of the adsorbed surface iron sites calculated by DFT with periodic interfacial structures were compared with the X-ray photoemission experiments. The FT-IR results reveal that the interfacial structure of sodium salicylate adsorbed on goethite or hematite surfaces can be classified as bidentate binuclear (V) or bidentate mononuclear (IV), respectively. The DFT calculated results indicate that the bidentate binuclear (V) structure of sodium salicylate is favorable on the goethite (101) surface, with an adsorption energy of-5.46 eV, while the adsorption of sodium salicylate on the goethite (101) surface as a bidentate mononuclear (IV) structure is not predicted, as it has a positive adsorption energy of 3.80 eV. Conversely, on the hematite (001) surface, the bidentate mononuclear (IV) structure of the adsorbed sodium salicylate has anadsorption energy of-4.07 eV, confirming its favorability. Moreover, the calculated CLS of Fe 2p (-0.68 eV) for the adsorbed iron site on the goethite (101) surface is consistent with the experimentally observed CLS of Fe 2p (-0.5 eV) for SSa-treated goethite (goethite after the treatment of sodium salicylate). Our calculated CLS of Fe 2p (-0.80 eV) for the adsorbed iron site on the hematite (001) surface is likewise in good agreement with the experimentally observed CLS of Fe 2p (-0.8 eV) for SSa-treated hematite (hematite after the treatment of sodium salicylate). Thus, goethite is predicted to adsorb sodium salicylate as a bidentate binuclear (V) structure via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to two surface iron atoms of goethite (101). Meanwhile, on the hematite surface, the bidentate mononuclear (IV) complex formed via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to one surface iron atom of hematite (001) can be regarded as plausible.
In this work, Li1.2Mn0.54Co0.13Ni0.13NaxO2 was prepared via an ion-exchange process combined with a solid-state reaction. Aberration-corrected scanning transmission electron microscopy (STEM), energydispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) were all used to study the surface structure and chemical distribution of the resulting material. Nickel (Ni) was found to be enriched at the surface in regions perpendicular to the lithium diffusion channels (that is, the (200) surfaces) and also exhibited a tendency to diffuse into the lithium (Li) layers, generating a Fm3m rocksalt phase. In contrast, cobalt (Co) segregated along the transition metal (TM) layers of the (001) and (200) surfaces. The results of aging trials demonstrated that Co-enriched layers lead to surface structure instability, as evidenced by the formation of a large number of antisite defects (Li-TM) and rocksalt phase structures at the (001) surface during aging.
Polymer light emitting devices incorporating poly(9-vinylcarbazole) (PVK):2, 2'-(1, 3-phenylene)-bis [5-(4-tert-butylphenyl)-1, 3, 4-oxadiazole] (OXD-7) as the co-host and the thermally activated delayed fluorescence compound 2, 4, 5, 6-tetrakis(carbazol-9-yl)-1, 3-dicyanobenzene (4CzIPN) as the emissive dopant exhibited a peak external quantum efficiency of 13%. In addition, 4CzIPN-sensitized (5, 6, 11, 12)-tetraphenyl-naphthacene (Rubrene) devices gave a peak external quantum efficiency of 9.2%, a value that is 5.4 times that of analogous devices without 4CzIPN. Based on transient luminescence measurements, the working mechanism for 4CzIPN sensitization was determined to be F?rster energy transfer from 4CzIPN to Rubrene. This work assessed the effects of the Rubrene concentration and the carrier transport balance in the emission layer on the device properties, and the results suggest that the self-aggregation of Rubrene may limit device efficiency.
Lithium-sulfur batteries are considered to be rather latest and high-performance storage batteries due to their high theoretical specific capacity (1675 mAh·g-1), high energy density (2600 Wh·kg-1), environmental friendliness, low cost, and safety. These features make them important in the field of mobile electric vehicles and portable devices. However, because of rapid capacity attenuation with poor cycle and rate performances, these batteries are far from ideal for commercial applications. This paper reviews the entire and latest studies in lithium-sulfur batteries. Cathodes, electrolyte, separators, and anodes protection are introduced in detail. The existing lithium-sulfur batteries defects and problems are analyzed. Finally, we provide some insights into the future direction and prospects of lithium batteries.
Two-dimensional (2D) materials possess nanoscale thickness with large aspect ratios on the other two dimensions. The ultrahigh surface-to-volume ratio of 2D materials is the most important property different from their bulk counterparts, and is beneficial for mass and heat transport, and ion diffusion. Among the various 2D materials, carbon-based materials have attracted tremendous attentions since the first explosive research on graphene. Therefore, they provide opportunities for applications in adsorption, catalysis, and electrical energy storage. The porous structure of such carbon materials is a key influence on the properties of these 2D materials. This review focuses on recent developments in synthesis strategies for 2D carbon-based materials, especially the preparation of carbon nanosheets and carbon-inorganic hybrids/composites nanosheets. The main factors influencing the porous structure of the material are discussed for each method. Applications of the materials are introduced, mainly in the fields of adsorption, heterogeneous catalysis, and electrical energy storage. Finally, the leading-edge issues of novel 2D carbon-based materials for the future are discussed.
Nanosheet materials obtained from laminar compounds are new two-dimensional anisotropic nanomaterials that can even reach the sub-nanometer scale. These materials possess unique physical and chemical properties. An example of such a nanosheet materials is graphitic carbon nitride (g-C3N4) nanosheets transformed from bulk g-C3N4. Here, g-C3N4 nanosheets were prepared from bulk g-C3N4 by high-temperature thermal oxidation. The photocatalytic activity of eosin (EY)-sensitized g-C3N4 nanosheets for hydrogen evolution was about 2.6 times higher than that of bulk g-C3N4. The structure of the g-C3N4 nanosheets and process of electron transfer between EY and the g-C3N4 nanosheets were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, fluorescence spectroscopy, and photoelectrochemical measurements. The g-C3N4 nanosheets possessed high specific surface area. The g-C3N4 nanosheets not only effectively absorbed dye molecules, but also enhanced the separation and electron transport efficiencies of photogenerated charges because of their quantum confinement effect. The quantum confinement effect of g-C3N4 nanosheets widened their bandgap, improved electron transfer ability along the in-plane direction, and lengthened the lifetime of photoexcited charge carriers. As a result, the photocatalytic activity of the g-C3N4 nanosheets was improved compared with that of bulk g-C3N4.
Numerous real space functions have been purposed so far for unveiling chemically interesting molecular electronic structure characteristics, such as chemical bonds, lone pairs, and multicenter electronic conjugations. Among these analysis methods, electron localization function (ELF), Laplacian of electron density (∇2ρ), and deformation density (ρdef) were widely employed in practical research work. It is well known that the analysis of total molecular electron density is not sufficient for revealing much information about the molecular electronic structure like the above-mentioned methods. However, in this work, using several instances and by comparing with the ELF, ∇2ρ, and ρdef values, we show that it is possible to explore molecular electronic structure characteristics if one solely focuses on investigating the valence electron density distribution. It is found that for most cases, analysis of the very simple valence electron density conveys analogous information as ELF, ∇2ρ and ρdef analyses, with additional advantage of reduced computational complexity. We hope that this work will bring chemists' attention to the high importance of valence electron density, which has been largely ignored for a long time. It should also be noticed that the valence electron density analysis is not free from drawbacks, and when this method is unable to provide an informative picture, one has to use other analysis methods.
Non-precious metal catalysts should be studied to substitute precious Pt catalysts. Recent developments of non-precious-metal catalysts (combined with the achievements of our group) are summarized in this paper. The main issues that exist in the transition metal oxides, metal-nitrogen-carbon material, and heteroatom-doped carbon material are highlighted from the aspects of the synthetic methods and mechanisms. The research tendency and perspective of these non-precious metal catalysts are provided.
Three-dimensional direct numerical simulation is conducted to simulate the auto-ignition of the highoctane fuel PRF70 under partially premixed combustion (PPC) engine conditions. A skeletal primary reference fuel (PRF) chemical kinetic mechanism is adopted, including 33 species and 38 elementary reactions. Compression/expansion effects caused by piston motion, the real engine geometry, and the working conditions are considered. The simulation includes two injections, the first being used to form a relatively uniform base mixture and the second to forma stratified mixture and trigger the ignition. It is found that the combustion process in PPC engines is a rather complex combination of homogeneous combustion, rich premixed and diffusioncontrolled combustion. The region between the two injections is near stoichiometry, resulting in the formation of NOx, while abundant CO is retained in the region with equivalence ratio (φ) > 2, which needs to diffuse to meet the oxidizer and burn in a diffusion flame. The marching cube method is used to extract the 3D flame surface and show the temporal evolution of the reaction front. Finally, the joint PDF of the Gaussian curvature (kg) and principle mean curvature (km) and temporal evolution of the probability density function (PDF) in terms of km show that km plays a more important role and becomes negative as time evolves because of the consumption of rich premixed flame in the center.
ZnO has attracted extensive research in perovskite solar cells because of its high electron mobility, spectacular optical transparency, low-temperature processing, and ease of synthesis. Traditional electrode buffer layers used in perovskite solar cells have shown some drawbacks, such as high-temperature treatment, low transmittance, and complex fabrication procedures, which might not be fit for the further development of high-performance flexible perovskite solar cells. Here, we intend to give a systematic introduction to the fabrication and functions of ZnO electrode buffer layers (sol-gel method, pre-fabricated ZnO nanoparticle suspension, atomic layer deposition, spray pyrolysis, electrodeposition, chemical bath deposition, radio-frequency sputtering, metal organic chemical vapor deposition, and magnetron sputtering etc.). Particular attentions were paid to the understanding of the structure-property relations between the thickness, morphology, doping, and composition of ZnO electrode buffer layers and the performance of perovskite solar cells (open circuit voltage, current density, fill factor, power conversion efficiency, etc.). A perspective on the future development of ZnO electrode buffer layers and their applications in perovskite solar cells were also discussed in this review.
A highly ordered mesoporous Si/C composite was prepared by magnesiothermic reduction method, using SBA-15 as the precursor at 660 ℃ with subsequent carbon coating. This Si/C composite preserved the ordered honeycomb pore channels of SBA-15 and exhibited a lotus root-like structure with high packing density. A liquid ambient reaction model is proposed to explain the reaction between SBA-15 and magnesium powder at 660 ℃ as well as the mechanism by which the highly ordered mesoporous structure is generated. The phase composition and morphology of this material were analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption and Raman spectroscopy. The excellent electrochemical performance of the as-prepared material suggests potential applications as an anode material in second-generation Li-ion batteries.
Polymer solar cells (PSCs) with bulk heterojunction (BHJ) structures have seen rapid development in recent years. In comparison with their inorganic counterparts, PSCs have some advantages such as low cost, light weight, solution processability, and good mechanical flexibility. However, improvement of the power conversion efficiency (PCE) of PSCs is required for commercial applications. In order to achieve high-performance PSCs, active layers, including donor polymers and acceptors, are very important. Several design principles for conjugated donor polymers in PSCs have emerged, including optimization of the conjugated backbone, side-chains, and substituents. In the past few decades, various classes of electron-donating polymers have been reported for PSCs. Among them, quinoxaline (Qx) is a unique building block for the construction of different optoelectronic polymers because of its planar, rigid, and conjugated structure. Qx derivatives have proven interesting and have been widely employed in many fields. Qx-based conjugated polymers (or small molecules) can be easily modified to match with ball-like fullerene derivatives such as PCBM ([6, 6]-phenyl-C61 or C71-butyric acid methyl ester) or weak crystalline non-fullerene acceptors such as 2, 2'-[[6, 6, 12, 12-tetrakis(4-hexylphenyl)-6, 12, -dihydrodithieno[2, 3-d:2', 3'-d']-s-indaceno[1, 2-b:5, 6-b']dithiophene-2, 8-diyl]bis[methylidyne(3-oxo-1H-indene-2, 1(3H)-diylidene)]]bispropanedinitrile (ITIC). Herein, we synthesized a Qx-based polymer with asymmetric side-chains (TPQ-1). The molecular weight, optical properties, molecular energy levels, and mobilities of TPQ-1 were investigated. Furthermore, the blend morphologies and photovoltaic properties of TPQ-1 using a strong crystalline non-fullerene (NF) acceptor (o-IDTBR) were systematically explored. The photovoltaic performance of TPQ-1 and its symmetric side-chain counterpart, HFQx-T, was compared. The introduction of asymmetric side-chains led to a favorable phase separation when blended with o-IDTBR. As expected, the TPQ-1:o-IDTBR-based devices exhibited a high PCE of 8.6% after thermal annealing (TA). In contrast, the HFQx-T:o-IDTBR-based devices showed a moderate PCE of 5.7%, moreover, the PCE was decreased to 4.6% after TA treatment. More importantly, a low bandgap material, PTB7-Th, was specifically selected as a third component to mix with the TPQ-1:o-IDTBR blend to form highly-efficient ternary PSCs. At an optimal weight ratio (15%) of PTB7-Th addition, a PCE of 9.6% was achieved. In the systems that were investigated, TPQ-1 demonstrated significantly better photovoltaic properties than the HFQx-T-based devices. These results indicate that Qx-based polymers with asymmetric side chains have a bright future in photovoltaic devices.
Proton exchange membrane fuel cells (PEMFCs) are considered as ideal alternative power devices to traditional internal combustion engines for automobile applications because of their high electric power density, high energy conversion efficiency, and low environmental impact as well as low temperatures for start-up and operation. However, PEMFCs normally require a high loading of the expensive precious metal platinum (Pt) as the electrocatalytic material to maintain desirable energy output. Thus, the development of novel catalysts with lower Pt loading, enhanced activity, and improved durability is vital for the scalable commercialization of PEMFC technology. In this regard, core-shell structure has been demonstrated as an effective strategy to minimize the amount of Pt in PEMFCs because of the following two factors:(1) a core-shell architecture with a Pt-rich shell and M-rich (M represents an earth-abundant element) core can greatly improve the utilization of Pt; (2) the activity and stability of Pt on the surface can be greatly enhanced by strain (geometry) and electronic (alloying) effects caused by the M in the core. First, we briefly discuss the structure-performance relationship of typical core-shell structured electrocatalysts for the oxygen reduction reaction (ORR). Then, we review the development of Pt-based core-shell structured catalysts for the ORR. Finally, a perspective on this research topic is provided.
Phosphorene is a novel two-dimensional material that is more advanced than graphene. This material possesses excellent physical, chemical, and mechanical properties, which are useful for potential applications in a variety of electronic devices. Thus far, a comprehensive review on the latest fabrication methods, property tuning, and applications of phosphorene is lacking. Therefore, a comprehensive review of the synthetic methods, structures, properties, modification methods, and device applications of phosphorene has been presented. The preparation strategies of phosphorene including top-bottom and bottom-up methods have been introduced, followed by a summary of its structure and properties. The modification methods of phosphorene have also been discussed. Finally, the applications of phosphorene in electronic devices have been discussed in detail. Future prospects and potential research areas of phosphorene have also been presented in this review.
Graphene and its derivatives have attracted increasing attention during the last decade as efficient materials for the storage and conversion of energy. In most cases, however, these graphene materials possess large numbers of structural defects such as cavities, heteroatoms and functional groups, making them quite different from the precisely-defined "single carbon layer of graphite" observed for graphene. These materials also differ considerably in terms of their electrochemical properties because of their variable structures, which are strongly influenced by the methods used during their preparation. Structural analyses have indicated that these materials consist of graphene subunits, which are interconnected by organic linkers with properties lying between those of graphene and polymers, which we have defined as "graphenal polymers". The thermal crosslinking reactions of porous polymer networks fabricated from small organic molecules using a bottom-up strategy also result in graphene-like subunits, which are covalently interconnected by polymeric fractions. These materials cover a series of transitional intermediates belonging to the "graphenal polymers" family, where polymers and graphene sit at opposite ends of family spectrum. Moreover, the special structures and properties of these materials make them ideal electrode materials for the storage and conversion of energy via electronic and ionic transport pathways, allowing for a deeper evaluation of the structure-property relationships of different electrode materials.
Based on the first principles method of density functional theory, the band structure and optical absorption properties of single-layered MoS2 doped with Se were calculated. Additionally, its effect on the properties of water splitting was analyzed. The calculations showed that the intrinsic MoS2 monolayer has a direct band gap structure with a value of 1.740 eV. The bottom edge of the conduction band was 0.43 eV above the reduction potential of H+/H2, while the top edge of the valence band was only 0.08 eV below the oxidation potential of O2/H2O. The results indicated that the intrinsic MoS2 monolayer has the potential for the photocatalytic decomposition of water when exposed to visible light. However, as the values of the oxidation and reduction processes were not balanced, the water splitting efficiency of a single-layer MoS2 photocatalyst would be low. When the MoS2 layer was doped with Se the band gap decreased to 1.727 eV, while the corresponding optical absorption spectrum was almost unchanged, and the formation energy of the system was relatively low. These results indicated that single-layered MoS2 should be thermally stabile following doping with Se. Significantly, the bottom edge of the conduction band decreased to 0.253 eV above reduction potential of H+/H2, while the top edge of the valence band increased to 0.244 eV below the oxidation potential of O2/H2O. Thus, the oxidation and reduction processes were balanced, and the water splitting efficiency of single-layered MoS2 should be greatly improved when exposed to visible light.
Halide perovskites have recently emerged as promising materials for low-cost, high-efficiency solar cells. The efficiency of perovskite-based solar cells has increased rapidly, from 3.8% in 2009 to 22.1% in 2016, with the use of all-solid-state thin-film architecture and by engineering cell structures with mixed-halide perovskites. The emergence of perovskite solar cells has revolutionized the field not only because of their rapidly increased efficiency, but also their flexibility in material growth and architecture. The superior performance of the perovskite solar cells suggested that perovskite materials possess intrinsically unique properties. In this review, we summarize recent theoretical investigations into the structural, electrical, and optical properties of halide perovskite materials in terms of their applications in solar cells. We also discuss some current challenges of using perovskites in solar cells, along with possible theoretical solutions.
Aerogels have been developed rapidly in recent years due to their excellent physicochemical properties and broad range of applications. However, most efforts have been devoted to traditional aerogel 3D monoliths, and particular requirements regarding the shape and size of the aerogels for some special uses have been neglected. Shaping aerogel into microspheres, that is, the fabrication of aerogel microspheres, may facilitate potential applications and extension of the range of applications of porous microspheres. Herein, we will present the fabrication and performance of various aerogel microspheres such as silica aerogel microspheres, cellulose aerogel microspheres, RF/carbon aerogel microspheres, and graphene aerogel microspheres. The current challenges and future developments of the aerogel microspheres are also discussed briefly in this review.
To understand the physical and chemical responses of energetic materials, such as 1, 3-dinitrobenzene (DNB, C6H4N2O4), hexanitrohexaazaisowurtzitane (CL20, C6H6N12O12), and CL20/DNB co-crystal, to femtosecond laser ablation (FLA), their molecular reaction dynamics have been investigated using the ReaxFF/ lg force field. The computational results indicate that the temperature and pressure of the CL20/DNB system jump during FLA. In particular, the temperature and pressure gradually reach their maxima following an initial cooling process. N―NO2 bond breaking of the CL20 molecule triggers the reactions for both the CL20 and CL20/ DNB systems. However, the CL20 system prevails the CL20/DNB co-crystal in the decomposition rate simply because coexistence of DNB molecules in the mixture and generated decomposition products containing benzene rings greatly reduce the effective collision probability between CL20 and the products.
Nitrile-modified 2, 5-di-tert-butyl-hydroquinones were synthesized and investigated as redox shuttle overcharge additives for LiFePO4/Li cells. The cyanoethylation reaction was utilized to synthesize the target molecules 2, 5-di-tert-butyl-1, 4-di(β-cyanoethoxyl)benzene (RS-DCN) and 2, 5-di-tert-butyl-1-(β-cyanoethoxyl)-4-methoxybenzene (RS-MCN) in high efficiency from 2, 5-di-tert-butyl-hydroquinone and acrylonitrile. The solubility, cyclic voltammetric measurements, 5 V overcharge test, 100% overcharge test, high rate performance under 100% overcharge conditions, and cycle performance under normal conditions were studied in detail for the electrolyte with the addition of RS-DCN or RS-MCN. The RS-MCN compounds with the asymmetric structure delivered better solubility (with max. 0.3 mol·L-1 in 1.0 mol·L-1 LiPF6/EC+DEC+EMC, 1 : 1 : 1, in vol.), higher overcharge protection life (over 1200 h for the 5 V overcharge test), and excellent rate performance under 100% overcharge conditions (specific discharge capacity reached 153.5 mAh·g-1 at 2.5C). The addition of RS-MCN also improved the cycling performance of the LiFePO4/Li cell under the charge-discharge voltage range of 2.5-3.8 V.
The high cost of platinum in catalyst layers hinders the commercialization of proton exchange membrane fuel cells. This Account reviews recent progress on core-shell nanostructures for oxygen reduction reaction (ORR) in acidic media, which is the cathodic reaction in fuel cells. The synthesis, characterization and evaluation of different types of core-shell electrocatalysts are summarized. Various strategies to improve the performance of core-shell electrocatalysts, including dealloying, morphology control, and surface modification are presented. The issues of mass production and fuel cell performance of core-shell electrocatalysts are also discussed.
Solution-processable organic photovoltaic cells (OPVs) have attracted considerable interest.Over the past twenty years, fullerene and its derivatives have been predominately used as the electron acceptor materials to fabricate OPV devices.In recent few years, non-fullerene organic photovoltaic cells (NF-OPVs), consisting of polymers as the donors and the non-fullerene (NF) materials as the acceptors, have been developed rapidly, and the highest power conversion efficiencies of NF-OPVs exceed those of fullerene-based OPVs.In these NF-OPVs, both polymeric donor materials and NF acceptors play critical roles in achieving outstanding efficiencies, and hence, the molecular design of the polymer donors has been deemed a very important topic of research in the field.In this review, we will present an introduction of the specific requirements for polymer donors in NF-OPVs and summarize the recent progress related to polymer donors for the applications in highly efficient NF-OPVs.
The production of 2, 3-pentanedione from lactic acid over SiO2-supported alkali metal nitrates under various conditions was investigated. Using nitrate (NO3-) as the anion, the effect of alkali metal cations on Claisen condensation of lactic acid into 2, 3-pentanedione was focused on. Among precursors such as LiNO3, NaNO3, KNO3, and CsNO3, CsNO3 displayed the best catalytic performance. Characterization of the fresh and used catalysts by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy revealed that all MNO3 (M=Li, Na, K, Cs) salts were transformed into alkali metal lactates during the reaction. Alkali metal lactates were identified as active species for catalytic Claisen condensation of lactic acid into 2, 3-pentanedione. CO2 temperature-programmed desorption (TPD) results of the used catalysts showed that the CsNO3/SiO2 catalyst was the most alkaline. For that reason, the CsNO3/SiO2 catalyst displayed the highest catalytic performance of those examined. The effects of reaction temperature and loading amount of CsNO3 on reaction performance were also discussed. Over the 4.4% (x, molar fraction) CsNO3/SiO2 catalyst, a 54.1% yield of 2, 3-pentanedione was achieved at 300 ℃.
The solution-processable, anthraquinone-based, fluorene bipolar fluorescent material 2-(9, 9'-bis (2-ethylhexyl)-9H-fluoren-2-yl)anthracene-9, 10-dione (FAA) was synthesized via a Suzuki reaction. The photophysical properties of FAAwere subsequently investigated by acquiring absorption and photoluminescence spectra, and its optical properties were studied using computational density functional theory methods. Data obtained from single-carrier devices incorporating FAA demonstrated its well-matched bipolar charge-transport characteristics. The electroluminescence performance of this material was also examined by doping FAA into a 1, 3-di(9H-carbazol-9-yl)benzene (mCP) matrix as the light-emitting layer via spin coating to produce an organic light-emitting diode (OLED) with an indiumtin oxide (ITO)/poly(3, 4-ethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS)/mCP:FAA/3, 3'-(5'-(3-(pyridin-3-yl)phenyl)-[1, 1':3', 1"-terphen-yl]-3, 3"-diyl)dipyridine (TmPyPb)/ LiF/Al structure. This device exhibited a maximum luminance of 1719 cd·m-2 with a turn-on voltage of 7.4 V, along with maximum current and power efficiencies of 1.66 cd·A-1 and 0.56 lm·W-1, respectively. The electroluminescence mechanism of the OLED is discussed based on the energy level diagrams of the functional layers.
Electrochemicalenergy storage devices are becoming increasingly important in modern societyfor efficient energy storage. The use of these devices is mainly dependent onthe electrode materials. As a newly discovered carbon allotrope, graphdiyne(GDY) is a two-dimensional full-carbon material. Its wide interlayer distance(0.365 nm), large specific surface area, special three-dimensional porousstructure (18-C hexagon pores), and high conductivity make it a potentialelectrode material in energy storage devices. In this paper, based on thefacile synthesis method and the unique porous structure of GDY, theapplications of GDY in energy storage devices have been discussed in detailfrom the aspects of both theoretical predictions and recent experimentaldevelopments. The Li/Na migration and storage in mono-layered and bulk GDYindicate that GDY-based batteries have excellent theoretical Li/Na storagecapacity. The maximal Li storage capacity in mono-layered GDY is LiC3(744 mAh∙g-1). The experimental Li storage capacity of GDY issimilar to theoretical predictions. The experimental Li storage capacity of athick GDY film is close to that of mono-layered GDY' (744 mAh∙g-1).A thin GDY film with double-side storage model has two-times the Li storagecapacity (1480 mAh∙g-1) of mono-layered GDY. Powder GDY has lower Listorage capacity than GDY film. The maximal Na storage capacity in GDYcorresponds to NaC5.14 (316 mAh∙g-1), and mono-layeredGDY possesses higher theoretical Na storage capacity (NaC2.57). Theexperimental Na storage capacity (261 mAh∙g-1) is similar to itstheoretical value. Besides, GDY as electrode material, applied in metal-sulfurbatteries, presents excellent electrochemical performance (in Li-S battery: 0.1C, 949.2 mAh∙g-1; in Mg-S battery: 50 mA∙g-1, 458.9 mAh∙g-1).This ingenious design presents a new way for the preparation of carbon-loadedsulfur. GDY electrode material is also successfully used in supercapacitors, including the traditional supercapacitor, Li-ion capacitors, and Na-ioncapacitors. The traditional supercapacitor with GDY as the electrode material showsgood double layer capacitance and pseudo-capacitance. Both Li-ion capacitor(100.3 W∙kg-1, 110.7 Wh∙kg-1) and Na-ion capacitor (300W∙kg-1, 182.3 Wh∙kg-1) possess high power and energydensities. Moreover, the effects of synthesis of GDY nanostructure, heattreatment of GDY, and atom-doping in GDY on the performance of electrochemicalenergy storage will be introduced and discussed. The results indicate that GDYhas great potential for application in different energy storage devices as anefficient electrode material.
Perovskite solar cells have undergone rapid development because of their high solar absorption efficiencies, long carrier lifetime and diffusion length, high tolerance to lattice defects, and tunable bandgaps. In the past few years, the solar energy conversion efficiency of the perovskite solar cells has increased to 22.1%. However, despite their promising prospects, as demonstrated by the laboratory-fabricated prototypes, lead toxicity and instability of perovskite solar cells severely impeded their industrialization and applications. Recently, inorganic lead-free perovskite solar cells (such as ABX3 and A2BB'X6), which use Sn, Ge, Bi, Ag, and other metals as replacements for Pb, and Cs and Rb as replacements for methylamine, have been pursued as potential solutions for the toxicity and stability issues. This review highlights the recent research efforts in the development of inorganic lead-free perovskite solar cells and provides a perspective on future developments.
Atomic force microscopy (AFM) is used to investigate surface structures by measuring the interaction force between the tip and sample. Non-contact AFM (NC-AFM) that incorporates a qPlus sensor further enhances the spatial resolution of scanning probe microscopy based on traditional AFM principles. In this perspective, we give a brief introduction to the mechanisms of high-resolution imaging and force measurements using NC-AFM. We then summarize recent applications of NC-AFM in the fields of on-surface chemical reactions, low-dimensional materials, surface charge distribution in molecules, as well as technical improvements and developments of NC-AFM technologies. The opportunities and challenges for NC-AFM technologies are also presented.
The effects of Li, Na, and K alkali metal ions on the band structures and carrier transfer of graphitic carbon nitride (g-C3N4) are investigated using the plane-wave ultrasoft pseudopotential method. The generalized gradient approximation and local density approximation are used to calculate total energies of six adsorption configurations. The three alkali ions all tend to adsorb on the large central cavity (F position) in g-C3N4 layers. The calculated band structures and work function values indicate that the interface charge balance of the n-type Schottky junctions formed between the alkali metal ions and g-C3N4 induces the total band edge potential of g-C3N4 to shift down by 1.52 V (Li), 1.07 V (Na), and 0.86 V (K). The incorporation of K ion adjusts the valence and conduction bands to more appropriate redox potentials than those of pure g-C3N4, and increases the distribution of the HOMO and LOMO of g-C3N4, which helps to improve the mobility of carriers. Meanwhile, the non-coplanar HOMO and LOMO favor the separation of electrons and holes.
In recent years, deep eutectic solvents (DESs) have attracted considerable attention. They have been applied in many fields such as dissolution and separation, electrochemistry, materials preparation, reaction, and catalysis. The DESs are generally formed by the hydrogen bonding interactions between hydrogen-bond donors (HBDs) and acceptors (HBAs). Knowledge of the thermal stability of DESs is very important for their application at high temperatures. However, there have been relatively few studies on the thermal stability of DESs. Herein, a systematic investigation on the thermal stability of 40 DESs was carried out using thermal gravimetric analysis (TGA), and the onset decomposition temperatures (Tonset) of these solvents were obtained. The most important conclusion drawn from this work is that the thermal behavior of DESs is quite different from that of ionic liquids. The anions or cations of ionic liquids decompose first, followed by the decomposition of the opposite ion at elevated temperatures. On the other hand, the DESs generally first decompose to HBDs and HBAs at high temperatures through the weakening of the hydrogen bond interactions. Subsequently, the HBDs with relatively low boiling points or poor stabilities undergo volatilization or decomposition; the HBAs also undergo volatilization or decomposition but at a higher temperature. For example, the most commonly used HBA choline chloride (ChCl) begins to decompose at around 250 ℃. The hydrogen bond plays an important role in the thermal stability of DESs. It hinders the "escape" of molecules and requires greater energy to break than pure HBAs and HBDs, which causes the Tonset of DESs to shift to higher temperatures. Note that the thermal stability of HBDs has a crucial effect on the Tonset of DESs. The HBDs would decompose or volatilize first during TGA because of their relatively poor thermal stability or lower boiling points. The more stable the HBDs are, the greater would be the Tonset values of the corresponding DESs. Further, the effects of anions on HBAs, molar ratio of HBAs to HBDs, and heating rate in fast scan TGA have been discussed. As the heating rate increased, the TGA curves of DESs shifted to higher temperatures gradually, and the temperature hysteretic effect became prominent when the rate reached 10 ℃?min?1. From an industrial application point of view, there is an overestimation of the onset decomposition temperatures of DESs by Tonset, so the long-term stability of DESs was investigated at the end of the study. This study could help understand the thermal behavior of DESs (progressive decomposition) and provide guidance for designing DESs with appropriate thermal stability for practical applications.
The effect of Li+, Zn2+, and Mn2+ ions in aqueous solution on the electrochemical performance of the MnO2 cathode characterized by different crystal structures and morphologies was investigated. The energy storage mechanism of MnO2 in the mixed solution was probed. The results show that in aqueous solution without Mn2+ ions, various MnO2 electrodes exhibit similar electrochemical performance with low capacity and severe attenuation. In an aqueous solution with Zn2+ ions, the capacity of MnO2 electrodes is enhanced, which can be attributed to insertion/extraction of zinc ions. However, the decay of the capacity is drastic. When aqueous solutions containing Mn2+ and Zn2+ ions are used, particle aggregation and crystal structure collapse of MnO2 are effectively prevented owing to the synergistic effect of zinc and manganese ions and the redox reaction process of Mn2+ ions. The negative influence of the ZnSO4·3Zn(OH)2 impurity is also weakened. As a result, the high capacity of MnO2 electrodes resulting from insertion/extraction of zinc ions is maintained (~200 mAh·g-1 at 100 mA·g-1) with excellent cycling stability.
Photoelectrochemical (PEC) bioanalysis is a newly emerged and rapidly developing analysis technique that provides an elegant route for sensitive bioanalysis. The sensing mechanism of PEC bioanalysis is based on the fact that variations in photocurrent signal can be produced by biological interactions between various recognition elements and their corresponding targets. Owing to its excellent sensitivity, selectivity, and great potential for future bioanalysis, PEC bioanalysis has drawn increasing research attention and substantial progress has been made in its analytical applications. Currently, it has become a hot research topic and its recent momentum has grown rapidly, as demonstrated by the increased number of published research articles. Given the pace of advances in this area, this review first introduces the fundamentals and general instrumentation of this methodology. Then, with recent illustrative examples, we summarize the new developments in PEC bioanalysis according to its main bioanalytical applications, i.e., direct PEC detection of biomolecules, PEC enzymatic bioanalysis, PEC DNA detection, and PEC immunoassay. The future challenges and developments in this field are also discussed.
With the widespread use of mobile electronic devices and increasing demand for electric energy storage in the transportation and energy sectors, lithium-ion batteries (LIBs) have become a major research and development focus in recent years. The current generation of LIBs use graphite as the anode material, which has a theoretical capacity of 372 mAh·g-1. Tin-based materials are considered promising anode materials for next-generation LIBs because of their favorable working voltage and unsurpassed theoretical specific capacity. However, overcoming the rapid storage capacity degradation of tin caused by its large volumetric changes (>200%) during cycling remains a major challenge to the successful implementation of such materials. In this paper, SnO2 nanoparticles with a diameter of 2-3 nm were used as active materials in LIB anodes and a threedimensional (3D) graphene hydrogel (GH) was used as a buffer to decrease the volumetric change. Typically, SnCl4 aqueous solution (18 mL, 6.4 mmol·L-1) and graphene oxide (GO) suspension (0.5% (w, mass fraction), 2 mL) were mixed together via sonication. NaOH aqueous solution (11.4 mmol·L-1, 40 mL) was slowly added and then the mixture was stirred for 2 h to obtain a stable suspension. Vitamin C (VC, 80 mg) was then added as a reductant. The mixture was kept at 80℃ for 24 h to reduce and self-assemble. The resulting black block was washed repeatedly with distilled deionized water and freeze-dried to obtain SnO2-GH. In this composite, GH provides large specific surface area for efficient loading (54% (w)) and uniform distribution of nanoparticles. SnO2-GH delivered a capacity of 500 mAh·g-1 at 5000 mA·g-1 and 865 mAh·g-1 at 50 mA·g-1 after rate cycling.This outstanding electrochemical performance is attributed to the 3D structure of GH, which provides large internal space to accommodate volumetric changes, an electrically conducting structural porous network, a large amount of lithium-ion diffusion channels, fast electron transport kinetics, and excellent penetration of electrolyte solution. This study demonstrates that 3D GH is a potential carbon matrix for LIBs.
Sodium ion batteries (SIBs), a promising substitute for lithium ion batteries (LIBs), have attracted extensive attention due to the abundance and low cost of sodium resources. In addition, flexible sodium-ion batteries may be able to satisfy the demands of large-scale energy storage applications for portable, wearable, and flexible electronics. Compared to the development of cathode materials, the progress on anode materials has been relatively slow. Therefore, the exploration of low-cost anode materials with high Na+ storage capacity is very important. Herein, we present oxygen-deficient Na2Ti3O7 nanobelts grown on carbon cloth (CC) as a promising novel flexible anode material for SIBs. Free-standing Na2Ti3O7 nanobelts with oxygen vacancies were directly grown on CC through a simple hydrothermal and thermal reduction process. Benefiting from the improved conductivity and increased active sites after the introduction of oxygen vacancies, the new material exhibits a high reversible capacity of 100 mAh·cm-2 at 200 mA·cm-2, with almost 80% capacitance retention after 200 cycles. When the current density was increased to 400 mA·cm-2, a high capacity of 69.7 mAh·cm-2 was achieved, which is three times that of bare Na2Ti3O7 nanobelts on CC. This 3D oxygen-deficient electrode can significantly promote the transport of Na+ ions and electrons, leading to remarkably improved electrochemical properties. Furthermore, this work constitutes a promising strategy to rationally design and fabricate novel Na2Ti3O7-based anodes with enhanced capacitive behavior, which hold great promise for energy storage/conversion devices, facilitating the large-scale implementation of high-performance flexible SIBs.
Aqueous foams are a typical type of soft matter that are widely used in detergents, cosmetics, food engineering, and oil and gas production because of their relatively small particle size, large superficial area and good fluidity. The stability of a foam plays a crucial role in determining its performance in practical applications. Smart foams, with controllable stability, have been developed recently and their stability can be regulated by external stimuli. This review article mainly focuses on the recent progress in intelligent aqueous foams. To date, smart aqueous foams with temperature, light, magnetic field, pH and CO2-responsive behaviors have been obtained by introducing sensitive groups into foaming agent molecules or adding stimuli-responsive particles to foaming systems. The formation mechanism and properties of different types of smart aqueous foams are summarized and discussed. The potential applications and future prospects of smart foams are also considered.
Three-dimensional, nanoporous CoFe2O4 catalysts were synthesized, employing a colloidal crystal template method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption were subsequently used to characterize the crystal structures and morphologies of the samples. The catalytic activities of nanoporous CoFe2O4 and CoFe2O4 nanospheres during the thermal decomposition of ammonium perchlorate (AP) were also investigated by differential scanning calorimetry (DSC). The results show that the spinel framework of these materials has an ordered open network of pores averaging 200 nm in diameter. The specific surface area of the nanoporous CoFe2O4 was 55.646 m2·g-1, a value that was higher than that of the nanosphere material. DSC analysis indicates that the catalytic activity of the nanoporous CoFe2O4 is superior to that of the spherical material during the thermal decomposition of AP, and that the nanoporous catalyst makes the peak temperature of high temperature decomposition decrease by 91.46℃. The heat release from the AP in the presence of nanoporous CoFe2O4 (1120.88 J·g-1) is 2.3 times that obtained frompureAP. Both the higher specific surface area and greater quantity of active reduction sites on the nanoporous CoFe2O4 relative to the nanosphere material act to reduce the activation energy during the AP decomposition process. Based on the results of this work, a possible catalytic mechanismfor the thermal decomposition of AP over nanoporous CoFe2O4 is proposed, in which gaseous intermediates play an important role.
5-(Benzyloxy)-isophthalic acid (BIC) derivatives and heptanol (HA) molecules adsorb on a highly oriented pyrolytic graphite (HOPG) surface. The surface forms a 2D network structure through weak hydrogen bond interactions. We used molecular dynamics to simulate this adsorption process and perform quantitative analysis of the characteristic parameters, such as the structure geometry, amount of energy, and the number, length and angle of the hydrogen bonds. We compared these results with the experimental result and performed correlational research on the forming tendency and stability between the hydrogen bonds and the chiral selfassembled structure.
We devised and fabricated a Pd/Ni(OH)2 composite catalyst with low noble metal content that grows in situ on nickel foam (NF) using the hydrothermal synthesis method. The morphology and microstructure of the catalyst were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The hydrogen evolution performance of the composite catalyst was evaluated by linear scanning voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CP). The composite catalyst exhibited a special nanostructure consisting of an ultra-thin Ni(OH)2 film growth on the surface of the nickel foam with palladium nanoparticles uniformly embedded in the Ni(OH)2 thin film. The Ni(OH)2 on the surface of the catalyst might considerably promote the dissociation of water and the formation of hydrogen intermediates (Had) that subsequently adsorbed on the nearby Pd and quickly recombined into hydrogen molecules. The composite catalyst exhibits a synergistic effect for the hydrogen evolution reaction (HER), which might decrease the over-potential of hydrogen evolution and enhance the activity of the hydrogen evolution reaction. Growing the composite catalyst in situ on the nickel foam effectively improved the stability of the catalyst for the HER in alkaline solutions.
The properties of Pd nanocrystals (NCs) intended for use in electrocatalytic applications greatly depend on their surface structures and morphologies. Recent developments in the shape-controlled synthesis of polyhedral Pd NCs represent a promising means of precisely tuning their electrocatalytic properties, and thus may enable the performance enhancement of electrocatalytic Pd NCs. In this comprehensive review, we concentrate on the most important current research concerning the shape-controlled synthesis of polyhedral Pd NCs and their electrocatalytic applications in fuel cells. After a brief introduction to the general NC growth mechanisms and the relationship between their surface structures and shapes, we focus on a variety of shapecontrolled synthesis strategies that have been explored to control the fabrication of polyhedral Pd NCs. This review also examines the applications of Pd NCs to the electrocatalytic oxidation of formic acid, methanol, and ethanol as well as the reduction of O2, with an emphasis on their use in fuel cells. Finally, we outline our personal perspectives on future research directions that are underway with regard to catalytic uses of polyhedral Pd NCs.
Black micro-arc oxide film layers were prepared on AZ40M magnesium alloy substrates by twostep micro-arc oxidation in a phosphate electrolyte with ferric citrate. The morphologies and compositions of these films were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to provide details regarding the film formation mechanism. The results showed that the main component of the oxide films was magnesium oxide, with various iron compounds also being present, including ferroferric oxide, ferrous oxide, and metallic iron. These results indicate that the formation of black film can be attributed to the precipitation of these species during the oxidation of iron ions by ferric citrate in the electrolyte.
Fe3O4/rGO nanocomposites were prepared by hydrothermal method using Fe(OH)3 as precursor of magnetite nanoparticles, graphene oxide (GO) as precursor of reduced graphene oxide (rGO), hydrazine and trisodium citrate as mixed reducing agent. The morphologies, structures and compositions of the products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The electrochemical characteristics of assembled coin-type cells versus metallic lithium were evaluated by cyclic voltammetry and galvanostatic charge-discharge. The uniform morphology, high reductive level of rGO and the role of rGO buffering the volume changes of Fe3O4 nanoparticles in the charging-discharging process can be responsible for the good electrochemical performance of Fe3O4/rGO nanocomposites.
Bipolar interfacial polyelectrolyte membrane fuel cells (BPFCs) are novel devices based on an acidicalkaline bipolar reaction interface. As a result of this innovative bipolar membrane electrode assembly (MEA), BPFCs exhibit outstanding advantages but also present new challenges with regard to the interface. Significant progress has been achieved in BPFCs research in recent years, with the development of key materials and interface technologies. This monograph summarizes the recent advances in MEA technology, including structures, rate-limiting reaction interfaces, water transport mechanisms, and the application of metals other than platinum. These developments in both fundamental theory and primary technologies have established a good foundation for the future research and development of such devices.
In order to explore their luminescence properties, a series of carbon nanodots were prepared by microwave heating by controlling the microwave power, reaction time, and pH value.The luminescence properties of carbon nanodots were characterized by their fluorescence excitation spectrum and emission spectrum.We present the transformation mechanism of glucose into carbon nanodots during the microwave heating process and the corresponding luminescence mechanism together with the analysis of functional group changes during the reaction as monitored with ultraviolet (UV) absorption and Fourier Transform Infrared (FT-IR) spectra.The results show that the optimal luminescence properties of carbon nanodots were obtained when the glucose was heated under a microwave heating power of 560 W for 2.5 min.When the carbon nanodots were excited with UV radiation with a wavelength of 370 nm, the strongest luminescence appeared at 451 nm.The wavelength of the strongest luminescence peak moved from 350 nm to higher wavelengths significantly, when the pH value was modified from acidic to alkaline, and was accompanied with a significant rise in luminescence peak intensity.We show that polycyclic aromatic hydrocarbons form in the reaction process, as evidenced by UV absorption and FTIR monitoring, indicating that microwave synthesis of carbon nanodots proceeds via polymerization and final carbonization of glucose.Carbon nanodots formed under different pH values exhibit a change in the ratio of carbon-to-carbon double bonds to carbon-to-oxygen double bonds.The optical bandgap and exciton binding energy of the carbon nanodots were also investigated comprehensively.
Traditional semiconductor photocatalysts with a wide band gap can achieve visible light responses through element doping. However, the localized levels introduced by impurities may act as recombination centers of charge carriers, which may lower the photocatalytic activity of the doped materials. The solid solution method can realize precise regulation of the band gap and band edge positions of materials to obtain an optimal balance between their optical absorption and redox potentials. The solid solution method is therefore an effective approach to improve the photocatalytic performance of semiconductor materials. In the present review, considering our recent research, we briefly discuss the latest progress of the solid solution method to tune the band gap and band edge positions of photocatalytic materials as well as examining its influence on carrier separation and migration properties. Finally, challenges and prospects for further development of this method are presented.
Two novel ternary rare earth complexes [Ln(3, 4-DEOBA)3DIPY]2DIPY (Ln=Er (1), Gd (2); 3, 4-DEOBA=3, 4-diethoxybenzoate; DIPY=2, 2'-bipyridine) were synthesized and characterized by elemental analysis, infrared spectroscopy and X-ray single crystal diffraction. The experiments show that the two complexes are isomorphous with dinuclear structures, and adjacent structure units are stitched together through π-π interactions to form 1D chains and 2D-layered supramolecular structures. Simultaneous thermal analysis and Fourier transform infrared detection (TG-FTIR) was used to study the process of the thermal decomposition of the complexes. The molar heat capacity of the two complexes was obtained by differential scanning calorimetry (DSC). The smoothed values of the average molar heat capacity and thermodynamic functions of the complexes were calculated by the fitted polynomial and thermodynamic equations.
Sulfated β-cyclodextrin (β-CD) was prepared by the reaction of β-CD with p-toluenesulfonyl chloride at low temperature in aqueous sodium hydroxide. The product was analyzed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). The novel benzil-bridged β-CD (BB β-CD) was acquired by the reaction of benzil with sulfated β-CD at a molar ratio of 1: 2. UV spectrophotometry was used to study the synthetic mechanism of BB β-CD and benzil and their adsorption onto U(VI). Scanning electron microscopy (SEM) was used to analyze the surface properties of the materials. The adsorption of BB β-CD onto U(VI) was investigated as a function of pH, contact time, temperature, and interfering ions using the batch adsorption technique. It was found that the adsorption equilibrium of BB β-CD was reached faster than that of benzil. The optimum experimental conditions were pH=4.5 and shaking for 60 min, achieving the maximum adsorption capacity of 12.16 mg·g-1 and a U(VI) removal ratio of 91.2%. Kinetic studies revealed that the adsorption reached equilibrium within 60 min for U(VI) and followed a pseudo-second-order rate equation. The isothermal data correlated with the Langmuir model better than with the Freundlich model. The thermodynamic data indicated the spontaneous and endothermic nature of the process.
In this article, we used coal-derived carbon foam (CCF) as a skeleton material to encapsulate the solid-to-solid phase change material polyurethane (PU) to provide PU@CCF composites for functional applications. The obtained PU@CCF composites were characterized by field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermal conductivity measurements. The results illustrated that the most preferred ratio of polyethylene glycol (PEG-6000) to hexamethylene diisocyanate (HDI) to synthesize PU was 1:2 and the CCF skeleton prevented PU leakage during the phase change process. Compared with PEG-6000, the thermal conductivity of the PU@CCF composite was raised by 54%, its cycle thermal stability was remarkable after 2000 cycles, and its supercooling degree was lowered by more than 10℃. For electro-to-heat energy conversion, the phase transition behavior of the obtained PU@CCF could be induced under an electron voltage as low as 0.8 V with 75% conversion efficiency at 1.1 V. This functional phase change composite realizes electric-heat conversion under the lowest loading voltage reported to date, providing an important benchmark for the preparation and functionalization of low-cost phase change composites.
Although a large variety of aromatic systems have been unveiled in the literature, justifying their origin of stability and understanding their nature of aromaticity is still an unaccomplished task. In this work, using tools recently developed by us within the density functional reactivity theory framework, where we employ simple density functionals to quantify molecular structural and reactivity properties, we examine the aromaticity concept from a different perspective. Using six quantities from the information-theoretic approach, namely, the Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy, Onicescu information energy, information gain, and relative Rényi entropy, and four aromaticity descriptors, namely, the aromatic stabilization energy (ASE) index, the harmonic oscillator model of aromaticity (HOMA) index, the aromatic fluctuation (FLU) index, and the nucleus-independent chemical shift (NICS) index, we systematically examined the correlations between substituted fulvene derivatives fused with one, two, and three benzene rings. Among the 14 benzofulvene derivatives studied in this work, there were seven single-fused, four double-fused, and three triple-fused benzofulvene derivatives. Our results show that the aromaticity indexes are often well correlated with one another. The same is true for information-theoretic quantities. Moreover, these correlations are valid across all series of benzofulvene derivatives with different ring structures. The cross-correlations between information-theoretic quantities and aromaticity indexes were usually strong. However, two completely opposite patterns were observed; as a consequence, these correlations are not valid across all series of benzofulvene derivatives. The nature of these correlations depends on the nature of the ring structure. The two groups of systems, each obeying the same cross-correlation patterns, have a total number of 4n + 2 and 4n π electrons, respectively, which are in agreement with Hückel's rule of aromaticity and antiaromaticity. Compared with the results obtained for systems without a benzene fused ring, the correlation patterns of these quantities were always found to be the same, both with and without fused benzene rings. This suggests that, despite benzene's aromaticity, its fusion with a fulvene moiety does not modify the aromaticity and antiaromaticity of the fulvene ring. These results confirm that the fusion of benzene rings with a fulvene moiety has no influence on the aromatic nature of the fulvene moiety. Thus, the aromaticity and antiaromaticity of benzene-fused fulvene derivatives are solely determined by the fulvene moiety. These results should provide a new understanding of the origin and nature of aromaticity and antiaromaticity.
Two-dimensional layered zeolite precursors (LZPs) with layered structural units of parent threedimensional zeolites possess the properties of the parent materials but with an open framework structure. The structural properties of these materials therefore provide new opportunities to synthesize new zeolites and fabricate sub-zeolites with distinct structures, making them a hot topic in zeolite research. Enormous LZPs were synthesized by the direct crystallization or post-modification of their three-dimensional parent structures. Several layer manipulation strategies, including swelling, delamination, pillaring and layer reassembly have been developed on two-dimensional LZPs. These strategies have provided access to zeolites with new structures as well as materials even violating the theoretical rules, which have greatly enhanced the field of two-dimensional LZPs, and expanded their applications in catalysis and separation. Herein, we have reviewed the structural characteristics of two-dimensional LZPs, as well as summarizing their syntheses, modifications, and catalytic applications. We have also proposed the future perspectives of two-dimensional LZPs.
Structure transformation and neck growth during the heat and sintering process of two TiO2 nanoparticles were investigated using molecular dynamics (MD) simulations. Based on the space meshing of the system and analysis of neighboring meshes, a neck atom identification model was developed. The model was successfully applied to identify neck atoms. Combined with the surface atom identification model previously developed by the authors, atoms in the system were further classified and the characteristics of the classified atoms were simulated and analyzed. The results show that sintering occurs when the temperature is above 573 K, the neck area increases with increasing sintering temperature, and it is mostly occupied by interior atoms. Surface atoms occupy less neck area and they are less sensitive to sintering temperature variation. The average displacement of neck atoms is larger than that of surface and interior atoms of the mother particles and O atoms are more active in migration than Ti atoms in the neck. Meanwhile, displacement of outside neck atoms is larger than that of inside neck atoms, meaning that neck growth mainly depends on the motion of outside neck atoms. The proposed model is stable and effective, and it provides fundamental information to analyze nanostructures in different zones.
Understanding the nature of the active sites and the relationship between the catalyst structure and its performance are fundamental aspects of heterogeneous catalysis. With the development of modern surface science techniques, atomically resolved surface structures of heterogeneous catalysts and their properties can be studied with ease. Combined with an in situ high pressure cell, model catalysis studies can provide convincing information about the relationship between the catalyst structure and its performance. In this mini-review, several case studies of model catalysts have been summarized, including those of the active surfaces for CO and alkane oxidation using the Pt group metals as catalysts, the active site of gold nanoparticles for CO oxidation, synergistic effects between VOx and Pt for propane oxidation, promotional effects of Au in Pd-Au catalysts for vinyl acetate synthesis, structure-sensitivity of n-heptane dehydrocyclization on model oxide-supported Pt, as well as several significant improvements of the model catalysis techniques.
This study used the target-controlled anodizing process for the controllable fabrication of TiO2 nanotube arrays (TiO2 NTAs) film substrate with large specific surface area and well-separated nanotubes. After annealing crystallization, TiO2 NTAs were successively functional modified by electrochemical hydrogenation and sequential chemical bath deposition of high specific capacitance MnO2 nanoparticles onto both the outer and inner surfaces of the nanotubes, thus constructing the heterostructured MnO2/H-TiO2 NTAs electrode. The as-prepared samples were fully characterized by field emission scanning electron microscopy (FESEM), highresolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy. The supercapacitive performance and stability of the resulting samples were systematically evaluated using electrochemical workstation. The results from the current study revealed that conductivity and electrochemical properties of H-TiO2 NTAs were dramatically enhanced through electrochemical hydrogenation and the specific capacitance of H-TiO2 NTAs could achieve 7.5 mF·cm-2 at current density of 0.2 mA·cm-2, which is almost 75 times the performance of TiO2 NTAs (0.1 mF·cm-2). Furthermore, the specific capacitance of MnO2/H-TiO2 NTAs-2 could achieve 481.26 F·g-1 at a current density of 3 mA·mg-1 as well as outstanding long-term cycling stability with only 11% reduction of initial specific capacitance at a current density of 5 mA·mg-1 after 1000 cycles.
The aprotic Li-O2 battery has attracted considerable interest in recent years because of its high theoretical specific energy that is far greater than that achievable with state-of-the-art Li-ion technologies. To date, most Li-O2 studies, based on a cell configuration with a Li metal anode, aprotic Li+ electrolyte and porous O2 cathode, have focused on O2 reactions at the cathode. However, these reactions might be complicated by the use of Li metal anode. This is because both the electrolyte and O2 (from cathode) can react with the Li metal and some parasitic products could cross over to the cathode and interfere with the O2 reactions occurring therein. In addition, the possibility of dendrite formation on the Li anode, during its multiple plating/stripping cycles, raises serious safety concerns that impede the realization of practical Li-O2 cells. Therefore, solutions to these issues are urgently needed to achieve a reversible and safety Li anode. This review summarizes recent advances in this field and strategies for achieving high performance Li anode for use in aprotic Li-O2 batteries. Topics include alternative counter/reference electrodes, electrolytes and additives, composite protection layers and separators, and advanced experimental techniques for studying the Li anode|electrolyte interface. Future developments in relation to Li anode for aprotic Li-O2 batteries are also discussed.
3C-like protease is an extremely important protease involved in the multiplicative process of coronaviruses, including the deadlyMiddle East respiratory syndrome coronavirus (MERS-CoV). 3C-like protease has become a hot research topic in the field of coronavirology. For the first time, a set of ligand-and receptorbased three-dimensional quantitative structure-activity relationships (3D-QSAR) models were carried out via comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) to explore the structure-activity correlation of 43 peptidomimetic inhibitors of the 3C-like protease of the bat coronavirus HKU4 (HKU4-CoV), which belongs to the same 2c lineage as MERS-CoV and shows high sequence similarity with MERS-CoV. Based on the ligand-based alignment, an optimal CoMSIAmodel (yielded by steric, electrostatic, H-bond donor and H-bond acceptor fields) was obtained with good predictive power of Q2=0.522, R2 ncv=0.996 and R2 pre=0.904 (Q2:cross-validated correlation coefficient, R2 ncv:non-cross-validated correlation coefficient, R2 pre:predicted correlation coefficient for the test set of compounds). Molecular docking and molecular dynamics simulations were performed according to this model to further determine the interaction mechanism between ligands and the receptor. The experimental results show:(1) based on the optimal CoMSIAmodel, the 3D contour maps vividly illustrate that the molecular biological activity is influenced by the steric, electrostatic, H-bond donor and H-bond acceptor interactions of molecular groups. (2) Based on the docking analysis, hydrophobicity, crystal water, His166 andGlu169 have important roles in the ligands and receptor binding process. (3) Molecular dynamics (MD) simulations were carried out for further verification of the reliability of the docking model, and provide two new key residues, Ser24 and Gln192, which have two strong hydrogen bonds with the ligands. Some new compounds were obtained based on the modeling that are potential peptidomimetic inhibitors of 3C-like protease. These results help establish the binding mechanism between 3C-like protease and peptidomimetic inhibitors, and provide a valuable reference for future anti-MERS-CoV drug design.
The excited-state properties of two-dimensional carbon nitrides, including triazine and tri-s-triazine, were investigated using many-body Green's function theory. Their quasiparticle energies were calculated with the GW method. By solving the Bethe-Salpeter equation (BSE), which takes into account electron-hole interactions, excitation energies and optical spectra were obtained. Strong interactions, mainly originating from exchange interactions, were found between σ and π orbitals in the valence bands of the two carbon nitrides. The quasiparticle corrections for occupied σ and π orbitals are quite different, so both of them need to be calculated at the level of the GWmethod to obtain accurate results for both band gaps and optical spectra from the BSE. Compared with monolayer carbon nitrides, interlayer van der Waals interactions in bilayer systems lower the band gap by 0.6 eV, while the optical absorption spectrum red shifts by 0.2 eV. This is because of the smaller exciton binding energy in bilayer systems. Our calculated positions of the absorption peaks are in good agreement with experiments. The absorption peaks in experiments are dominated by transitions from deep π orbitals to π* orbitals. Coupling between π→π* and σ→π* transitions can lead to a weak absorption tail in the long wavelength region. If we tune the polarization direction of the incident light, new strong absorption peaks originating from σ→π* transitions emerge at lower energies.
In this paper, we develop a surface atom identification model to perform atom identification and analysis of the surface atoms of a single TiO2 nanoparticle during the heating and sintering process. Cubic mesh was used to obtain the particle structure mesh, and the optimal mesh size of 0.3 nm was determined by volumetric integration of a spherical particle. Surface atoms were classified according to identification of surface meshes, and the number of external meshes in all of the neighbor meshes (Next) was set as a criterion to determine whether the target mesh was a surface mesh. The optimal value was Next=9. LAMMPS was used to simulate the heating process of a particle with a radius of 0.75 nm. The results show that energy relaxation is significantly faster than structure relaxation. The atom classification analysis with the developed surface atom identification model shows that displacement of the surface atoms is larger than the interior atoms, and surface O atoms are more active in migration than surface Ti atoms. The coordination number of surface atoms is lower than that of interior atoms. The present study provides fundamental information for analyzing the active structure distribution of nanoparticles.
Inorganic porous materials have been widely applied in the field of chemical industry, energy, environmental protection and other fields owing to their special physicochemical properties. In this paper, the current research progress on inorganic porous materials was summarized. The detailed preparation methods for macroporous, mesoporous, microporous materials and macro-mesoporous, macro-microporous, meso-microporous, macro-meso-microporous materials have been discussed in detail. The indoor and outdoor applications of inorganic porous materials for environmental protection were described and the application of inorganic porous materials in the field of removing mobile source pollution was particularly introduced. Finally, the existing problems about the preparation of inorganic porous materials were summarized and the future research directions for the preparation and application of inorganic porous materials were also prospected.
With solar, wind, and other types of renewable energy incorporated into electrical grids and with the construction of smart grids, energy storage technology has become essential to optimize energy utilization. Due primarily to its abundance and low cost, aqueous rechargeable sodium-ion batteries (ARSBs) have received increasing attention in the field of electrochemical energy storage technology, and represent a promising alternative to energy storage in future power grids. However, because of the limitations of the thermodynamics of electrochemical processes in water, reactions in aqueous solution are more complicated compared to an organic system. Many parameters must be taken into account in an aqueous system, such as electrolyte concentration, dissolved oxygen content, and pH. As a result, it is challenging to select an appropriate electrode material, whose capacity, electrochemical potential, adaptability, and even catalytic effect may seriously affect the battery performance and hamper its application. Therefore, the development of advanced electrode materials, which can suppress side reactions of the battery and have good electrochemical performance, has become the focus of ARSB research. This paper briefly discusses the characteristics of ARSBs and summarizes the latest research progress in the development of electrode materials, including oxides, polyanionic compounds, Prussian blue analogues, and organics. This review also discusses the challenges remaining in the development of ARSBs, and suggests several ways to solve them, such as by using multivalent ions, hybridized electrolytes, etc., and speculates about future research directions. The studies and concepts discussed herein will advance the development of ARSBs and promote the optimization of energy utilization.