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Showing papers in "Journal of Materials Chemistry in 2015"


Journal ArticleDOI
TL;DR: In this paper, a critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics).
Abstract: There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

1,489 citations


Journal ArticleDOI
TL;DR: In this paper, a review summarizes recent studies of the relationship of the chemical stability of perovskite solar cells with their environment (oxygen and moisture, UV light, solution process, temperature) and corresponding possible solutions.
Abstract: In recent years, the record efficiency of perovskite solar cells (PSCs) has been updated from 9.7% to 20.1%. However, there has been very little study of the issue of stability, which restricts the outdoor application of PSCs. The issues of the degradation of perovskite and the stability of PSC devices should be urgently addressed to achieve good reproducibility and long lifetimes for PSCs with high conversion efficiency. Without studies on stability, exciting achievements cannot be transferred from the laboratory to industry and outdoor applications. In order to improve their stability, a basic understanding of the degradation process of PSCs in different conditions should be acquired via thorough study. This review summarizes recent studies of the relationship of the chemical stability of PSCs with their environment (oxygen and moisture, UV light, solution process, temperature) and corresponding possible solutions.

1,442 citations


Journal ArticleDOI
TL;DR: In this article, a review of the recent developments and issues concerning polyethylene oxide (PEO) based electrolytes for lithium-ion batteries is presented, including blending, modifying and making PEO derivatives.
Abstract: Poly(ethylene oxide) (PEO) based materials are widely considered as promising candidates of polymer hosts in solid-state electrolytes for high energy density secondary lithium batteries. They have several specific advantages such as high safety, easy fabrication, low cost, high energy density, good electrochemical stability, and excellent compatibility with lithium salts. However, the typical linear PEO does not meet the production requirement because of its insufficient ionic conductivity due to the high crystallinity of the ethylene oxide (EO) chains, which can restrain the ionic transition due to the stiff structure especially at low temperature. Scientists have explored different approaches to reduce the crystallinity and hence to improve the ionic conductivity of PEO-based electrolytes, including blending, modifying and making PEO derivatives. This review is focused on surveying the recent developments and issues concerning PEO-based electrolytes for lithium-ion batteries.

1,414 citations


Journal ArticleDOI
TL;DR: In this paper, the authors showed that the organic cation is not essential, but simply a convenience for forming lead triiodide perovskites with good photovoltaic properties.
Abstract: The vast majority of perovskite solar cell research has focused on organic–inorganic lead trihalide perovskites. Herein, we present working inorganic CsPbI3 perovskite solar cells for the first time. CsPbI3 normally resides in a yellow non-perovskite phase at room temperature, but by careful processing control and development of a low-temperature phase transition route we have stabilised the material in the black perovskite phase at room temperature. As such, we have fabricated solar cell devices in a variety of architectures, with current–voltage curve measured efficiency up to 2.9% for a planar heterojunction architecture, and stabilised power conversion efficiency of 1.7%. The well-functioning planar junction devices demonstrate long-range electron and hole transport in this material. Importantly, this work identifies that the organic cation is not essential, but simply a convenience for forming lead triiodide perovskites with good photovoltaic properties. We additionally observe significant rate-dependent current–voltage hysteresis in CsPbI3 devices, despite the absence of the organic polar molecule previously thought to be a candidate for inducing hysteresis via ferroelectric polarisation. Due to its space group, CsPbI3 cannot be a ferroelectric material, and thus we can conclude that ferroelectricity is not required to explain current–voltage hysteresis in perovskite solar cells. Our report of working inorganic perovskite solar cells paves the way for further developments likely to lead to much more thermally stable perovskite solar cells and other optoelectronic devices.

1,304 citations


Journal ArticleDOI
TL;DR: In this paper, the authors highlight the recent progress on mechanical exfoliation for graphene production during the last decade, focusing on the widely used sonication method with the latest insight into sonication-induced defects, newly explored ball milling method, the fluid dynamics method that has emerged in the last three years, and the innovative supercritical fluid method.
Abstract: Mass production and commercial availability are prerequisites for the viability and wide application of graphene. The exfoliation of graphite to give graphene is one of the most promising ways to achieve large-scale production at an extremely low cost. This review focuses on discussing different exfoliation techniques based on a common mechanical mechanism; because a deep understanding of the exfoliation mechanism can provide fruitful information on how to efficiently achieve high-quality graphene by optimizing exfoliation techniques. We highlight the recent progress on mechanical exfoliation for graphene production during the last decade. The emphasis is set on the widely used sonication method with the latest insight into sonication-induced defects, the newly explored ball milling method, the fluid dynamics method that has emerged in the last three years, and the innovative supercritical fluid method. We also give an outlook on how to achieve high-quality graphene efficiently using mechanical exfoliation techniques. We hope this review will point towards a rational direction for the scalable production of graphene.

1,178 citations


Journal ArticleDOI
TL;DR: In this article, the structural, electrical, and optical properties of halide perovskite materials in relation to their applications in solar cells are summarized and discussed, along with possible theoretical solutions.
Abstract: 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 19.3% in 2014, by using the all-solid-state thin-film architecture and engineering cell structures with mixed-halide perovskites. The emergence of perovskite solar cells revolutionized the field not only because of their rapidly increased efficiency, but also 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 relation to their applications in solar cells. We also discuss some current challenges of using perovskites in solar cells, along with possible theoretical solutions.

1,066 citations


Journal ArticleDOI
TL;DR: In this paper, the degradation mechanism of planar-structured CH3NH3PbI3 perovskite solar cells (PSCs) was investigated under various simulated environmental conditions.
Abstract: The stability of encapsulated planar-structured CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSCs) was investigated under various simulated environmental conditions. The tests were performed under approximately one sun (100 mW cm−2) illumination, varying temperature (up to 85 °C cell temperature) and humidity (up to 80%). The application of advanced sealing techniques improved the device stability, but all devices showed significant degradation after prolonged aging at high temperature and humidity. The degradation mechanism was studied by post-mortem analysis of the disassembled cells using SEM and XRD. This revealed that the degradation was mainly due to the decomposition of MAPbI3, as a result of reaction with H2O, and the subsequent reaction of hydroiodic acid, formed during MAPbI3 decomposition, with the silver back contact electrode layer.

866 citations


Journal ArticleDOI
TL;DR: A comprehensive overview of the recent developments of heterogeneous electrocatalysts for the hydrogen evolution reaction is presented in this paper, where the challenges and solutions for further improving their performance are discussed.
Abstract: The hydrogen evolution reaction plays a decisive role in a range of electrochemical and photoelectrochemical devices. It requires efficient and robust electrocatalysts to lower the reaction overpotential and minimize energy consumption. Over the last decade, we have witnessed a rapid rise in new electrocatalysts, particularly those based on non-precious metals. Some of them approach the activity of precious metal benchmarks. Here, we present a comprehensive overview of the recent developments of heterogeneous electrocatalysts for the hydrogen evolution reaction. Detailed discussion is organized from precious metals to non-precious metal compounds including alloys, chalcogenides, carbides, nitrides, borides and phosphides, and finally to metal-free materials. Emphasis is placed on the challenges facing these electrocatalysts and solutions for further improving their performance. We conclude with a perspective on the development of future HER electrocatalysts.

845 citations


Journal ArticleDOI
TL;DR: In this paper, a binary g-C3N4/ZnO photocatalytic system was constructed via a one-step facile calcination method and further used as a photocatalyst for CO2 reduction.
Abstract: Photocatalytic CO2 reduction into renewable hydrocarbon solar fuels is considered as a promising strategy to simultaneously address the global energy and environmental issues. In this study, a binary g-C3N4/ZnO photocatalytic system was constructed via a one-step facile calcination method and further used as a photocatalyst for CO2 reduction. It was shown that the as-prepared g-C3N4/ZnO photocatalytic system exhibited enhanced photocatalytic activity for CO2 reduction by a factor of 2.3 compared with pure g-C3N4, while maintaining the original selectivity of pure g-C3N4 to convert CO2 directly into CH3OH. For the first time, the coupling effect of ZnO responsible for the improved photoactivity of g-C3N4 was fully illustrated and a direct Z-scheme mechanism rather than the conventional heterojunction-type mechanism was proposed to explain the better performances of the g-C3N4/ZnO binary composite photocatalytic system. The enhancement of photocatalytic CO2 reduction activity is attributed to the highly efficient ZnO-to-g-C3N4 electron transfer occurring at the intimate contact interface between the g-C3N4 phase and ZnO phase. This work will provide new deep insights into the rational construction of a g-C3N4-based photocatalytic system and the design of a direct Z-scheme system without an electron mediator for photocatalytic CO2 reduction reactions.

767 citations


Journal ArticleDOI
TL;DR: MnO2-based materials have been intensively investigated for use in pseudocapacitors due to their high theoretical specific capacitance, good chemical and thermal stability, natural abundance, environmental benignity and low cost as mentioned in this paper.
Abstract: MnO2-based materials have been intensively investigated for use in pseudocapacitors due to their high theoretical specific capacitance, good chemical and thermal stability, natural abundance, environmental benignity and low cost. In this review, several main factors that affect the electrochemical properties of MnO2-based electrodes are presented. Various strategic design and synthetic methods of MnO2-based electrode materials for enhanced electrochemical performance are highlighted and summarized. Finally, the challenges and future directions toward the development of MnO2-based nanostructured electrode materials for high performance supercapacitors (SCs) are discussed.

750 citations


Journal ArticleDOI
TL;DR: In this paper, a computational screening based on density-functional-theory calculations reveals Ge as a candidate element for replacing Pb in halide perovskite compounds suitable for light harvesting.
Abstract: Computational screening based on density-functional-theory calculations reveals Ge as a candidate element for replacing Pb in halide perovskite compounds suitable for light harvesting. Experimentally, three AGeI3 (A = Cs, CH3NH3 or HC(NH2)2) halide perovskite materials have been synthesized. These compounds are stable up to 150 °C, and have bandgaps correlated with the A-site cation size. CsGeI3-based solar cells display higher photocurrents, of about 6 mA cm−2, but are limited by poor film forming abilities and oxidising tendencies. The present results demonstrate the utility of combining computational screening and experimental efforts to develop lead-free halide perovskite compounds for photovoltaic applications.

Journal ArticleDOI
TL;DR: In this article, a review of the recent developments of anode materials on the nanoscale is presented, focusing on the fabrication of the nanostructured anode owing to its special properties, such as high surface area, short Li+ ion diffusion path length, high electron transportation rate etc.
Abstract: High-energy consumption in our day-to-day life can be balanced not only by harvesting pollution-free renewable energy sources, but also requires proper storage and distribution of energy. In this regard, lithium ion batteries are currently considered as effective energy storage devices and involve the most active research. There exist several review articles dealing with various sections of LIBs, such as the anode, the cathode, electrolytes, electrode–electrolyte interface etc. However, the anode is considered to be a crucial component affecting the performance of LIBs as evident from the tremendous amount of current research work carried out in this area. In the last few years, advancements have been focused more on the fabrication of the nanostructured anode owing to its special properties, such as high surface area, short Li+ ion diffusion path length, high electron transportation rate etc. As the work in this area is growing very fast, the present review paper deliberates the recent developments of anode materials on the nanoscale. Different types of anode materials, such as carbon-based materials, alloys, Si-based materials, transition metal oxides, and transition metal chalcogenides, with their unique physical and electrochemical properties, are discussed. Various approaches to designing materials in the form of 0, 1 and 2D nanostructures and their effect of size and morphology on their performance as anode materials in LIBs are reviewed. Moreover, the article emphasizes smart approaches for making core–shell particles, nanoheterostructures, nanocomposites or nanohybrids with the combination of electrochemically active materials and conductive carbonaceous or electrochemically inactive materials to achieve LIBs with high capacity, high rate capability, and excellent cycling stability. We believe the review paper will provide an update for the reader regarding recent progress on nanostructured anode materials for LIBs.

Journal ArticleDOI
TL;DR: For selected candidates, the energy density at the automotive battery cell level for electric vehicle applications is calculated using an in-house developed software and literature results concerning their power capability and lifetime are discussed with reference to the automotive targets.
Abstract: Future generations of electrified vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium batteries is mandatory, maintaining at the same time similar, or improved, rate capability, lifetime, cost, and safety. Several new cathode materials have been claimed over the last decade to allow for this energy improvement. The possibility that some of them will find application in the future automotive batteries is critically evaluated here by first considering their theoretical and experimentally demonstrated energy densities at the material level. For selected candidates, the energy density at the automotive battery cell level for electric vehicle applications is calculated using an in-house developed software. For the selected cathodes, literature results concerning their power capability and lifetime are also discussed with reference to the automotive targets.

Journal ArticleDOI
TL;DR: In this article, a cubic framework of amorphous carbon and uniformly dispersed core-shell Fe@graphitic carbon nanoparticles is used to construct a high-performance microwave absorber.
Abstract: Composites of magnetic metal nanoparticles and carbon materials are highly desirable for high-performance microwave absorbers due to their compatible dielectric loss and magnetic loss abilities. In this article, novel nanocomposites, Fe/C nanocubes, have been successfully prepared through an in situ route from a metal–organic framework, Prussian blue, by controlled high-temperature pyrolysis. The resultant nanocubes are actually composed of a cubic framework of amorphous carbon and uniformly dispersed core–shell Fe@graphitic carbon nanoparticles. Within the studied pyrolysis temperature range (600–700 °C), the porous structure, iron content, magnetic properties, and graphitization degree of the Fe/C nanocubes can be well modulated. Particularly, the improved carbon graphitization degree, both in amorphous frameworks and graphitic shells, results in enhanced complex permittivity and dielectric loss properties. The homogeneous chemical composition and microstructure stimulate the formation of multiple dielectric resonances by regularizing various polarizations. The synergistic effect of dielectric loss, magnetic loss, matched impedance, and dielectric resonances accounts for the improved microwave absorption properties of the Fe/C nanocubes. The absorption bands of the optimum one obtained at 650 °C are superior to most composites ever reported. By considering the good chemical homogeneity and microwave absorption, we believe that the as-fabricated Fe/C nanocubes will be promising candidates as highly effective microwave absorbers.

Journal ArticleDOI
TL;DR: In this paper, a comparison of the material selection for various layers as well as their corresponding impact on the perovskite film and device behavior in both device architectures is presented.
Abstract: Organic–inorganic metal halide perovskites have recently shown great potential for application in solar cells with excitingly high performances with an up-to-date NREL-certified record efficiency of 20.1%. This family of materials has demonstrated considerable prospects in achieving efficiencies comparable to or even better than those of thin film solar cells. The remarkable performances thus far seem not to be limited to any specific device architecture. Both mesoscopic and planar cells showed good device performance and this eventually leads to the inevitable comparison between both architectures. Regardless of device architecture, device performance is highly dependent on the film morphology. The factors influencing the film morphology such as the deposition method, material composition, additives and film treatment will be discussed extensively in this review. The key to obtaining good-quality film morphology and hence performance is to essentially lower the energy barrier for nucleation and to promote uniform growth of the perovskite crystals. A comparison of the material selection for various layers as well as their corresponding impact on the perovskite film and device behavior in both device architectures will be presented.

Journal ArticleDOI
TL;DR: The vanadium redox flow battery as mentioned in this paper is an electrochemical storage system which allows energy to be stored in two solutions containing different redox couples, and it has been proven to be an economically attractive and low-maintenance solution, with significant benefits over the other types of batteries.
Abstract: The vanadium redox flow battery, which was first suggested by Skyllas-Kazacos and co-workers in 1985, is an electrochemical storage system which allows energy to be stored in two solutions containing different redox couples. Unlike commercially available batteries, all vanadium redox flow batteries have unique configurations, determined by the size of the electrolyte tanks. This technology has been proven to be an economically attractive and low-maintenance solution, with significant benefits over the other types of batteries. Moreover, the soaring demand for large-scale energy storage has, in turn, increased demands for unlimited capacity, design flexibility, and good safety systems. This work reviews and discusses the progress on electrodes and their reaction mechanisms as key components of the vanadium redox flow battery over the past 30 years. In terms of future outlook, we also provide practical guidelines for the further development of self-sustaining electrodes for vanadium redox flow batteries as an attractive energy storage system.

Journal ArticleDOI
TL;DR: In this article, the authors discuss the current development of graphene-based metal and metal oxide nanocomposites, with a detailed account of their synthesis and properties, including their applications in various fields including electronics, electrochemical and electrical fields.
Abstract: Graphene, an atomically thin two-dimensional carbonaceous material, has attracted tremendous attention in the scientific community, due to its exceptional electronic, electrical, and mechanical properties. Indeed, with the recent explosion of methods for a large-scale synthesis of graphene, the number of publications related to graphene and other graphene based materials has increased exponentially. Particularly the development of easy preparation methods for graphene like materials, such as highly reduced graphene oxide (HRG) via reduction of graphite oxide (GO), offers a wide range of possibilities for the preparation of graphene based inorganic nanocomposites by the incorporation of various functional nanomaterials for a variety of applications. In this review, we discuss the current development of graphene based metal and metal oxide nanocomposites, with a detailed account of their synthesis and properties. Specifically, much attention has been given to their wide range of applications in various fields, including electronics, electrochemical and electrical fields. Overall, by the inclusion of various references, this review covers in detail the aspects of graphene-based inorganic nanocomposites.

Journal ArticleDOI
TL;DR: Sulfur-doped carbon dots were synthesized using a simple and straightforward hydrothermal method in this article, and as-prepared S-Doped C-dots exhibit significant fluorescence quantum yield (67%) and unique emission behavior.
Abstract: Sulfur-doped carbon dots (S-doped C-dots)were synthesized using a simple and straightforward hydrothermal method. The as-prepared S-doped C-dots exhibit significant fluorescence quantum yield (67%) and unique emission behavior. The spherical S-doped C-dots have an average diameter of 4.6 nm and the fluorescence of S-doped C-dots can be effectively and selectively quenched by Fe3+ ions. Thus, S-doped C-dots were applied as probes toward Fe3+ detection, exhibiting a limit of detection of 0.1 μM.

Journal ArticleDOI
TL;DR: Dias et al. as discussed by the authors reviewed the recent advances in the field of organic pollutants removal and degradation and proposed metal-organic frameworks for water reuse, and the next steps in this field.
Abstract: Correction for ‘Towards the use of metal–organic frameworks for water reuse: a review of the recent advances in the field of organic pollutants removal and degradation and the next steps in the field’ by Elton M. Dias et al., J. Mater. Chem. A, 2015, 3, 22484–22506.

Journal ArticleDOI
TL;DR: In this article, the phase of the as-synthesized nickel phosphide nanocrystals (NCs) with different phases (Ni12P5, Ni2P and Ni5P4) were synthesized via the thermal decomposition approach using nickel acetylacetonate as the nickel source, trioctylphosphine as the phosphorus source and oleylamine in 1-octadecene as reductant.
Abstract: Monodispersed nickel phosphide nanocrystals (NCs) with different phases (Ni12P5, Ni2P and Ni5P4) were synthesized via the thermal decomposition approach using nickel acetylacetonate as the nickel source, trioctylphosphine as the phosphorus source and oleylamine in 1-octadecene as the reductant. The phases of the as-synthesized nickel phosphide NCs could easily be controlled by changing the P : Ni precursor ratio. The structure and morphology of the as-synthesized nickel phosphide NCs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and N2 adsorption–desorption. A formation mechanism for the as-synthesized nickel phosphide NCs was proposed. We further studied the influence of the phase of the nickel phosphide NCs on the electrocatalytic properties for the hydrogen evolution reaction (HER). All phases showed good catalytic properties, and the Ni5P4 NCs with a solid structure exhibited higher catalytic activity than the Ni12P5 and Ni2P NCs. This superior catalytic activity is attributed to the higher positive charge of Ni and a stronger ensemble effect of P in Ni5P4 NCs. This study demonstrates that the crystalline phase is important for affecting the electrocatalytic properties.

Journal ArticleDOI
TL;DR: In this paper, the authors summarized the recent advancements made, also covering the prospective materials for both the battery cathode and anode, and opinions on possible solutions through correlating trends in recent papers will be suggested.
Abstract: The rapid consumption of non-renewable resources has resulted in an ever-increasing problem of CO2 emissions that has motivated people for investigating the harvesting of energy from renewable alternatives (e.g. solar and wind). Efficient electrochemical energy storage devices play a crucial role in storing harvested energies in our daily lives. For example, rechargeable batteries can store energy generated by solar cells during the daytime and release it during night-time. In particular, lithium-ion batteries (LIBs) have received considerable attention ever since their early commercialization in 1990s. However, with initiatives by several governments to build large-scale energy grids to store energy for cities, problems such as the high cost and limited availability of lithium starts to become major issues. Sodium, which also belongs to Group 1 of the periodic table, has comparable electrochemical properties to Lithium, and more importantly it is considerably more accessible than lithium. Nonetheless, research into sodium-ion batteries (NIBs) is currently still in its infancy compared to LIBs, although great leaps and bounds have been made recently in terms of research and development into this technology. Here in this review, we summarize the recent advancements made, also covering the prospective materials for both the battery cathode and anode. Additionally, opinions on possible solutions through correlating trends in recent papers will be suggested.

Journal ArticleDOI
TL;DR: In this paper, the authors present an extensive description of binary transition metal oxides (BTMO) materials and the most commonly used synthetic methods for supercapacitors and review several notable BTMOs and their composites in application of supercapACitors.
Abstract: Binary transition metal oxides (BTMOs) possess higher reversible capacity, better structural stability and electronic conductivity, and have been widely studied to be novel electrode materials for supercapacitors. In this review, we present an extensive description of BTMO materials and the most commonly used synthetic methods. Furthermore, we review several notable BTMOs and their composites in application of supercapacitors. With the increasing attention for energy storage, more and more exciting results about BTMO materials will be reported in the future.

Journal ArticleDOI
TL;DR: A review of the various electrolytes currently used and developed for SIBs, both in terms of materials and concepts, is presented in this paper, where the rationale for specific choices made, salts, solvents, additives, concentrations, etc.
Abstract: The first review of the various electrolytes currently used and developed for sodium-ion batteries (SIBs), both in terms of materials and concepts, is presented. In contrast to the Li-ion battery (LIB), which is a mature technology for which a more or less unanimously accepted “standard electrolyte” exists: 1 M LiPF6 in EC/DMC, the electrolyte of choice for SIBs has not yet fully conformed to a standard. This is true for both materials: salts, solvents, or additives, and concept, using the main track of organic solvents or aiming for other concepts. SIB research currently prospers, benefitting from using know-how gained from 30 years of LIB R&D. Here the currently employed electrolytes are emphasized and their effects on practical SIB performance are outlined, scrutinizing the rationale for specific choices made, salts, solvents, additives, concentrations, etc. for each specific cell set-up and usage conditions.

Journal ArticleDOI
TL;DR: In this article, the maximum reflection loss of FeCo/graphene hybrids reaches −40.2 dB at 8.9 GHz with a matching thickness of only 2.5 mm, and the absorption bandwidth with reflection loss exceeding −10 dB is in the 3.4-18 GHz range for the absorber thickness of 1.5-5 mm.
Abstract: CoFe2O4/graphene oxide hybrids have been successfully fabricated via a facile one-pot polyol route, followed by chemical conversion into FeCo/graphene hybrids under H2/NH3 atmosphere. These magnetic nanocrystals were uniformly decorated on the entire graphene nanosheets without aggregation. The morphology, chemical composition and crystal structure have been characterized in detail. In particular, FeCo/graphene hybrids show significant improvement in both permeability and permittivity due to the combination of the high magnetocrystalline anisotropy of metallic FeCo and high conductivity of light-weight graphene. This leads to remarkable enhancement in microwave absorption properties. The maximum reflection loss of FeCo/graphene hybrids reaches −40.2 dB at 8.9 GHz with a matching thickness of only 2.5 mm, and the absorption bandwidth with reflection loss exceeding −10 dB is in the 3.4–18 GHz range for the absorber thickness of only 1.5–5 mm. Moreover, the experimental relationship between matching thickness and frequency is found to obey the quarter-wavelength matching model, facilitating the design of FeCo/graphene hybrid film for practical application. The results suggest that the FeCo/graphene hybrids developed here can serve as an ideal candidate for the manufacture of light-weight and high-efficiency microwave-absorbing devices.

Journal ArticleDOI
TL;DR: In this paper, a plausible mechanism for the formation of hollow architectures related to Ostwald ripening was proposed, and the results indicated that the microwave absorption properties of flower-like CuS hollow microspheres possess the advantages of broad bandwidth, strong absorption, lightweight and thin thickness.
Abstract: Flower-like CuS hollow microspheres composed of nanoflakes have been successfully prepared via a facile solvothermal method. The crystal structure, morphology and microwave absorption properties of the as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and a network analyser. The effects of reaction temperature, concentration of the reagents and reaction time on the structures and morphologies of the CuS products were investigated using XRD and SEM techniques. A plausible mechanism for the formation of hollow architectures related to Ostwald ripening was proposed. The CuS/paraffin composite containing 30 wt% CuS hollow microspheres shows the best microwave absorption properties compared with other CuS/paraffin composites. The minimum reflection loss of −31.5 dB can be observed at 16.7 GHz and reflection loss below −10 dB is 3.6 GHz (14.4–18.0 GHz) with a thickness of only 1.8 mm. The effective absorption (below −10 dB, 90% microwave absorption) bandwidth can be tuned between 6.2 GHz and 18.0 GHz for the absorber with a thin thickness in the range 1.5–4.0 mm. The results indicate that the microwave absorption properties of flower-like CuS hollow microspheres possess the advantages of broad bandwidth, strong absorption, lightweight and thin thickness are superior to those of other absorbing materials.

Journal ArticleDOI
TL;DR: In this paper, a P-doped g-C3N4 has been successfully synthesized using hexachlorocyclotriphosphazene, a low cost and environmentally benign compound, as phosphorus source, and guanidiniumhydrochloride as precursor, via a thermally induced copolymerization route.
Abstract: P-doped g-C3N4 has been successfully synthesized using hexachlorocyclotriphosphazene, a low cost and environmentally benign compound, as phosphorus source, and guanidiniumhydrochloride as g-C3N4 precursor, via a thermally induced copolymerization route. The obtained P-doped g-C3N4 showed excellent photocatalytic performance both in the photoreduction of H2O to produce H2 and the photodegradation of Rhodamine B (RhB). H2 evolution rate on modified g-C3N4 reached 50.6 μmol h−1, which is 2.9 times higher than that of the pure g-C3N4. RhB (10 mg L−1) was completely photodegraded within 10 min. The structure and texture properties of the P-doped g-C3N4 have been investigated in detail by XRD, FTIR, TEM, EDS and STEM. With the results of XPS and 31P NMR, a possible existing form of P atom in the framework g-C3N4 has been put forward. The introduction of a P atom significantly changes the electronic property of g-C3N4 and suppresses the recombination of photogenerated charge carriers, thus improving its photocatalytic performance.

Journal ArticleDOI
TL;DR: In this article, a series of highly efficient graphitic carbon nitride (CN) and NiFe-layered double hydroxide (LDH) composites were designed for visible light-induced photocatalytic H2 and O2 evolution.
Abstract: Exploiting the advantage of a layered architecture, layered graphitic carbon nitride (CN) and NiFe-layered double hydroxide (LDH) have been coupled in the present investigation to design a series of highly efficient novel CNLDH composites for visible light-induced photocatalytic H2 and O2 evolution. The syntheses of these composites were carried out using a facile weight impregnation method while varying the wt% of CN on LDH. The structural, optical, and morphological properties of these composites were characterized by various physicochemical techniques. The results indicate a tuned-in band gap energy within the range of pure LDH to pure CN. In addition, the remarkable quenching of the PL signal and prolonged photogenerated charge lifetime confirmed by TRPL spectra demonstrates the excellent photocatalytic activity of these composites. The activity could be ascribed to the dispersion of exfoliated CN over the brucite layer of LDH, in which strong energy transfer takes place in terms of charge carriers. The visible light-induced photocatalytic H2 and O2 evolution study resulted in an enhancement in the activity of the CNLDH10 composite with a H2 evolution rate of 1488 μmol 2 h−1 and O2 evolution rate of 886 μmol 2 h−1. The high photocatalytic activities of these composites may be due to good dispersion of exfoliated CN over the brucite layer of edge-shared MO6 octahedra, higher life time of charge carriers, low PL intensity, appropriate band gap energy and enhancement in photocurrent density.

Journal ArticleDOI
TL;DR: Results indicate that incorporation of GO into a PA membrane can effectively enhance its hydrophilicity and consequently improve its flux and antifouling properties and provides an effective way to develop high performance NF membranes with greater stability.
Abstract: Organic–inorganic hybrid materials are considered the most promising candidates in the preparation of nanofiltration (NF) membranes. The incorporation of nano-particles in a polymer matrix has provided a new approach for the preparation of membranes with enhanced permeability, high selectivity and improved anti-fouling properties. In this study, polyamide (PA) nanofiltration (NF) membranes embedded with various graphene oxide (GO) contents to improve the membrane flux and anti-fouling properties are proposed and successfully prepared for desalination applications. The prepared PA/GO membranes exhibited much higher flux than did pristine PA membranes. A twelve-fold increase in water flux, with a negligible change in salt rejection, was observed after incorporating GO (0.2 wt%) in the PA membrane. Addition of GO also provided a significant improvement in the anti-fouling property of the membrane due to an increase in the hydrophilicity of the membrane. These results indicate that incorporation of GO into a PA membrane can effectively enhance its hydrophilicity and consequently improve its flux and antifouling properties. Because no deleterious effect on the performance of the PA membrane was observed from this modification, this concept provides an effective way to develop high performance NF membranes with greater stability.

Journal ArticleDOI
TL;DR: InspInspired by the surface geometry and composition of the lotus leaf with its self-cleaning behavior, a robust superhydrophobic TiO2@fabric was further constructed by fluoroalkylsilane modification as a versatile platform for UV shielding, selfcleaning and oil-water separation as discussed by the authors.
Abstract: Inspired by the surface geometry and composition of the lotus leaf with its self-cleaning behavior, in this work, a TiO2@fabric composite was prepared via a facile strategy for preparing marigold flower-like hierarchical TiO2 particles through a one-pot hydrothermal reaction on a cotton fabric surface. In addition, a robust superhydrophobic TiO2@fabric was further constructed by fluoroalkylsilane modification as a versatile platform for UV shielding, self-cleaning and oil–water separation. The results showed TiO2 particles were uniformly distributed on the fibre surface with a high coating density. In comparison with hydrophobic cotton fabric, the TiO2@fabric exhibited a high superhydrophobic activity with a contact angle of ∼160° and a sliding angle lower than 10°. The robust superhydrophobic fabric had high stability against repeated abrasion without an apparent reduction in contact angle. The as-prepared composite TiO2@fabric demonstrated good anti-UV ability. Moreover, the composite fabric demonstrated highly efficient oil–water separation due to its extreme wettability contrast (superhydrophobicity/superoleophilicity). We expect that this facile process can be readily and widely adopted for the design of multifunctional fabrics for excellent anti-UV, effective self-cleaning, efficient oil–water separation, and microfluidic management applications.

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TL;DR: Li4Ti5O12 has been considered as one of the most promising anode candidates for the next-generation large-scale power lithium-ion batteries used for HEVs or EVs because it has a high potential of around 1.55 V during charge and discharge.
Abstract: Lithium-ion batteries are considered as one of the most promising power sources for energy storage system for a wide variety of applications such as electric vehicles (EVs) or hybrid electric vehicles (HEVs). The anode material often plays an important role in the determination of the safety and cycling life of lithium-ion batteries. Among all anode materials, spinel Li4Ti5O12 has been considered as one the most promising anode candidates for the next-generation large-scale power lithium-ion batteries used for HEVs or EVs because it has a high potential of around 1.55 V (vs. Li/Li+) during charge and discharge, excellent cycle life due to the negligible volume change, and high thermal stability and safety. In this review, we present an overview of the breakthroughs in the past decade in the synthesis and modification of both the chemistry and morphology of Li4Ti5O12. An insight into the future research and further development of Li4Ti5O12 composites is also discussed.