Showing papers in "Journal of Materials Chemistry in 2016"

Polymer electrolytes for lithium polymer batteries

Abstract: In this review, state-of-the-art polymer electrolytes are discussed with respect to their electrochemical and physical properties for their application in lithium polymer batteries. We divide polymer electrolytes into the two large categories of solid polymer electrolytes and gel polymer electrolytes (GPE). The performance requirements and ion transfer mechanisms of polymer electrolytes are presented at first. Then, solid polymer electrolyte systems, including dry solid polymer electrolytes, polymer-in-salt systems (rubbery electrolytes), and single-ion conducting polymer electrolytes, are described systematically. Solid polymer electrolytes still suffer from poor ionic conductivity, which is lower than 10−5 S cm−1. In order to further improve the ionic conductivity, numerous new types of lithium salt have been studied and inorganic fillers have been incorporated into solid polymer electrolytes. In the section on gel polymer electrolytes, the types of plasticizer and preparation methods of GPEs are summarized. Although the ionic conductivity of GPEs can reach 10−3 S cm−1, their low mechanical strength and poor interfacial properties are obstacles to their practical application. Significant attention is paid to the incorporation of inorganic fillers into GPEs to improve their mechanical strength as well as their transport properties and electrochemical properties.

A review on noble-metal-free bifunctional heterogeneous catalysts for overall electrochemical water splitting

Abstract: Production of hydrogen by water splitting is an appealing solution for sustainable energy storage. Development of bifunctional catalysts that are active for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is a key factor in enhancing electrochemical water splitting activity and simplifying the overall system design. Here, recent developments in HER–OER bifunctional catalysts are reviewed. Several main types of bifunctional water splitting catalysts such as cobalt-, nickel- and iron-based materials are discussed in detail. Particular attention is paid to their synthesis, bifunctional catalytic activity and stability, and strategies for activity enhancement. The current challenges faced are also concluded and future perspectives towards bifunctional water splitting electrocatalysts are proposed.

Review on recent advances in nitrogen-doped carbons: preparations and applications in supercapacitors

Abstract: It is of great interest to develop new carbon-based materials as electrodes for supercapacitors because the conventional electrodes of activated carbons in supercapacitors cannot meet the ever-increasing demands for high energy and power densities for electronic devices. Due to their high electronic conductivity and improved hydrophilic properties, together with their easy syntheses and functionalization, N-doped carbons have shown a great potential in energy storage and conversion applications. In this review, after a brief introduction of electrochemical capacitors, we summarize the advances, in the recent six years, in the preparation methods of N-doped carbons for applications in supercapacitors. We also discuss and predict futuristic research trends towards the design and syntheses of N-doped carbons with unique properties for electrochemical energy storage.

A review of one-dimensional TiO2 nanostructured materials for environmental and energy applications

Abstract: One-dimensional TiO2 (1D TiO2) nanomaterials with unique structural and functional properties have been extensively used in various fields including photocatalytic degradation of pollutants, photocatalytic CO2 reduction into energy fuels, water splitting, solar cells, supercapacitors and lithium-ion batteries. In the past few decades, 1D TiO2 nanostructured materials with a well-controlled size and morphology have been designed and synthesized. Compared to 0D and 2D nanostructures, more attention has been paid to 1D TiO2 nanostructures due to their high aspect ratio, large specific surface area, and excellent electronic or ionic charge transport properties. In this review, we present the crystal structure of TiO2 and the latest development on the fabrication of 1D TiO2 nanostructured materials. Besides, we will look into some critical engineering strategies that give rise to the excellent properties of 1D TiO2 nanostructures such as improved enlargement of the surface area, light absorption and efficient separation of electrons/holes that benefit their potential applications. Moreover, their corresponding environmental and energy applications are described and discussed. With the fast development of the current economy and technology, more and more effort will be put into endowing TiO2-based materials with advanced functionalities and other promising applications.

Nanostructured catalysts for electrochemical water splitting: current state and prospects

Abstract: Hydrogen is an ideal candidate for the replacement of fossil fuels in the future due to zero emission of carbonaceous species during its utilization. Water electrolysis is a dependable link of primary renewable energy and stable hydrogen energy. In this work, the fundamentals of water electrolysis, current popular electrocatalysts developed for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in liquid electrolyte water electrolysis are reviewed. The main HER catalysts include noble metals, non-noble metals and composites, noble metal-free alloys, metal carbides, chalcogenides, phosphides and metal-free materials while the OER catalysts are focused on efficient Co-based, Ni-based materials and layered double hydroxide (LDH) materials. The strategies to improve catalytic activity, long-term durability and endurance to electrochemical erosion are introduced. The main challenges and future prospects for the further development of electrodes for water electrolysis are discussed. It is expected to give guidance for the development of novel low-cost nanostructured electrocatalysts for electrochemical water splitting.

First principles study on electrochemical and chemical stability of solid electrolyte–electrode interfaces in all-solid-state Li-ion batteries

Abstract: All-solid-state Li-ion batteries based on ceramic solid electrolyte materials are a promising next-generation energy storage technology with high energy density and enhanced cycle life. The poor interfacial conductance is one of the key limitations in enabling all-solid-state Li-ion batteries. However, the origin of this poor conductance has not been understood, and there is limited knowledge about the solid electrolyte–electrode interfaces in all-solid-state Li-ion batteries. In this study, we performed first principles calculations to evaluate the thermodynamics of the interfaces between solid electrolyte and electrode materials and to identify the chemical and electrochemical stabilities of these interfaces. Our computation results reveal that many solid electrolyte–electrode interfaces have limited chemical and electrochemical stability, and that the formation of interphase layers is thermodynamically favorable at these interfaces. These formed interphase layers with different properties significantly affect the electrochemical performance of all-solid-state Li-ion batteries. The mechanisms of applying interfacial coating layers to stabilize the interface and to reduce interfacial resistance are illustrated by our computation. This study demonstrates a computational scheme to evaluate the chemical and electrochemical stability of heterogeneous solid interfaces. The enhanced understanding of the interfacial phenomena provides the strategies of interface engineering to improve performances of all-solid-state Li-ion batteries.

MXene: a promising photocatalyst for water splitting

Abstract: Identifying suitable photocatalysts for photocatalytic water splitting to produce hydrogen fuel via sunlight is an arduous task by the traditional trial-and-error method. Thanks to the progress of density functional theory, one can nowadays accelerate the process of finding candidate photocatalysts. In this work, by ab initio calculations, we investigated 48 two-dimensional (2D) transition metal carbides also referred to as MXenes to understand their photocatalytic properties. Our results highlight 2D Zr2CO2 and Hf2CO2 as the candidate single photocatalysts for possible high efficiency photocatalytic water splitting. A significant property of 2D Zr2CO2 and Hf2CO2 is that they exhibit unexpectedly high and directionally anisotropic carrier mobility, which may effectively facilitate the migration and separation of photogenerated electron–hole pairs. Meanwhile, these two MXenes also exhibit very good optical absorption performance in the wavelength ranging approximately from 300 to 500 nm. The stability of 2D Zr2CO2 and Hf2CO2 in liquid water is expected to be good based on ab initio molecular dynamics simulations. Finally, the adsorption and decomposition of water molecules on the 2D Zr2CO2 surface and the subsequent formation process of hydrogen were studied, which contributes to the unravelling of the micro-mechanism of photocatalytic hydrogen production on MXenes. Our findings will open a new way to facilitate the discovery and application of MXenes for photocatalytic water splitting.

Flexible electrodes and supercapacitors for wearable energy storage: a review by category

Abstract: Supercapacitors are important energy storage devices capable of delivering energy at a very fast rate. With the increasing interest in portable and wearable electronic equipment, various flexible supercapacitors (FSCs) and flexible electrodes (FEs) have been investigated widely and constantly in recent years. Currently-developed FEs/FSCs exhibit myriad physical forms and functional features and form a complicated and extensive system. Herein, we summarize the recent results about FEs/FSCs and present this review by categories. According to different micro-structures and macroscopic patterns, the existing FEs/FSCs can be divided into three types: fiber-like FEs/FSCs; paper-like FEs/FSCs; and three-dimensional porous FEs (and corresponding FSCs). Subsequently each type of the FEs/FSCs is further sub-classified based on their construction rules, and mechanical and electrochemical properties. To our best knowledge, this is the first time such a hierarchical and detailed classification strategy has been propose. We believe it will be beneficial for researchers around the world to understand FEs/FSCs. In addition, we bring up some fresh ideas for the future development of wearable energy storage devices.

Transition metals (Fe, Co, and Ni) encapsulated in nitrogen-doped carbon nanotubes as bi-functional catalysts for oxygen electrode reactions

Abstract: The development of efficient and cheap bifunctional oxygen electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to be applied in rechargeable metal–air batteries and unitized generative fuel cells (URFCs) operated with alkaline electrolytes is highly crucial and challenging. Here we report high-performance bifunctional electrocatalysts of transition metal nanoparticles encapsulated in nitrogen-doped carbon nanotubes (M/N-CNTs, M = Fe, Co, and Ni). The optimized Co/N-CNT hybrid shows the highest efficient bifunctional catalytic activity and excellent stability towards both the ORR and OER. The oxygen electrode activity parameter ΔE (the criteria for judging the overall catalytic activity of bifunctional electrocatalysts) value for Co/N-CNTs is 0.78 V, which surpasses those of Pt/C and RuO2 catalysts and most of the non-precious metal based bifunctional electrocatalysts reported in the previous literature studies. Furthermore, excellent long-term catalytic durability holds great promise in fields of renewable energy applications.

A review on the recent progress, challenges and perspective of layered double hydroxides as promising photocatalysts

Abstract: Considering the previous work on layered double hydroxides (LDHs) as novel photocatalysts, research on this group of materials has become one of the most exciting subjects of today. LDH has become an important class of layered materials having prospects in photocatalysis, wherein great attention has been paid to the exhaustive aerobic degradation of pollutants, photocatalytic water splitting, and CO2 photo-reduction. The unique structure, uniform distribution of different metal cations in the brucite layer, surface hydroxyl groups, flexible tunability, intercalated anions with interlayer spaces, swelling properties, oxo-bridged linkage, and high chemical stability are some of the important advantages of this group of materials. This article provides an up-to-date review on significant progress in the fabrication of LDH photocatalytic systems aiming at environmental clean-up and energy production, such as degradation of pollutants, photocatalytic H2 generation and photocatalytic CO2-reduction. This article, after discussing the recent significant progress in the synthesis of different photoactive LDH materials and photocatalytic applications through their structural and electronic properties, considers many typical examples. In particular, recent progress on the emerging strategies of LDH to improve their photocatalytic activity is also presented. Eventually, the future challenges and outlooks for this group of materials are also discussed.

Benchmarking nanoparticulate metal oxide electrocatalysts for the alkaline water oxidation reaction

Abstract: Nanoparticulate metal-oxide catalysts are among the most prevalent systems for alkaline water oxidation. However, comparisons of the electrochemical performance of these materials have been challenging due to the different methods of attachment, catalyst loadings, and electrochemical test conditions reported in the literature. Herein, we have leveraged a conventional drop-casting method that allows for the successful adhesion of a wide range of nanoparticulate catalysts to glassy-carbon electrode surfaces. We have applied this adhesion method to prepare catalyst films from 16 crystalline metal-oxide nanoparticles with a constant loading of 0.8 mg cm−2, and evaluated the resulting nanoparticulate films for the oxygen evolution reaction under conditions relevant to an integrated solar fuels device. In general, the activities of the adhered nanoparticulate films are similar to those of thin-film catalysts prepared by electrodeposition or sputtering, achieving 10 mA cm−2 current densities per geometric area at overpotentials of ∼0.35–0.5 V.

Recent progress in electron transport layers for efficient perovskite solar cells

Abstract: Thin-film photovoltaics based on organic–inorganic hybrid perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. Over the past several years, we have witnessed a great and unexpected progress in organic–inorganic perovskite solar cells (PSCs). The power conversion efficiency (PCE) increased from 3.8% to 20.1% and exceeded the highest efficiency of conventional dye-sensitized solar cells. Here, the focus is specifically on the recent developments of the electron transport layer (ETL) in PSCs, which is an important part for high performing PSCs. This review briefly discusses the development of the structure of PSCs, and we attempt to give a systematic introduction about the optimization of ETL and its related interfaces for efficient PSCs. Moreover, the introduction of appropriate interfacial materials is another important issue to improve PSC performance by optimizing the interfacial electronic properties between the perovskite layer and the charge-collecting electrode. Besides, some related issues such as device stability and hysteresis behavior are also discussed here.

Room temperature lithium superionic conductivity in high entropy oxides

Abstract: Impedance spectroscopy measurements evidence superionic Li+ mobility (>10−3 S cm−1) at room temperature and fast ionic mobility for Na+ (5 × 10−6 S cm−1) in high entropy oxides, a new family of oxide-based materials with the general formula (MgCoNiCuZn)1−x−yGayAxO (with A = Li, Na, K). Structural investigations indicate that the conduction path probably involves oxygen vacancies.

Robust fluorine-free superhydrophobic PDMS–ormosil@fabrics for highly effective self-cleaning and efficient oil–water separation

Abstract: Superhydrophobic cotton fabrics were prepared via a facile and environmentally friendly strategy to deposit an organically modified silica aerogel (ormosil) thin film onto the fabrics first, followed by polydimethylsiloxane (PDMS) topcoating. The PDMS–ormosil coating displayed a uniform 3D fractal-like structure with numerous loose micro-scale pores, while the PDMS layer increased the binding strength of the hierarchical ormosil film to form a highly robust porous network on the fibers. In comparison with hydrophilic cotton fabrics, the modified cotton fabric exhibited a highly superhydrophobic activity with a water contact angle higher than 160° and a sliding angle lower than 10°. The as-constructed PDMS–ormosil@fabrics are able to withstand 100 cycles of abrasion and 5 cycles of accelerated machine wash without an apparent decrease of superhydrophobicity. In addition, the superhydrophobic cotton fabrics are very stable in strongly acidic and alkaline solutions. Furthermore, the superhydrophobic coating has no or negligible adverse effect on the important textile physical properties of the cotton fabric, such as the strength, air permeability, and flexibility. The composite super-antiwetting fabrics have demonstrated excellent anti-fouling, self-cleaning ability and are highly efficient in oil–water separation for various oil–water mixtures. This facile synthesis technique has the advantages of scalable fabrication of multifunctional fabrics for potential applications in self-cleaning and versatile water–oil separation.

Recent progress and perspectives on bi-functional oxygen electrocatalysts for advanced rechargeable metal–air batteries

Abstract: With continued dependence on carbon-based fuels and rising concerns of environmental issues, the development of rechargeable metal–air batteries has recently gained tremendous attention. However, due to the slow kinetics of electrochemical oxygen reactions, the charge and discharge processes of a rechargeable metal–air battery must be catalyzed by using bi-functional catalysts that are active towards both the oxygen reduction and oxygen evolution reactions. This review focuses on recent developments in bi-functional catalysts and their catalytic activity in relation to materials composition, morphology, and crystal structure obtained through various synthetic techniques. The discussion is divided into sections based on the main types of recent bi-functional catalysts such as transition metal- and carbon-based materials, and hybrids which consist of the two. The subsections are then divided based on the metal substituents, types of dopant, degree of doping, and defect densities, discussing the effects of composition. In parallel, morphological effects on the catalytic activity, such as unique nanostructured design, surface area enhancements, and porosity, are also discussed. Currently, bi-functional oxygen electrocatalyst research is heading in the direction of reducing the loading of precious metals, and developing cost-competitive non-precious metal- and carbon-based catalysts to enable commercialization of rechargeable metal–air batteries for various applications including electric-drive vehicles and smart-grid energy storage. To understand the origin of bi-functional catalytic activity, future catalyst research should be conducted in combination with in situ characterizations, and computational studies, which will allow exploitation of active sites to maximize the efficacy of bi-functional catalysts.

Significantly enhanced recoverable energy storage density in potassium–sodium niobate-based lead free ceramics

Abstract: Ceramic-based dielectric materials are regarded as the best candidates for advanced pulsed power capacitors because of their excellent mechanical and thermal properties. Nevertheless, lead-free bulk ceramics show relatively low recoverable energy storage density (Wrec < 2 J cm−3) owing to their low dielectric breakdown strength (DBS < 200 kV cm−1). In order to significantly increase Wrec, we proposed a strategy (compositions drive the grain size to submicrometer) to improve the DBS of lead-free ceramics. In this work, (1 − x)(K0.5Na0.5)NbO3–xSrTiO3 (KNN–ST) ceramics were chosen as a representative to verify the validity of this strategy. The (1 − x)KNN–xST ceramics (x = 0.15 and 0.20) with submicrometer grains (about 0.3 μm) were prepared using pressureless solid state sintering. A large Wrec (4.03 J cm−3) and DBS (400 kV cm−1 with a thickness of 0.2 mm) were achieved for 0.85KNN–0.15ST ceramics. The value of 4.03 J cm−3 is superior to all other Wrec in lead-free bulk ceramics and 2–3 times larger than that of other lead-free bulk ceramics. A large Wrec (3.67 J cm−3) and energy storage efficiency (72.1%) were simultaneously achieved for 0.80KNN–0.20ST ceramics. The results confirm that the (1 − x)KNN–xST ceramics (x = 0.15 and 0.20) are desirable materials for advanced pulsed power capacitors. The findings in this study could push the development of a series of KNN-based ceramics with enhanced DBS and Wrec in the future. On the other hand, this work could broaden the applications of KNN materials in a new field.

Metal–organic framework nanosheets for fast-response and highly sensitive luminescent sensing of Fe3+

Abstract: The first luminescent two-dimensional MOF nanosheets NTU-9-NS Ti2(HDOBDC)2(H2DOBDC) (H2DOBDC = 2,5-dihydroxyterephthalic acid) fabricated via top-down delamination have been realized for the highly sensitive sensing of Fe3+ with a fast response. The highly dispersive nature and highly accessible active sites on the surface of the 2D NTU-9-NS nanosheets enable them to have close contact with targeted metal ions, which leads to the highly sensitive sensing of Fe3+ ions, with a fast response time within seconds and the best detection limit performance of 0.45 μM among MOF materials. The fast response and highly sensitive Fe3+ sensing based on the NTU-9-NS nanosheets sensor material highlights the promise of the two-dimensional MOF nanosheet approach for luminescent sensing applications. This work contributes to the development of research on two-dimensional MOF nanosheets materials with targeted and specific recognition for the application of biological and environmental luminescent sensors.

Facile synthesis of an accordion-like Ni-MOF superstructure for high-performance flexible supercapacitors

Abstract: Metal–organic frameworks have received increasing attention as promising electrode materials in supercapacitors. In this study, we have successfully synthesized a novel accordion-like Ni-MOF superstructure ([Ni3(OH)2(C8H4O4)2(H2O)4]·2H2O), for the first time, and used it as an electrode material for supercapacitors. The supercapacitors with the novel electrode exhibited excellent electrochemical performance. For example, the accordion-like Ni-MOF electrode showed specific capacitances of 988 and 823 F g−1 at current densities of 1.4 and 7.0 A g−1, respectively, while maintaining outstanding cycling stability (capacitance retention of 96.5% after 5000 cycles at a current density of 1.4 A g−1). More importantly, the accordion-like Ni-MOF and activated carbons were assembled into a high-performance flexible solid-state asymmetric supercapacitor with a specific capacitance of 230 mF cm−2 at a current density of 1.0 mA cm−2. The cycle test showed that the device can offer 92.8% capacity of the initial capacitance at 5.0 mA cm−2 after 5000 cycles with little decay. The maximum energy density of the device can achieve 4.18 mW h cm−3 and the maximum power density can also achieve 231.2 mW cm−3.

Hierarchical porous carbon microtubes derived from willow catkins for supercapacitor applications

Abstract: With willow catkins as highly accessible carbon sources, hierarchical porous carbon microtubes (denoted as HPNCTs) have been successfully prepared by a facile carbonization and subsequent KOH activation process. The resulting materials not only inherited the natural tubular morphology of willow catkins, but also developed a hierarchical porous structure by activation, with nitrogen from the biomass being self-doped in the resulting carbon. A maximum specific surface area of 1775.7 m2 g−1 with a pore volume of 0.8516 cm3 g−1 was achieved for HPNCT-800. When evaluated as an electrode by a three-electrode system in 6 M KOH aqueous solution, the material exhibited a high gravimetric capacitance of 292 F g−1 at a current density of 1 A g−1, with a good rate capability of 83.5% retention at 10 A g−1. HPNCT-800 was further employed in a coin-type symmetric device with 1 M LiPF6 electrolyte, and exhibited a high energy density of 37.9 W h kg−1 at a power density of 700 W kg−1, with excellent cycling stability with 90.6% retention after 4000 cycles. By taking advantage of the unique structure of abundant biomass from nature, this work sheds light on the creation of advanced porous carbon materials towards energy storage applications.

Recent advances in dye-sensitized semiconductor systems for photocatalytic hydrogen production

Abstract: Photocatalytic water splitting by solar light has received tremendous attention for the production of clean and renewable hydrogen energy from water. Some challenges still remain in improving the solar-to-hydrogen energy conversion efficiency, such as utilizing longer-wavelength photons and enhancing the photocatalytic activity and stability of H2 production over semiconducting materials. Dye sensitization, as a successful strategy for extending the spectral responsive region (even to near-IR light) of wide bandgap semiconductors for H2 production, was developed more than 30 years ago, but it still lacks the corresponding specialized review. This review emphasizes especially the fundamental aspects and the research advances in heterogeneous dye-sensitized semiconductor suspension systems for visible (and even near-IR) light responsive photocatalytic H2 production, and the commonly used dyes, semiconductors, co-catalysts and electron donors are systematically discussed. Also, a short perspective on the challenges and new directions in this field is proposed, which would be of great interest in the field of solar fuel conversion.

Doping graphene with boron: a review of synthesis methods, physicochemical characterization, and emerging applications

Abstract: Graphene based materials can be effectively modified by doping in order to specifically tailor their properties toward specific applications. So far the most used and widely investigated dopant heteroatom is probably nitrogen. However, boron is also an equally important element that can induce novel and complementary properties leading to specific implementation in alternative devices and technologies. In this paper, we survey the most recent preparation methods of boron doped graphene, including materials with specific morphology such as nanoribbons, quantum dots and 3D interconnected systems. We illustrate the results of theoretical and experimental studies dealing with the description and understanding of the main structural, electronic and chemical properties of this material. The emerging applications of boron doped graphene in several technological fields such as electrochemistry, sensors, photovoltaics, catalysis and biology are extensively reviewed.

Improving the functionality of carbon nanodots: doping and surface functionalization

Abstract: Distinct from conventional carbon nanostructures, such as fullerene, graphene, and carbon nanotubes, carbon nanodots (C-dots) exhibit unique properties such as strong fluorescence, high photostability, chemical inertness, low toxicity, and biocompatibility. Various synthesis routes for C-dots have been developed in the last few years, and now intense research efforts have been focused on improving their functionality. In this aspect, doping and surface functionalization are two major ways to control the chemical, optical, and electrical properties of C-dots. Doping introduces atomic impurities into C-dots to modulate their electronic structure, and surface functionalization modifies the C-dot surface with functional molecules or polymers. In this review, we summarize recent progress in doping and surface functionalization of C-dots for improving their functionality, and offer insight into controlling the properties of C-dots for a variety of applications ranging from biomedicine to optoelectronics to energy.

MXene as a novel intercalation-type pseudocapacitive cathode and anode for capacitive deionization

Abstract: In this proof-of-concept study, we introduce and demonstrate MXene as a novel type of intercalation electrode for desalination via capacitive deionization (CDI). Traditional CDI cells employ nanoporous carbon electrodes with significant pore volume to achieve a large desalination capacity via ion electrosorption. By contrast, MXene stores charge by ion intercalation between the sheets of its two-dimensional nanolamellar structure. By this virtue, it behaves as an ideal pseudocapacitor, that is, showing capacitive electric response while intercalating both anions and cations. We synthesized Ti3C2-MXene by the conventional process of etching ternary titanium aluminum carbide i.e., the MAX phase (Ti3AlC2) with hydrofluoric acid. The MXene material was cast directly onto the porous separator of the CDI cell without added binder, and exhibited very stable performance over 30 CDI cycles with an average salt adsorption capacity of 13 ± 2 mg g−1.

Electrospun nanofibers as a platform for advanced secondary batteries: a comprehensive review

Abstract: Poor electrochemical performances of materials in commercial lithium-ion batteries (LIBs) make it difficult to realize battery technologies for future electric power applications such as energy storage systems and electric vehicles. To reach beyond the horizon of state-of-the-art LIBs, the exploration of next generation batteries composed of rationally designed nanomaterials in consideration of the structure, phase and element influencing the battery performance is critical. By virtue of the simple set-up, versatility, size controllability and mass-productivity of electrospinning, one-dimensional (1D) nanofibers (NFs) produced via electrospinning are attractive candidates for the construction of advanced secondary batteries. A comprehensive review of the forefront in the development of electrospun NFs as advanced materials of next generation LIBs, sodium-ion batteries (NIBs), lithium–sulfur batteries and lithium–air batteries with particular emphasis on synthesis and improved energy and power density, and cyclability is presented. In this review, we highlight the recent advancements in electrospun 1D nano-architectures with large surface area to volume ratios and controllable morphologies as anodes, cathodes, separators, electrolytes and even catalytic materials. Furthermore, current challenges and prospects of electrospun NFs in both academia and industry are also discussed. We expect that this review opens up new research activities in a variety of research fields including advanced rechargeable batteries.

Thermal exfoliation of hexagonal boron nitride for effective enhancements on thermal stability, flame retardancy and smoke suppression of epoxy resin nanocomposites via sol–gel process

Abstract: The structure of hexagonal boron nitride (h-BN) is similar to that of graphite before functionalization and exfoliation. For applications in polymer nanocomposites, chemical exfoliation is a more economically attractive route to few-layer h-BN nanosheets. A thermal oxidation process of h-BN powder could achieve large scale exfoliation and hydroxylated functionalization, as described in prior literature. In this report, hydroxylated h-BN (BNO) was prepared by heating h-BN under air, and then covalently incorporated into epoxy resin modified with (3-isocyanatopropyl)triethoxysilane to prepare epoxy resin (EP) nanocomposites by sol–gel process. The structure and morphology of BNO were well characterized. BNO was dispersed in the EP matrix with the form of mainly exfoliated and intercalated structures, and formed strong interfacial interaction with the matrix. Thermogravimetric analysis results revealed that BNO significantly improved thermal stability and thermal oxidative resistance of EP nanocomposites at high temperature. The char yield and the temperature at 50 wt% mass loss were increased and the maximum mass loss rate was remarkably reduced. Moreover, the addition of 3 wt% BNO led to extremely high Tg of EP nanocomposite, 42.7 °C higher than that of pure EP, due to improved crosslinking density and confinement effect of BNO sheets on the mobility of polymer networks. Cone calorimeter test results indicated that fire safety properties of EP nanocomposites were also enhanced by the addition of BNO, such as 53.1% reduction in peak heat release rate and 32.6% decrease in total heat release, and decreased release of smoke and toxic gases. The mechanism for enhanced fire retardancy is that thermally stable condensed barrier consisting of h-BN sheets and silicon dioxide for heat and mass transfer protects the matrix from further combustion.

Review: carbon onions for electrochemical energy storage

Abstract: Carbon onions are a relatively new member of the carbon nanomaterials family. They consist of multiple concentric fullerene-like carbon shells which are highly defective and disordered. Due to their small size of typically below 10 nm, the large external surface area, and high conductivity they are used for supercapacitor applications. As electrode materials, carbon onions provide fast charge/discharge rates resulting in high specific power but present comparatively low specific energy. They improve the performance of activated carbon electrodes as conductive additives and show suitable properties as substrates for redox-active materials. This review provides a critical discussion of the electrochemical properties of different types of carbon onions as electrode materials. It also compares the general advantages and disadvantages of different carbon onion synthesis methods. The physical and chemical properties of carbon onions, in particular nanodiamond-derived carbon onions, are described with emphasis on those parameters especially important for electrochemical energy storage systems, including the structure, conductivity, and porosity. Although the primary focus of current research is on electrode materials for supercapacitors, the use of carbon onions as conductive additives and for redox-active species is also discussed.

Surface zwitterionic functionalized graphene oxide for a novel loose nanofiltration membrane

Abstract: Surface zwitterionization of graphene oxide (GO) was firstly conducted by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface via reverse atom transfer radical polymerization (RATRP). Then, a novel type of GO-PSBMA/polyethersulfone (PES) loose nanofiltration membrane (NFM) was constructed by mixing with modified GO composites via phase inversion. FTIR, XRD, TEM, XPS and TGA were applied to analyze the chemical composition and morphology, confirming a favorable synthesis of GO-PSBMA composites. Besides, the effect of the embedded GO-PSBMA nanoplates on the morphology and overall performance of the hybrid membranes was systematically investigated based on the SEM images, water contact angle, zeta potential, and fouling parameters. It was found that the water flux of the hybrid membrane was greatly enhanced from 6.44 L m−2 h−1 bar−1 to 11.98 L m−2 h−1 bar−1 when the GO-PSBMA content increased from 0 to 0.22 wt%. The antifouling tests revealed that the GO-PSBMA embedded membranes had an excellent antifouling performance: a high flux recovery ratio (ca. 94.4%) and a low total flux decline ratio (ca. 0.18). Additionally, the hybrid membranes exhibited a distinct advance in the mechanical strength due to the addition of highly rigid GO. Notably, compared with unmodified membranes, the hybrid membranes had a higher retention of Reactive Black 5 (99.2%) and Reactive Red 49 (97.2%), and a lower rejection of bivalent salts (10% for Na2SO4) at an operational pressure of 0.4 MPa, rendering the membranes promising for dye/salt fractionation.

Robust superhydrophobic attapulgite coated polyurethane sponge for efficient immiscible oil/water mixture and emulsion separation

Abstract: Separation of oil/water mixtures has become an increasingly important subject worldwide because of frequent oil spill incidents and industrial oily wastewater. The filter materials for the mixtures separation need to collect first and then filter, which is energy-intensive and cumbersome. Utilization of adsorbents appears to be an economical and direct way for mixture disposal. In this study, the superhydrophobic polyurethane (PU) sponge is fabricated by coating superhydrophobic attapulgite (APT) onto its skeleton surface. The coated PU sponges exhibit robust superhydrophobicity and high adsorption capability under a series of harsh conditions, which are used for the separation of mixtures of oil and various corrosive solutions and hot water. Moreover, the coated PU sponges can selectively adsorb oils from mixtures under extreme and harsh turbulent conditions. Furthermore, the coated PU sponge connected to a vacuum system could remove up to 3200 times its self-weight in kerosene within 20 s under a vacuum degree of about 30 kPa. More importantly, the coated PU sponges can separate tiny oil droplets from surfactant-stabilized oil-in-water emulsions with a separation efficiency of over 99.87% by employing a compression and agitation procedure. All of these characteristics make the coated PU sponge a promising adsorbent for realizing oil and organic pollutant removal in realistic aquatic environments.

A superior low-cost amorphous carbon anode made from pitch and lignin for sodium-ion batteries

Abstract: Sodium-ion batteries (SIBs) are a promising candidate for grid electricity storage due to their potential low cost. The development of anode materials is a crucial step to promote the commercialization of SIBs, and amorphous carbon materials are likely to be the most promising alternatives among all proposed anode materials. However, the cost of the reported carbon materials is still very high due to the expensive precursors and their low carbon yield. Here, we report an amorphous carbon (AC) material made from low cost pitch. The amorphous carbon material with an amazing high carbon yield of 57% was achieved by utilizing the emulsification interaction between pitch and lignin to suppress the graphitization of pitch during the carbonization. The effects of heat-treatment temperatures and the pitch/lignin mass ratios on the morphology, microstructure and the electrochemical performance of AC were systematically investigated. By optimizing experimental conditions, we achieved one representative AC with a suitable morphology and microstructure, which exhibits promising performances with a high reversible capacity of 254 mA h g−1, a high initial coulombic efficiency of 82% and excellent cycling stability. This is the first demonstration that the pitch can be successfully applied in fabricating amorphous carbon anode materials for SIBs with superior low cost and high performance.

Carbon materials as oil sorbents: a review on the synthesis and performance

Abstract: Oil spill accidents have urged scientists across the world to develop an immediate cleanup technology because the spilled oil significantly affects the ecological and environmental system. Superhydrophobic and superoleophilic materials have shown potential application in the field of oil spill cleanup due to their outstanding absorption capabilities, high selectivity, chemical inertness and excellent recyclability. In this regard, carbon-based absorbents have been considered to be the best candidates as they possess high surface area, low density, excellent mechanical properties, good chemical stability, environmental friendliness and large pore volume. Carbon aerogels, graphene or carbon nanotubes (CNTs) coated sponges, carbon nanotube forests, graphene foams or sponges, carbon coatings, activated carbon, porous carbon nanoparticles and carbon fibers have been widely investigated for water filtration, water/oil separation, oil-spill cleanup, wastewater treatment, gas separation and purification. In this paper, the synthesis, applications and reusability of these carbon-based absorbents have been reviewed and their performances compared.