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Freestanding electrodes without the influences of additives have been considered as a kind of ideal electrode structure in the field of capacitive deionization (CDI). However, subjected to conductivity, available surface areas, hydrophilicity and etc., effectively construction of freestanding CDI electrodes with high water desalination performance still face great challenges. Herein, we will demonstrate a unique N-doped graphene freestanding porous membrane electrode with excellent water desalination performance. The preparation process mainly includes the assembly of core-shell composites with incomplete graphene oxide shells into bulk membranes using compression molding method and the heat-treatment under NH3 atmosphere. These reserved spherical shells with loopholes and N-doping make up the freestanding membrane electrodes with network porous architecture. The interconnected sphere shells efficiently improve the availability of surface and pores in the monolithic assembly, while the doping of nitrogen element further enhances the accessibility of graphene-based surface by the electrolyte. As a result, such graphene carbonaceous freestanding electrodes exhibit excellent water desalination performance with a high CDI capacity of about 21.8 mg/g in NaCl solution. Moreover, such freestanding membrane electrodes also possess good desalination abilities towards some other salts such as KCl, CaCl2 and MgCl2, suggesting their potential applications in complex brine solution.

High-performance electromagnetic interference (EMI) shielding material that that can function properly under extreme working conditions is critical for their practical applications. Herein, flexible and highly conductive meta-aramid (PMIA) nonwoven fabrics were fabricated by combining polydopamine (PDA) modification and electroless silver plating. The PDA modification greatly enhanced the efficient deposition of silver nanoparticles (AgNPs) and the interfacial cohesion between the AgNPs and the PMIA fibers. The silver-coated PMIA nonwoven fabric exhibited an electrical conductivity as high as 0.29 Ω/sq, an excellent EMI shielding effectiveness (SE) of 92.6 dB and a high absolute EMI SE of 8194.7 dB cm2 g−1. In addition, the silver-coated PMIA nonwoven fabric maintained high electrical conductivity and EMI SE after being subjected to washing, bending and torsion deformations, high/low temperature, strong acidic/alkaline solutions and different organic solvents. These results have clearly demonstrated that PMIA nonwoven fabric can be made highly electrically conductive by using a simple and highly scalable method. It holds great promise for the applications in EMI shielding materials that can be used in various harsh conditions.

Cartilage adheres to subchondral bone via a specific osteochondral interface tissue where forces are transferred from soft cartilage to hard bone without conferring fatigue damage over a lifetime of load cycles. However, the fine structure and mechanical properties of the osteochondral interface tissue remain unclear. Here, we identified an ultrathin ∼20-30 μm graded calcified region with two-layered micronano structures of osteochondral interface tissue in the human knee joint, which exhibited characteristic biomolecular compositions and complex nanocrystals assembly. Results from finite element simulations revealed that within this region, an exponential increase of modulus (3 orders of magnitude) was conducive to force transmission. Nanoscale heterogeneity in the hydroxyapatite, coupled with enrichment of elastic-responsive protein-titin, which is usually present in muscle, endowed the osteochondral tissue with excellent mechanical properties. Collectively, these results provide novel insights into the potential design for high-performance interface materials for osteochondral interface regeneration.

Kilohertz high frequency electrochemical capacitors (HF-ECs), with a compact size, are being actively investigated with the aim for line-frequency ripple current filtering and other applications. However, the reported performance, particularly achievable capacitance density, the frequency response, and the phase angle that are directly determined by the electrode structure is still far from satisfactory that hinders its practical application prospect. In this work, metal organic framework (Prussian Blue, PB) is introduced as a structural mediator to develop three-dimensional vertical graphene architecture, or edge-oriented graphene (EOG) on a current collector via a 5-min rapid plasma carbonization and deposition process. With several prominent merits integrated together in the resulted EOG electrode structure, HF-ECs exhibit very low equivalent series resistance (ESR) of 40 ​mΩ ​cm−2 and attractive cell capacitance of 1.02 ​mF ​cm−2 and phase angle of −85.9° or 2.34 ​mF ​cm−2 and -80.6° at 120 ​Hz, which are the best reported overall performances thus far. Integrated cell is also assembled to work higher voltage for line-frequency ripple filtering, with demonstrated excellent performance. This study provides a new method and structure for developing high-performance HF-ECs.

In this work, a new kind of composite nanofiber-based strain sensor with superior electromechanical properties was fabricated by using aligned thermal plastic polyurethane (TPU) nanofibers coated with multi-wall carbon nanotubes (CNTs). In order to improve the deposition efficiency and the fastness of CNTs coating on TPU nanofibers, bio-inspired dopamine (DA) was employed to modify the surface of the TPU nanofiber via a fast deposition method. (The composite nanofibers obtained were denoted as DATPU.) The electromechanical tests showed that DATPU/CNTs nanofiber membrane had a wide linear working range of 370% in the direction parallel to the nanofibers (P-DATPU/CNTs), a high gauge factor of 22.0 and a high linear coefficient of determination (r2) of 0.997. P-DATPU/CNTs nanofibers also exhibited excellent durability during stretching–releasing test for 5000 cycles. The P-DATPU/CNTs composite nanofibers demonstrated high sensing performance in detecting human motions of finger and elbow bendings.

With its unique features, lithium sulfide (Li2S) has been investigated as the cathode material for next-generation rechargeable batteries. Even though Li2S itself cannot solve all the problems faced by lithium-sulfur batteries (LSBs) and it may also introduce new issues, it does provide new opportunities. As the fully lithiated state of sulfur, Li2S offers the prospect of lithium-metal-free anodes and will also alleviate the volume expansion issues otherwise occurred in the sulfur cathode. Perhaps a most radical change when substituting sulfur with Li2S lies at the high-temperature process ability of the latter, thus opening new avenues to construct rationally designed electrodes. Despite sharing certain similarities with sulfur-based LSB, Li2S-based has its own opportunities and challenges in term of material synthesis, electrode fabrication, cell construction, and electrochemical behavior. To advance its state of the art, this review article discusses the current understandings on the initial Li2S activation process, which plays a crucial role in guiding Li2S nanostructure design and fabrication. With this leading thread, the article surveys impactful works on producing Li2S nanoparticles, encapsulating Li2S nanoparticles, simultaneously producing and encapsulating Li2S nanoparticles, and fabricating Li2S cathodes, followed by constructing lithium-metal-free LSBs. The pros and cons of different methods and the associated electrochemical behaviors are highlighted. Throughout, we call out the important research opportunities and challenges, both scattered out in the survey and aggregated in our conclusion perspective on future works, towards the fundamental understanding and practical development of Li2S-based LSBs.

High-frequency electrochemical capacitors or electrical double layer capacitor (HF-ECs) with large capacitance were developed from edge-oriented graphene (EOG) nanosheets perpendicularly grown around carbonized cellulose microfiber (CMF) sheets. Binder-free EOG/CMF electrodes were fabricated in a one-step 5-min plasma-enhanced chemical vapor deposition process, where cellulose fiber sheets were rapidly pyrolyzed by high-temperature plasma, while EOG simultaneously formed on the developing CMFs. Owing to combined unique characteristics of both EOG and CMF, such facilely produced electrodes exhibit excellent performance in terms of both high frequency response and high capacitance density. In aqueous electrolyte cells, 10 μm thick EOG/CMF electrode exhibits an areal capacitance of 1.07 mF cm−2 at 120 Hz along with a frequency of 13.8 kHz at −45° phase angle. ∼3 V organic electrolyte cells show an areal capacitance of 0.49 mF cm−2 at 120 Hz, and a frequency of 1.47 kHz at −45° phase angle. Developed HF-ECs were successfully applied in practical applications as ripple current filter in line-frequency AC/DC conversion, and as pulse power storage/smoother in environmental energy harvesting for self-powered micro devices.

Design and construction of multiphase nanostructures of metal organic frameworks (MOF) has recently been considered an effective method for the preparation of synergistic and excellent performance supercapacitor materials. Herein, Ni-Co-Mn-based metal organic frameworks (Ni-Co-Mn MOF) are prepared through an effortless one-step hydrothermal method, in which multiple metal nodes were evenly distributed between MOF nanostructure through ligands and formed a multiphase nanostructure through synergy. The synthesized Ni-Co-Mn0.25 MOF exhibits a prominent specific capacitance of 1575 F g−1 at 1 A g−1, remarkable rate capability and cycling stability. Moreover, we constructed an asymmetrical supercapacitor, which performed an excellent energy density of 73.56 Wh kg−1 at a power density of 399 W kg−1 and great cycling stability with 81.64% of original capacitance after 5000 cycles. Ni-Co-Mn MOF is a promising hybrid electrode material for excellent performance supercapacitor as well as it provides a simple and economic way to fabricate supercapacitor composite materials.

With good operation flexibility and scalability, vanadium redox-flow batteries (VRBs) stand out from various electrochemical energy storage (EES) technologies. However, traditional electrodes in VRBs, such as carbon and graphite felt with low electrochemical activities, impede the interfacial charge transfer processes and generate considerable overpotential loss, which significantly decrease the energy and voltage efficiencies of VRBs. Herein, by using a facile electrodeposition technique, Prussian blue/carbon felt (PB/CF) composite electrodes with high electrochemical activity for VRBs are successfully fabricated. The PB/CF electrode exhibits excellent electrochemical activity toward VO2+ /VO2 + redox couple in VRB with an average cell voltage efficiency (VE) of 90% and an energy efficiency (EE) of 88% at 100 mA cm-2 . In addition, due to the uniformly distributed PB particles that are strongly bound to the surface of carbon fibers in CF, VRBs with the PB/CF electrodes show much better long-term stabilities compared with the pristine CF-based battery due to the redox-mediated catalysis. A VRB stack consisting of three single cells (16 cm2 ) is also constructed to assess the reliability of the redox-mediated PB/CF electrodes for large-scale application. The facile technique for the high-performance electrode with redox-mediated reaction is expected to shed new light on commercial electrode design for VRBs.

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Advanced microscopy and/or spectroscopy tools play indispensable roles in nanoscience and nanotechnology research, as they provide rich information about material processes and properties. However, the interpretation of imaging data heavily relies on the “intuition” of experienced researchers. As a result, many of the deep graphical features obtained through these tools are often unused because of difficulties in processing the data and finding the correlations. Such challenges can be well addressed by deep learning. In this work, the optical characterization of 2D materials is used as a case study, and a neural-network-based algorithm is demonstrated for the material and thickness identification of 2D materials with high prediction accuracy and real-time processing capability. Further analysis shows that the trained network can extract deep graphical features such as contrast, color, edges, shapes, flake sizes, and their distributions, based on which an ensemble approach is developed to predict the most relevant physical properties of 2D materials. Finally, a transfer learning technique is applied to adapt the pretrained network to other optical identification applications. This artificial-intelligence-based material characterization approach is a powerful tool that would speed up the preparation, initial characterization of 2D materials and other nanomaterials, and potentially accelerate new material discoveries.

To obtain magnetorheological elastomers (MREs) with improved mechanical properties and exhibiting an enhanced magnetorheological (MR) effect, bio-inspired dopamine modification has been used to improve the functionality at the surface of carbonyl iron (CI) particles. Various techniques including x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to confirm that a polydopamine (PDA) layer of about 27.5 nm had been successfully deposited on the surface of the carbonyl iron particles prior to their inclusion in the MRE composites. The magnetic properties of PDA modified CI particles were shown to be almost the same as those for untreated CI particles. With the introduction of a PDA layer to the surfaces of the particles, both the tensile strength and the elongation at break of the MREs were improved. Furthermore, the MRE composites filled with PDA-coated CI particles exhibited lower zero-field storage moduli but higher magnetic field induced storage moduli when magnetization saturation was reached. The absolute and relative MR effect for the MREs reached 0.68 ± 0.002 MPa and 294% respectively, which were higher than those of MREs with pristine CI particles whose absolute and relative MR effect were 0.57 ± 0.02 MPa and 187% respectively. The findings of this work provide insights into enhanced fabrication of MREs with both improved mechanical properties and magneto-induced performance.

The high cost and limited reserves of noble metals such as Pt have hampered their large-scale commercial applications in the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Herein, we developed a simple silica template approach to form porous carbons codoped with nitrogen and cobalt as highly efficient bifunctional electrocatalysts for the ORR and HER. The resulting porous carbons exhibited excellent electrocatalytic activity for the ORR in alkaline media, which compares favorably with that of commercial Pt/C (20 wt%), and had superior durability and excellent methanol tolerance. The porous carbons also showed superior performance for the HER, with a low onset potential of −0.04 V, a Tafel slope of 49 mV dec−1, an overpotential of −0.106 V at a current density of 10 mA cm−2, and remarkable durability. These results demonstrate that the Co, N-doped carbons are promising bifunctional catalysts for fuel cell applications.

There is strong interest in developing high-frequency (HF) supercapacitors or electrochemical capacitors (ECs), which can work at the hundreds to kilo hertz range for line-frequency alternating current (AC) filtering in the substitution of bulky aluminum electrolytic capacitors, with broad applications in the power and electronic fields. Although great progress has been achieved in the studies of electrode materials for ECs, most of them are not suitable to work in this high frequency range because of the slow electrochemical processes involved. Edge-oriented vertical graphene (VG) networks on 3D scaffolds have a unique structure that offers straightforward pore configuration, reasonable surface area, and high electronic conductivity, thus allowing the fabrication of HF-ECs. Comparatively, highly conductive freestanding cross-linked carbon nanofibers (CCNFs), derived from bacterial cellulose in a rapid plasma pyrolysis process, can also provide a large surface area but free of rate-limiting micropores, and are another good candidate for HF-ECs. In this mini review, advances in these fields are summarized, with emphasis on our recent contributions in the study of these materials and their electrochemical properties including preliminary demonstrations of HF-ECs for AC line filtering and pulse power storage applications.

Compared with traditional methods for preparing dielectric elastomer (DE) films, electrohydrodynamic (EHD) 3D printing displays many advantages, notably full automation, computer control and flexible design. It also confers high printing resolution, high preparation efficiency with minimal probability of nozzle clogging. In this article, EHD 3D printing was employed to fabricate silicone rubber (SR) based DE films. In order to increase their dielectric constant, high dielectric copper phthalocyanine (CuPc) particles were added into the SR ink. Optimal printing conditions were determined by analyzing the effects of printing voltage and ink properties on the formation of liquid cone and the printed line width. The SR/CuPc composite film with 3 wt% CuPc particles (SR/CuPc-3) exhibits a high dielectric constant of 5.52, with a large actuated area strain of 23.7% under an electric field of 39.4 V μm−1. Furthermore, under 100 cycles of electric field loading, SR/CuPc-3 demonstrate excellent electromechanical stability, indicating that EHD 3D printing holds a considerable potential for fabricating high-performance DE films in an efficacious manner.

Cu–Ni–Mn-based ternary P2-type NaxCu0.15Ni0.20Mn0.65O2 (x = 0.50, 0.67, and 0.75) cathodes for sodium-ion batteries (SIBs) are synthesized by a co-precipitation method. We find that Na content plays a key role on the structure, morphology, and the charge–discharge performances of these materials. For x = 0.67 and 0.75, superstructure from Na+-vacancy ordering is observed, while it is absent in the x = 0.50 sample. Despite the same synthesis conditions, materials with x = 0.67 and 0.75 show smaller particle sizes compared to that of the x = 0.50 sample. In addition, redox potentials of the materials differ significantly even though they have the same transition metal ratios. These differences are attributed to the changes in local structures of the as-prepared materials arising from the different amount of Na and possibly oxygen in the lattice. Materials with x = 0.67 and 0.75 show excellent rate performance and cycle stability when tested as cathode material of SIBs. Average discharge potential is as high...

Interconnected porous FeS/C composite consisting of FeS nanoparticles (∼20 nm) homogeneously embedded in carbon nanosheets was synthesized via a facile freeze-drying/carbonization method using a NaCl template. As an anode for LIBs, this composite shows significantly enhanced electrochemical performance due to the synergistic effects of the conductive carbon film and the porous structure, which provides an ideal conductive matrix and buffer spaces for electron/ion transfer and FeS expansion, respectively, during lithiation processes. This composite exhibits reversible capacities of ∼703 mA h g−1 over 150 cycles at 1 A g−1 and a high-rate capability of ∼530 mA h g−1 even at 5 A g−1, which is among the best reported electrochemical performances for FeS-based materials thus far. With a long cycling life and high power density, this composite demonstrates its potential application in LIBs.

Exosomes, nanoscale extracellular vesicles functioning as cell-to-cell communicators, are an emerging promising therapeutic in the field of bone tissue engineering. Here, we report the construction and evaluation of a novel cell-free tissue-engineered bone that successfully accelerated the restoration of critical-sized mouse calvarial defects through combining exosomes derived from human adipose-derived stem cells (hASCs) with poly(lactic-co-glycolic acid) (PLGA) scaffolds. The exosomes were immobilized on the polydopamine-coating PLGA (PLGA/pDA) scaffolds under mild chemical conditions. Specifically, we investigated the effects of hASC-derived exosomes on the osteogenic, proliferation, and migration capabilities of human bone marrow-derived mesenchymal stem cells in vitro and optimized their osteoinductive effects through osteogenic induction. Furthermore, an in vitro assay showed exosomes could release from PLGA/pDA scaffold slowly and consistently and in vivo results showed this cell-free system enhanced bone regeneration significantly, at least partially through its osteoinductive effects and capacities of promoting mesenchymal stem cells migration and homing in the newly formed bone tissue. Therefore, overall results demonstrated that our novel cell-free system comprised of hASC-derived exosomes and PLGA/pDA scaffold provides a new therapeutic paradigm for bone tissue engineering and showed promising potential in repairing bone defects.

Here we report a hierarchical composite structure composed of few-layers molybdenum disulfide nanosheets supported by vertical graphene on conductive carbon cloth (MDNS/VG/CC) for high-performance electrochemical hydrogen evolution reaction (HER). In the fabrication, 3D vertical graphene is first prepared on carbon cloth by a micro-wave plasma enhanced chemical vapor deposition (MPCVD) and then few-layers MoS 2 nanosheets are in-situ synthesized on the surface of the vertical graphene through a simple hydrothermal reaction. This integrated catalyst exhibits an excellent HER electrocatalytic activity including an onset potential of 50 mV, an overpotential at 10 mA cm −2 ( η 10 ) of 78 mV, a Tafel slop of 53 mV dec −1 , and an excellent cycling stability in acid solution. The excellent catalytic performance can be ascribed to the abundant active edges provided by the vertical MoS 2 nanosheets, as well as the effective electron transport route provided by the graphene arrays on the conductive substrate. Moreover, the vertical graphene offers robust anchor sites for MoS 2 nanosheets and appropriate intervals for electrolyte infiltration. This not only benefits hydrogen convection and release but also avoids the damaging or restacking of catalyst in electrochemical processes.

FeMoO4 nanorods were synthesized by a one-step solvothermal method and demonstrated to have attractive performance as an anode material in lithium ion batteries (LIBs). The specific capacity of the electrode exhibited an initial fading in the first 50 cycles and subsequently recovered to 1265 mA h g−1 at about the 500th cycle at a rate of 1C, after that, the capacity remained stable around 1110 mA h g−1 until the 1000th cycle. Based on comprehensive analysis of the structural and chemical evolution at each stage of capacity variation, we illustrated that the FeMoO4 nanorods were converted to a Fe2O3/MoO3 mixture after the first cycle and they experienced gradual structural variation of grain refinement and amorphization with their morphology transformed from nanorods to nanosheets upon cycling. Such changes in the chemical composition and microstructure of nanorods led to larger effective surface area, improved electrochemical reaction kinetics, and capacity retention capability. As a similar tendency of the specific capacity upon cycling has been widely observed for metal oxide anodes, studies on structural and chemical evolution of electrode materials during the whole cyclic life will be helpful for understanding their electrochemical reaction mechanism and provide guidance to material design and structural optimization of electrodes.

The extensive volume change and continuous consumption of active electrode materials due to the repeated formation of a solid electrolyte interface (SEI) layer during charge–discharge cycles are two important topics to be considered for the development of new nanostructured electrodes for high-performance lithium ion batteries (LIBs). In this work, layer-stacked cobalt ferrite (CoFe2O4) mesoporous platelets with two different thicknesses are synthesized, and their electrochemical performance as anodes for LIBs is evaluated. We find that the thickness of the platelets has a great impact on the specific capacity and stability. The thicker platelets (∼2 μm) enable a reduction of SEI-induced consumption of active materials and lead to an overall electrochemical performance superior to that of thinner ones. At a high rate of 5 A g−1, after an initial drop, the capacity of thicker platelets continuously increases in the following 500 cycles and reaches saturation around 950 mA h g−1, then gradually decreases and remains at 580 mA h g−1 after 2000 cycles. The high capacitance, outstanding rate performance and stability of thick platelets can be attributed to the special configuration of the layer-stacked mesoporous platelets which provides sufficient interlayer space for volume expansion, and enables the formation of a stable SEI layer during the cycling.

In this paper, nanostructured porous MnCO3 spheres are facilely synthesized, which can simultaneously provide an increased surface for conversion reaction and capacitive storage as the anode material for lithium ion batteries. This material gives a superior specific capacity and excellent long-term cycling performance even at a high current density. It can deliver a stable capacity of 1049 mA h g(-1) after 200 cycles at a current density of 1000 mA g(-1), which is much higher than the theoretical capacity of 466 mA h g(-1). After 2000 cycles at a high current density of 5000 mA g(-1), a capacity of 510 mA h g(-1) can still be maintained. Their high rating performance at 5000 mA g(-1) is among the best-reported performances of anode materials. From the in situ or ex situ SEM observation, the porous MnCO3 nanostructure can provide a stable template for reversible lithium insertion and extraction without significant morphology change and accommodate the volume change during the charge-discharge process. Also this structure increases the capacitive contribution to the total capacity compared with other MnCO3 samples.

While sodium-ion batteries (SIBs) are considered as a next-generation energy storage device because of the higher abundance and lower cost of sodium compared to those of lithium, developing high-power and stable cathode materials remains a great challenge. Here, micron-sized plate-like copper-substituted layered P2-type Na0.67CuxMn1−xO2 is demonstrated to rapidly charge and discharge within 5 minutes while giving a capacity of more than 90 mA h g−1, corresponding to a half-cell energy density of 260 W h (kg cathode)−1 at a power density of 3000 W (kg cathode)−1, which is comparable to that of high-power lithium-ion cathodes. The materials show excellent stability, retaining more than 70% of the initial capacity after 500 cycles at 1000 mA g−1. The good cycle and rate performances of the materials are attributed to copper in the lattice, which stabilizes the crystal structure, increases the average discharge potential and improves sodium transport. This makes Na0.67CuxMn1−xO2 an ideal choice as a cathode for high-power sodium-ion batteries.

Due to its high theoretical capacity and low lithium insertion voltage plateau, silicon has been considered one of the most promising anodes for high energy and high power density lithium ion batteries (LIBs). However, its rapid capacity degradation, mainly caused by huge volume changes during lithium insertion/extraction processes, remains a significant challenge to its practical application. Engineering Si anodes with abundant free spaces and stabilizing them by incorporating carbon materials has been found to be effective to address the above problems. Using sodium chloride (NaCl) as a template, bubble sheet-like carbon film supported core-shell Si/C composites are prepared for the first time by a facile magnesium thermal reduction/glucose carbonization process. The capacity retention achieves up to 93.6% (about 1018 mAh g(-1)) after 200 cycles at 1 A g(-1). The good performance is attributed to synergistic effects of the conductive carbon film and the hollow structure of the core-shell nanospheres, which provide an ideal conductive matrix and buffer spaces for respectively electron transfer and Si expansion during lithiation process. This unique structure decreases the charge transfer resistance and suppresses the cracking/pulverization of Si, leading to the enhanced cycling performance of bubble sheet-like composite.

Silicon materials are considered as the new generation of high specific energy and energy density anodes for rechargeable lithium ion batteries, but the silicon pulverization during lithium insertion hinders their commercial implementation. Although extensive effort has been put on addressing these problems, the microstructure of the silicon material still needs to be well engineered in order to improve the stability of the anode materials and simplify the synthesis procedure using a scalable and easy available silicon source without any toxicity. In this work, a novel hollow nanosphere with Si/SiOx nanoparticles incompactly distributed within a spherical carbon shell was successfully fabricated via a facile in situ carbonization/reduction method. With enhanced electrode conductivity and sufficient free space for silicon expansion during the lithiation process, this material shows much better cycle life and rate capability than directly reduced silicon nanoparticles.

Electrochemically reduced graphene oxides (ERGO) are obtained under various reducing potentials in the phosphate buffer solution (PBS). Different characterization methods are used to analyse the changes of structure and surface chemical condition for graphene oxide (GO). The results show that GO could be reduced controllably to certain degree and its electrochemical activity towards VO2+/VO2+ and V3+/V2+ redox couples is also tunable using this environmentally friendly method. The catalytic mechanism of the ERGO is discussed in detail, the C O functional groups other than the C–O functional groups on the surface of ERGO more likely provide reactive sites for those redox couples, leading to a more comprehensive understanding about the catalytic process than previous relevant researches. This controllable modification method and the ERGO as electrode reaction catalyst with enhanced battery performance are supposed to have promising applications in the all vanadium redox flow battery.

Different modified multiwalled carbon nanotubes (MWCNTs) are prepared by heat treatments in the air and in the H2SO4 + HNO3 (1:1) mixed acids which are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Brunaur–Emmett–Teller, and cyclic voltammetry measurements. The results show the physicochemical properties of MWCNTs change significantly after these different modification processes, especially the electrochemical catalytic activity towards the VO2 +/VO2+ and V3+/V2+ redox pairs. The MWCNTs treated in the air at 600 °C for 30 min shows better electrochemical performances for the VO2 +/VO2+ redox reactions (58.8 and −32.4 μA for the oxidation and reduction peaks at 10 mV s−1, respectively) than any other samples. Compared with the V3+/V2+ redox couple, the VO2 +/VO2+ redox reactions are more easily affected by the physicochemical property changes of the MWCNTs. The enhanced electrochemical catalytic activity of the modified MWCNTs is not only related to the surface oxygen content, but also to the specific surface area, conductivity and the unique structure variations of the MWCNTs. The investigation demonstrated that the modified MWCNTs have a promising future application in the vanadium redox flow battery.

3D graphene‐nanowall‐decorated carbon felts (CF) are synthesized via an in situ microwave plasma enhanced chemical vapor deposition method and used as positive electrode for vanadium redox flow battery (VRFB). The carbon fibers in CF are successfully wrapped by vertically grown graphene nanowalls, which not only increase the electrode specific area, but also expose a high density of sharp graphene edges with good catalytic activities to the vanadium ions. As a result, the VRFB with this novel electrode shows three times higher reaction rate toward VO2 +/VO2+ redox couple and 11% increased energy efficiency over VRFB with an unmodified CF electrode. Moreover, this designed architecture shows excellent stability in the battery operation. After 100 charging–discharging cycles, the electrode not only shows no observable morphology change, it can also be reused in another battery and practical with the same performance. It is believed that this novel structure including the synthesis procedure will provide a new developing direction for the VRFB electrode.

Pristine multi-walled carbon nanotubes (MWCNTs), and those functionalized with hydroxyl groups, or carboxyl groups were used as electrode reaction catalyst for VO(2)(+)/VO(2+) redox couples for vanadium redox flow battery. The structure, composition, electrochemical properties and battery performance were characterized with scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry and cell charge-discharge tests. The electrochemical activities of the redox couple are greatly increased over those of modified glassy carbon electrodes and the electrocatalytic kinetics of the redox reactions are in the order of carboxyl MWCNTs > hydroxyl MWCNTs > pristine MWCNTs. The peak currents of the redox reactions (63.8 and -51.1 mu A for oxidation and reduction processes, respectively) on the electrode modified by carboxyl MWCNTs are about three times those for the other electrodes. The battery exhibits excellent storage efficiency when the carboxyl MWCNTs were used as positive electrode reaction catalyst, suggesting the oxygen functional groups especially the carboxyl can significantly facilitate the VO(2)(+)/VO(2+) redox reactions. (C) 2011 Elsevier Ltd. All rights reserved.

Surface and planar defect structures of γ-Al2O3 nanorods synthesized by the arc-discharge method were studied by means of high-resolution transmission electron microscopy and image simulation. Our investigation showed that there was a high number density of twins in the nanorods. We suggested a possible configuration of {111} twins in γ-Al2O3, and this model fit our experimental result well. In some nanorods, the ordering of nanotwins gave rise to a local hexagonal-like structure. The twinned nanorods were usually enclosed by {100} and {111} facets, and their growth direction was changed from 〈110〉 into 〈111〉. The surface structures of the nanorods confirmed that the {111}-type surface should be more stable.

The electronic transport properties as a function of temperature and the graphite content have been investigated for disordered PbO2-Ag2O-xC (0

Porous hierarchical NiMn2O4/C tremella-like nanostructures are obtained through a simple solvothermal and calcination method. As the anode of lithium ion batteries (LIBs), porous NiMn2O4/C nanostructures exhibit a superior specific capacity and an excellent long-term cycling performance even at a high current density. The discharge capacity can stabilize at 2130 mA h g(-1) within 350 cycles at a current density of 1000 mA g(-1). After a long-term cycling of 1500 cycles, the capacity is still as high as 1773 mA h g(-1) at a high current density of 4000 mA g(-1), which is almost five times higher than the theoretical capacity of graphite. The porous NiMn2O4/C hierarchical nanostructure provides sufficient contact with the electrolyte and fast three-dimensional Li(+) diffusion channels, and dramatically improves the capacity of NiMn2O4/C via interfacial storage.

Honeycomb-like mesoporous pyrite FeS2 microspheres, with diameters of 500-800 nm and pore sizes of 25-30 nm, are synthesized by a simple solvothermal approach. The mesoporous FeS2 microspheres are demonstrated to be an outstanding counter electrode (CE) material in quantum dot sensitized solar cells (QDSSCs) for electrocatalyzing polysulfide electrolyte regeneration. The cell using mesoporous FeS2 microspheres as CE shows 86.6% enhancement in power conversion efficiency (PCE) than the cell using traditional noble Pt CE. Furthermore, it also shows 11.4% enhancement in PCE than the cell using solid FeS2 microspheres as CE, due to the mesoporous structure facilitating better contact with polysulfide electrolyte and fast diffusion of redox couple species in electrolyte.

A composite of porous CuCo2O4 nanocubes well wrapped by reduced graphene oxide (rGO) sheets has been synthesized by a facile microwave-assisted solvothermal reaction and applied as anode in lithium ion batteries (LIBs). The porous structure of the CuCo2O4 nanocubes not only provides a high surface area for contact with the electrolyte, but also assists by accommodating volume change upon charging-discharging. Impedance measurements and transmission electron microscopy show that incorporation of rGO further decreases the charge transfer resistance and improves the structural stability of the composite. As an anode material for a LIB, the composite exhibits a high stable capacity of ∼ 570 mA h g(-1) at a current density of 1000 mA g(-1) after 350 cycles. With a high specific surface area and a low charge transfer resistance, the composite anode shows impressive performance especially at high current density. The LIB shows a high capacity of ∼ 450 mA h g(-1) even at a high current density of 5000 mA g(-1), demonstrating the composite's potential for applications in LIBs with long cycling life and high power density.

The boron-nitride (BN) nanocages are synthesized by nitrogenation of amorphous boron nanoparticles at 1073 K under nitrogen and ammonia atmosphere. The BN nanocages exhibit a well-crystallized feature with nearly pentagonal or spherical shape, depending on their size. High-resolution transmission electron microscopy studies reveal that they are hollow nanocages. The growth mechanism of the BN nanocages is proposed.