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Polyacrylamide hydrogel electrolytes with highly concentrated salt solutions have been developed for solid-state supercapacitors of slow self-discharge. When the supercapacitors are charged by a triboelectric nanogenerator, a much enhanced charging efficiency has been obtained.

Lithium-ion capacitors (LICs) are assembled with lithium titanate nanoparticles embedded in mesoporous carbon spheres (n-LTO@MC) as anodes and activated carbon (AC) as cathodes. The resulting AC//n-LTO@MC capacitors exhibit excellent high-rate capacities of 155 and 79 mAh g−1 at current rates of 100 and 1000 C, respectively. Charging the ultrafast LICs by rotating triboelectric nanogenerator (R-TENG) with pulsed output at high frequencies is investigated and compared with LICs based on low-rate LTO nanoparticles (AC//n-LTO) and commercial LTO (AC//c-LTO). Shorter charging times by R-TENG rotating at various revolutions and larger discharging specific capacities are demonstrated for AC//n-LTO@MC than AC//n-LTO and AC//c-LTO LICs. The improved efficiency of AC//n-LTO@MC for storing energy generated by R-TENG indicates that ultrafast LICs are promising energy storage devices that may be combined with TENGs as self-charging power unit for harvesting ambient mechanical energy and powering portable electronic devices and remote sensors.

Triboelectric nanogenerators (TENG) are mechanical energy harvesting devices with pulsed output at frequencies ranging from a few to hundreds of hertz. Supercapacitors (SCs) are ideal energy storage devices for TENGs because of their high specific capacitance and excellent cycling performance, except that the poor high-frequency response of conventional supercapacitors limits their capability for storing pulsed energy at high frequencies. In this work, via a simple high-temperature carbonization process, we have fabricated carbonized melamine foams as electrode materials for high-frequency supercapacitors (HF-SCs). The resulting HF-SCs with a phase angle of − 80.1° and a specific areal capacitance of 132 μF cm−2 at 120 Hz were successfully employed as alternating current (ac) line filter for smoothing ripple current. When charged with a rotating TENG (R-TENG), the HF-SCs exhibited an energy utilization efficiency that is 20.3% higher than conventional activated carbon-based SCs, demonstrating the advantage of HF-SCs for storing pulsed energy generated by TENGs.

Single-atom catalysis is a new frontier in the heterogeneous catalysis field due to its high activity and selectivity for various catalytic reactions. However, decades ago, single-atom catalysts could not be clearly visualized and characterized due to limitations associated with instrument resolution. In recent years, with the rapid development of characterization techniques, high-resolution scanning tunneling microscopy (STM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and other characterization techniques have been used to accurately represent single-atom catalysts. In this review, we discuss in depth these characterization techniques for Pt single-atom catalysts and focus on Fourier transformed EXAFS spectroscopy to study the coordination environment of Pt–M (M = Cl, O, C, N, S, Pt, Cu, Pd, Ni, Fe) for atomically dispersed Pt catalysts on diverse supports. We believe that this review will lead to better understanding of the effective characterization of Pt single-atom catalysts and promote further research on Pt single-atom catalysis in the future.

Prussian blue (PB) and its analogues (PBAs) are promising cathode materials for sodium ion batteries (SIBs) because of their wide diffusion tunnels for sodium ions. However, water molecules typically contained within PB structures have been hypothesized to undermine their stability and rate performance. Here we report that zeolite water molecules in PB structures may induce the formation of Na2CO3 as one of the main components in SEI layer on the surface of PB materials. From PB samples containing zeolite water synthesized via a solvothermal method at different temperatures, a specific capacity of 113 mAh g−1 is demonstrated at 10 mA g−1, with a capacity retention of 75% at 1000 mA g−1. Cycling tests reveal a capacity loss of only 1.2% after 100 cycles at 200 mA g−1. It is suggested that Na2CO3 contained in the SEI layer not only protects the electrode materials from side reactions with the electrolyte, but also facilitates quick charge transfer at the interfaces, leading to improved electrochemical performances.

For electric double layer capacitors (EDLCs, or supercapacitors), self-discharge has been an inevitable issue that causes decay of cell voltage and loss of stored energy, but this problem has long been ignored in the studying of supercapacitors. Due to self-discharge, applications of supercapacitors for long-term energy storage or collecting environmental energy harvested by small power devices have been severely limited. There are three main self-discharge processes for EDLCs, including i) charge diffusion and redistribution, ii) faradaic reactions, and iii) ohmic leakage. In this work, we introduced a nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) as an additive to the electrolyte to suppress the self-discharge of EDLCs. When the EDLCs are charged, the electric field in the double layers near the electrode surface induces alignment of 5CB molecules, causing much enhanced fluid viscosity via the so-called electrorheological (ER) effect. As a result, the diffusion of ions and redox species in the electrolyte can be impeded and the self-discharge rate can be reduced. Here, we have demonstrated that by adding 2% of 5CB in TEMABF4/acetonitrile electrolyte, the decay rate of open circuit potential and leakage current can be reduced by more than 80%. Simulation results confirmed the reduced contribution of both diffusion of ions and faradaic reactions to the overall self-discharge. Furthermore, when 5CB EDLCs were employed for storing energy harvested by a triboelectric nanogenerator (TENG) that has a characteristic of pulsed output current, much enhanced charging efficiency was attained compared to EDLCs without 5CB. Our study pointing to a feasible way for truly pushing supercapacitor for practical applications.

Silicon has proved to be a promising anode material of high-specific capacity for the next-generation lithium ion batteries (LIBs). However, during repeated discharge/charge cycles, Si-based electrodes, especially those in microscale size, pulverize and lose electrical contact with the current collectors due to large volume expansion. Here, we introduce a general method to synthesize Cu@M (M = Si, Al, C, SiO2, Si3N4, Ag, Ti, Ta, SnIn2O5, Au, V, Nb, W, Mg, Fe, Ni, Sn, ZnO, TiN, Al2O3, HfO2, and TiO2) core–shell nanowire arrays on Cu substrates. The resulting Cu@Si nanowire arrays were employed as LIB anodes that can be reused via HCl etching and H2-reduction. Multishelled Cu@Si@Cu microparticles supported on 3D Cu current collectors were further prepared as stable and binder-free LIB anodes. This 3D Cu@Si@Cu structure allows the interior conductive Cu network to effectively accommodate the volume expansion of the electrode and facilitates the contact between the Cu@Si@Cu particles and the current collector...

For supercapacitors, high self-discharge rate is an inevitable issue that causes fast decay of cell voltage and loss of stored energy. Designing supercapacitors with suppressed self-discharge for long-term energy storage has been a challenge. In this work, we demonstrate that substantially reduced self-discharge rate can be achieved by using highly concentrated electrolytes. Specifically, when supercapacitors with 14 M LiCl electrolyte are charged to 0.80 V, the open circuit voltage (OCV) drops to 0.65 V in 24 h. In stark contrast, when the electrolyte concentration is reduced to 1 M, the OCV drops from 0.80 to 0.65 V within only 0.3 h, which was 80 times faster than that with 14 M LiCl. Decreased OCV decay rate at high electrolyte concentration is also confirmed for supercapacitors with different electrolytes (e.g., LiNO3) or at higher charging voltages (1.60 V). The slow self-discharge in highly concentrated electrolyte can be largely attributed to impeded electron transfer between the electrodes and electrolyte due to the formation of hydration clusters and reduced amount of free water molecules, thereby faradaic reactions that cause fast self-discharge are reduced. Our study not only supports the newly revised model about the formation of electric double layer with the inclusion of electron transfer, but also points a direction for substantially reducing the self-discharge rate of supercapacitors.

Self-discharge is an important factor to be considered for practical applications of supercapacitors (SCs). While the transport of electrolyte ions largely determines the rate performance of SCs, it also affects their self-discharge rate. In this work, three carbon materials, namely stacking carbon nanosheets (S-CNSs), double-layer carbon nanosheets (DL-CNSs), and flower-like carbon nanosheets (FL-CNSs), with similar pore sizes but different pore structures were synthesized. Due to the different pore structures and correspondingly different ion transport resistances, the rate performances increased from S-CNS, FL-CNS, to DL-CNS SCs. On the other hand, the self-discharge rates increased following the same order – the open circuit voltage dropped from 2.0 to 0.99, 0.74, and 0.53 V after 24 h for S-CNS, FL-CNS, and DL-CNS SCs, respectively. Analysis of the self-discharge processes indicates a combined diffusion-controlled and ohmic leakage self-discharge mechanism and a larger diffusion constant was found for DL-CNS than that of FL-CNS and S-CNS SCs, consistent with their order of self-discharge rates. The results of this work suggest that although fast ion transport is beneficial to the rate performance of SCs, it may also lead to fast self-discharge and limit the duration of energy storage.

We designed and synthesized CuO/SnO2/Pd hollow microboxes, which was developed based on prepared Cu2O cubes coated Pd nanosheets, controlled oxidation of Cu2O/Pd, and etching of Cu2O/CuO/Pd by SnCl4 solution. The catalytic property of the Cu2O, Cu2O/SnO2, Cu2O/Pd/SnO2, Cu2O/Pd, Cu2O/CuO/Pd, CuO/SnO2/Pd, CuO, and commercial catalyst for dimethyldichlorosilane synthesis via the Rochow reaction was investigated. As compared to control samples and commercial catalyst, the prepared CuO/Pd/SnO2 hollow microboxes exhibited much higher silicon conversion (76.6%), which is related to the synergistic effect between CuO, Pd and SnO2, and to the distinct catalyst hollow structure which allows the efficient transportation of the reactant molecules to the active component.

The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a systematic and feasible strategy to synthesize Cu2O solid spheres and hexahedrons by controlling the diffusion coefficients. These Cu2O products can be successively transformed into corresponding Cu hollow spheres and hexahedrons as well as CuO porous spheres and hexahedrons by controlling hydrogen diffusion in hydrazine hydrate solution and controlling oxygen diffusion in air, respectively. The formation of these transformations was also discussed in detail. Tested for Rochow reaction, the as-prepared Cu2O solid and CuO porous spheres exhibit higher dimethyldichlorosilane selectivity and Si conversion than Cu hollow spheres, which is attributed to the active sites for CH3Cl adsorption formed in Cu x Si phase after the removal of oxygen atoms in Cu2O and CuO in the formation of dimethylchlorosilane. The present work not only develops a feasible method for preparing well shape-defined Cu2O solid spheres and hexahedrons but also clarifies the respective roles of Cu, Cu2O and CuO in dimethyldichlorosilane synthesis via Rochow reaction.

Coal-fired power plants represent the largest source of mercury emissions worldwide. Using fly ash, a byproduct of these plants, as a sorbent to remove mercury has proven to be difficult. Here, we found that the fresh surface of modified fly ash has good adsorption performance, and it declines obviously with time because of unsaturation characteristics on surface. On the basis of this mechanism, our study provides a method to in situ capture mercury with high surface energy modified fly ash by mechanochemical and bromide treatment. Fresh modified fly ash with active sites is injected into the flue to directly adsorb mercury. A continuous system within a full-scale 300 MWe plant showed that the mercury adsorption performance of the modified fly ash is similar to that of activated carbon, which is the industry benchmark for the treatment of mercury emission in fossil power generation units. This is a breakthrough and indicates that modified fly ash can become an efficient and convenient industrial sorbent for the removal of mercury.

A series of copper catalysts with a core–shell or tubular structure containing various contents of Cu, Cu2O, and CuO were prepared via controlled oxidation of Cu nanowires (NWs) and used in the synthesis of dimethyldichlorosilane (M2) via the Rochow reaction. The Cu NWs were prepared from copper (II) nitrate using a solution-based reduction method. The samples were characterized by X-ray diffraction, thermogravimetric analysis, temperature-programmed reduction, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. It was found that the morphology and composition of the catalysts could be tailored by varying the oxidation temperature and time. During the gradual oxidation of Cu NWs, the oxidation reaction initiated on the outer surface and gradually developed into the bulk of the NWs, leading to the formation of catalysts with various structures and layered compositions, e.g., Cu NWs with surface Cu2O, ternary Cu–Cu2O–CuO core–shell NWs, binary Cu2O–CuO nanotubes (NTs), and single CuO NTs. Among these catalysts, ternary Cu–Cu2O–CuO core–shell NWs exhibited superior M2 selectivity and Si conversion in the Rochow reaction. The enhanced catalytic performance was mainly attributed to improved mass and heat transfer resulting from the peculiar heterostructure and the synergistic effect among layered components. Our work indicated that the catalytic property of Cu-based nanoparticles can be improved by carefully controlling their structures and compositions.

The self-discharge of supercapacitors was investigated using electrodes composed of multiwalled carbon nanotubes (MWCNTs) of three different diameters: 20, 30, and 50 nm, respectively. A combined self-discharge mechanism including both ohmic leakage and diffusion-controlled faradaic reaction was employed to fit the open circuit voltage (OCV) decays of the supercapacitors. The existence of both large inter-bundle pores and small intra-bundle pores in the MWCNT electrodes led to a two-stage diffusion-controlled faradaic reaction process - while the first stage can be described as a divided diffusion-controlled (DDC) process due to the diffusion of ions from both inter- and intra-bundle pores, and the second stage corresponds to a single diffusion-controlled (SDC) process mainly due to the diffusion of ions from the intra-bundle pores. The diffusion parameters obtained based on this model were consistent with the measured self-discharge rates which increased with the size of the MWCNTs. The results of this work demonstrate that electrode materials with wide pore size distributions may be associated with more complex self-discharge processes.

Despite the promising application of patterned Si wafers (PSWs) in electrochemistry and photochemistry, the simple and environment-friendly fabrication of these PSWs is still a great challenge. Herein, we report a novel method for fabrication of PSWs via Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. In this reaction, commercial Si wafers (SWs) reacted with gas CH3Cl over patterned various Cu-based catalyst to create regular patterns. PSWs were obtained after removal of Cu compounds followed with facile post treatment. Because of simplicity, low-cost and low-toxicity of this approach, the manufacture of PSWs on an industrial scale is highly possible, which can be realized by integrating the organosilane synthesis process and controlling the reaction conditions. (C) 2015 Elsevier B.V. All rights reserved.

Nowadays, how to achieve both high dimethyldichlorosilane selectivity and silicon conversion in the Rochow reaction still remains a major challenge in the organosilane industry, in which silicon and chloromethane are converted into methylchlorosilanes on Cu-based catalysts mixed with ZnO promoter. Therefore, this calls for the development of outstanding catalysts with both high activity and selectivity for the Rochow reaction and also for a deep fundamental understanding of the catalytic mechanism. In this work, we designed and synthesized a series of copper oxide–zinc oxide catalysts ((CuO)xZnO (0 ≤ x ≤ 49)) with a distinct porous hollow spherical structure for the reaction. These porous hollow spherical catalysts composed of CuO and ZnO nanoparticles were prepared through co-adsorption of Cu2+ and Zn2+ in the interior and outer surfaces of the hydrothermally synthesized carbonaceous spheres, followed by a new hydrothermal treatment and calcination in air. The catalytic properties of the (CuO)xZnO hollow spheres for dimethyldichlorosilane synthesis via the Rochow reaction was investigated, and a deeper understanding of the catalytic mechanism was obtained. As compared to pure CuO hollow spheres, the prepared (CuO)19ZnO hollow spheres exhibited much higher dimethyldichlorosilane selectivity and silicon conversion, which are clearly related to the synergistic electronic effect between Cu and ZnO and to the distinct catalyst structures which allow intimate contact of the reactant molecules with the active component and the efficient transport of the molecules. This work opens a new way for the fabrication of efficient and integrated Cu-based catalysts for the Rochow reaction.

As the most promising next-generation lithium-ion battery anode materials, porous silicon-based materials are attracting great attention nowadays, mainly because of silicon's exceptionally high lithium storage capacity. However, how to realize the large-scale manufacture of these materials at low cost still remains a big challenge. In this work, we report the direct preparation of porous Si materials from metallurgical-grade Si in an autoclave, which is the most environmentally friendly route to produce alkoxysilane monomers in the organic silicon industry. In this reaction, Cu-based catalysts catalyze the reaction of Si particles with alcohols to create a porous structure within Si, followed by carbon deposition via the chemical vapor deposition method. The micro-morphology and -structure of the porous Si materials can be well tuned by adjusting the synthesis conditions. When used as the anode materials for lithium ion batteries, the charge capacity of the obtained porous Si/C materials was 1240 mA h g(-1) at a current density of 50 mA g(-1) after 50 cycles, much higher than that of the commercial graphite. This work provides an economic and scalable approach to the preparation of porous Si/C anode materials from commercial Si powders for lithium ion batteries.

The yolk-shell hollow structure of transition metal oxides has many applications in lithium-ion batteries and catalysis. However, it is still a big challenge to fabricate uniform hollow microspheres with the yolk bishell structure for mixed transition metal oxides and their supported or embedded forms in carbon microspheres with superior lithium storage properties. Here we report a new approach to the synthesis of manganese cobalt iron oxides/carbon (MnxCo1-xFe2O4 (0 ≤ x ≤ 1)) microspheres through carbonization of Mn(2+)Co(2+)Fe(3+)/carbonaceous microspheres in N2, which can be directly applied as high-performance anodes with a long cycle life for lithium storage. Furthermore, uniform hollow microspheres with a MnxCo1-xFe2O4 yolk bishell structure are obtained by annealing the above MnxCo1-xFe2O4/carbon microspheres in air. As demonstrated, these anodes exhibited a high reversible capacity of 498.3 mAh g(-1) even after 500 cycles for Mn0.5Co0.5Fe2O4/carbon microspheres and 774.6 mAh g(-1) over 100 cycles for Mn0.5Co0.5Fe2O4 yolk bishell hollow microspheres at the current density of 200 mA g(-1). The present strategy not only develops a high-performance anode material with long cycle life for lithium-ion batteries but also demonstrates a novel and feasible technique for designed synthesis of transition metal oxides yolk bishell hollow microspheres with various applications.

A series of CeO2-TiO2 and CeO2-TiO2/SiO2 composites were prepared with TiCl4 and Ce (NO3)(3) 6H(2)O as precursors via a facile co-precipitation method. The obtained samples were characterized by various techniques such as X-ray diffraction (XRD), nitrogen adsorption (N-2-BET), Fourier transformation infrared spectrum (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis spectroscopy measurements. The results indicated that TiO2 doped with CeO2 and supported on SiO2 could reduce the crystallite size, inhibit the phase transformation, enhance the thermal stability, and effectively extend the spectral response from UV to visible range. When applied to the phenol photodegradation on a homemade batch reactor with an external cooling jacket, the CeO2-TiO2/SiO2 catalysts exhibited significantly enhanced photodegradation efficiency in comparison with commercial Degussa P25 and CeO2-TiO2. The unique catalytic properties of CeO2-TiO2/SiO2 were ascribed to improved electron-hole pairs separation efficiency and formation of more reactive oxygen species owing to the presence of Ce3+/Ce4+, as well as high dispersion of active component of CeO2-TiO2 as a result of the introduction of SiO2 support. Furthermore, the catalysts can be easily recovered from the reaction solution by centrifugation and reused for four cycles without significant loss of activity. (C) 2015 Elsevier B.V. All rights reserved.

We report a novel catalytic conversion of methanol to C6–C21 hydrocarbons over the bi-functional MFe2O4 (M = Ni, Zn, Mn, Co) catalysts prepared by a solvothermal method. The process consists of two steps: (i) the catalytic reforming of methanol to H2 and CO, and (ii) the subsequent conversion of the syngas to hydrocarbons via Fischer–Tropsch synthesis (FTS). For comparison purposes, two other series of catalysts including MO (M = Ni, Zn, Mn, Co, Fe), and M0.5Co0.5Fe2O4 (M = Ni, Zn, Mn) catalysts were also prepared and tested. All the catalysts were characterized by X-ray diffraction, nitrogen adsorption, transmission electron microscopy, scanning electron microscopy, and H2-temperature programmed reduction. Among these catalysts, ZnFe2O4 exhibited the highest activity with a high methanol conversion of 26% and a high selectivity to C6–C21 hydrocarbons above 94% at 300 °C. Moreover, this ZnFe2O4 catalyst was still stable and reusable after 4 runs under the reaction conditions. This work demonstrates a possibility to directly convert methanol to liquid fuels.

This work demonstrates a new method for fabrication of mixed metal oxide/oxidized graphene (OGP) composites as flexible and binder-free anode materials for Li-ion batteries. The composites containing nickel manganese ferrite (Ni0.5Mn0.5Fe2O4 (NMFO)) nanoparticles grown on an OGP network structure are fabricated by a facile solvothermal method. In the synthesis, Ni(CH3COO)2, Mn(CH3COO)2, and FeCl3 are used as the metal precursors; CH3COONa, HOCH2CH2OH and distilled water as the mixed solvent. The flexible and binder-free electrodes are prepared by coating OGP and NMFO/OGP on polypropylene microporous film via vacuum filtration. The multilayer and porous structure of the NMFO/OGP film generate good contact between the electrode materials and the current collector (OGP film), which is essential for flexible devices. As anticipated, both the free-standing NMFO/OGP film and NMFO/OGP coated on polypropylene microporous film exhibit super-flexible properties without using any binder. The obtained flexible and binder-free electrodes show good electrochemical performance with high lithium storage capacity and excellent cycling stability. This work opens a new way for fabrication of flexible and binder-free anode materials for Li-ion batteries.

A large amount of fine carbon powders (graphite and cokes) are generated as the solid waste in the manufacture of carbon-based materials in industry. How to utilize these abundant powders to generate products with high value still remains a big challenge. Herein, we report the preparation of porous carbon microspheres (PCMs) employing waste non-graphitized needle coke and graphitized needle coke as the fine carbon powder representatives, demonstrating their use as anode materials for lithium-ion batteries. It was found that the graphitized PCMs had a size of 8–30 μm and surface areas between 50 and 120 m2 g−1. When used as the anode materials, their charge capacity at the current density of 50 mA g−1 was comparable to that of the commercial graphite microspheres, but they exhibited higher rate performance.

The oleylamine thermal reduction process was employed to prepare bimetallic copper–silver (CuxAg (0 ≤ x ≤ 50)) nanoparticles, such as Cu, Cu50Ag, Cu20Ag, Cu10Ag, Cu5Ag, CuAg, CuAg2, and Ag, by using Cu(CH3COO)2 and AgNO3 as the precursors. The samples were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The CuxAg hybrid nanostructure showed good particle dispersion, and Cu and Ag metals were well mixed. The catalytic properties of these bimetallic CuxAg nanoparticles as model catalysts for the Rochow reaction were explored. Compared to monometallic Cu and Ag nanoparticles, bimetallic CuxAg nanoparticles resulted in a much higher silicon conversion, which is attributed to the synergistic electronic effect between Cu and Ag metals. For example, the Cu atom was observed to have a lower electron density in the CuxAg bimetallic nanoparticle than that in monometallic Cu nanoparticles, which enhanced the formation of methylchlorosilanes on the silicon surface with chloromethane, demonstrating the significance of the CuxAg bimetallic catalysts in catalytic reactions during organosilane synthesis. The insights gained in this study should be conducive to the design of good Cu-based catalysts for the Rochow reaction.

We report the preparation of porous silicon/carbon microspheres (GPSCMs) by the ball milling and spray drying methods followed by carbonization and chemical vapor deposition processes, in which, the waste fine graphitized needle coke and silicon nanoparticles were employed as the carbon and silicon sources respectively, and sucrose as the binder. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermogravimetric analysis, and Raman spectroscopy. It was found that GPSCMs had spherical sizes of 8–30 μm and surface areas between 20 and 90 m2 g−1. When used as the anode materials for lithium ion batteries, the average charge capacity was 589 mA h g−1 at a current density of 50 mA g−1, much higher than that of the commercial graphite microspheres (GMs). Furthermore, GPSCMs exhibited much better rate performance than the commercial GMs, making them promising for use as the next generation anode materials in lithium ion batteries.

Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsaturated pentahedral Al3+ centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period., Using precious noble elements as single atom metal catalysts is highly desirable and effective. Here the authors show the use of platinum atom catalysts anchored in mesoporous Al2O3 for selective hydrogenation and CO oxidation that have better stability and performance compared to their nanoparticle counterparts.

We report the scalable synthesis of porous Si/C microspheres (PSCMs) by a spray drying process using carbon black (CB) or graphitized carbon black (GCB) nanoparticles as the primary carbon source, Si nanoparticles as the active additive, and sucrose as the binder, followed by a heat treatment at 900 °C. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermogravimetric analysis, and Raman spectroscopy. It was found that the PSCMs have a particle size range of 5–20 μm, and those composed of GCB and 5 wt% Si nanoparticles (named GCBSi5) display improved electrochemical performance. As can be observed, GCBSi5 delivered a reversible capacity of 483 mA h g−1 at the current density of 50 mA g−1 after 100 cycles, which is much higher than that of the commercial graphite microspheres (GMs; 344 mA h g−1). More importantly, GCBSi5 exhibited excellent rate performance, for example, its capacity is around 435 and 380 mA h g−1 at the current densities of 500 and 1000 mA g−1, respectively, which is much higher than those of GMs (200 and 100 mA h g−1). These enhanced electrochemical properties should correlate with its porous structure that can significantly suppress the aggregation and volume expansion/contraction of the Si nanoparticles and speed up Li ion diffusion. In addition, the introduction of GCB and carbon matrix interconnected with hard carbon derived from sucrose can enhance the electronic conductivity. This work demonstrates the feasibility of the large-scale and low-cost production of Si/C anode composites for Li-ion batteries.

Triboelectric nanogenerators (TENGs) provide an effective approach for converting mechanical energy into electricity based on the coupling effect of contact electrification and electrostatic induction. The working principle of TENGs is usually based on one of the four basic modes, namely vertical contact-separation mode, contact-sliding mode, single-electrode (SE) mode, and freestanding-triboelectric-layer (FTL) mode. Here we report a dual-mode rotating TENG (DMR-TENG) with simultaneous outputs from both SE and FTL modes. It is found that the energy output of FTL mode can be promoted by turning on the SE-mode output of the DMR-TENG, which may be due to the change in the amount of charges present in the electrodes. When the DMR-TENG is utilized to concurrently charge two capacitors from the FTL- and SE-mode outputs, respectively, the charging rates of both capacitors increase compared to the case when the DMR-TENG works under either FTL or SE mode. The results indicate that the energy utilization efficiency can be improved for TENGs working under dual modes. Charging a LiFePO4/Li battery and a capacitor from the FTL- and SE-mode outputs of the DMR-TENG has also been demonstrated, evidencing the potential of DMR-TENGs for simultaneous charging multiple energy storage devices of different types.

We report in situ growth of amorphous silicon/carbon (Si/C) layers on graphitized carbon black (GCB) particles in porous microspheres (PMs) for formation of novel GCB@Si/C PMs as high performance anode materials. The preparation included spray drying, KOH activation and chemical vapor deposition at 900 °C, and used methyltrichlorosilane as both the Si and C precursor, which is a cheap byproduct in the organosilane industry. The obtained samples were characterized by X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, transmission electron microscopy, and scanning electron microscopy. Compared with the bare GCB PMs, the GCB@Si/C PMs showed a significantly enhanced electrochemical performance with high lithium storage capacity and excellent cycling stability (the discharge capacity of GCB@Si/C-3 PMs and GCB@Si/C-6 PMs is maintained at 587.2 and 729.7 mA h g−1 after 200 cycles at a current density of 100 mA g−1), because the unique interconnected porous structure within the microspheres could absorb a large portion of Si volume change during Li insertion and extraction reactions, promote the diffusion of Li-ion and electrolyte solution, hinder the cracking or crumbling of the electrode, and additionally, the GCB and amorphous C provide high conductive electron pathway. This work opens a new way for fabrication of Si/C nanocomposites as anode materials for Li-ion batteries.

A general synthetic method based on a solvothermal route for the preparation of multiple transition metal oxide (MTMO) mesoporous nanospheres (ZnaNibMncCodFe2O4, 0 ≤ a, b, c, d ≤ 1, a + b + c + d = 1) with controllable composition and uniform size distribution has been developed. The as-prepared ZnaNibMncCodFe2O4 nanospheres are formed by self-assembly of nanocrystals with the size of 5–10 nm via structure-directing agents and mineralizer coordinating effect as well as optimization of the synthesis conditions. It has been identified that the addition of mineralizer is crucial for the control of the nucleation process when the metallic precursors are reduced; meanwhile the structure-directing agent is key to forming the mesoporous structure. A number of characterization techniques including X-ray diffraction, transmission electron microscopy, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, temperature-programmed reduction, and nitrogen adsorption have been used to characterize the as-prepared mesoporous products. The overall strategy in this work extends the controllable fabrication of high-quality MTMO mesoporous nanospheres with designed components and compositions, rendering these nanospheres with promising potential for various applications (oxygen reduction reaction, magnetic performance, supercapacitor, lithium-ion batteries, and catalysis).

We report a solvothermal synthesis of Ni0.33Mn0.33Co0.33Fe2O4 (NMCFO) nanoparticles anchored on the surface of oxidized carbon nanotubes (OCNT) to form NMCFO/OCNT nanocomposites as advanced anode materials in Li-ion batteries. Ni(CH3COO)2, Mn(CH3COO)2, Co(CH3COO)2, and FeCl3 were employed as the metal precursors and CH3COONa, HOCH2CH2OH and H2O as the mixed solvent in the synthesis. The obtained samples were characterized by X-ray diffraction, thermogravimetric analysis, inductively coupled plasma optical emission spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. It is found that the OCNT provided functional groups on the outer walls to nucleate and anchor NMCFO nanoparticles (5–20 nm), while retaining the inner walls intact with high conductivity. Compared with the bare NMCFO nanoparticles, NMCFO/OCNT composites showed a significantly improved electrochemical performance because OCNT can substantially inhibit the aggregation of NMCFO nanoparticles and buffer the volume change, and moreover, the inner walls of OCNT provide excellent electronic conduction pathways. This work opens an effective way for the fabrication of ferrite-based metal oxide/OCNT hybrids as promising anode materials for Li-ion batteries.

We report the growth of linked silicon/carbon (Si/C) nanospheres on Cu substrate as an integrated anode for Li-ion batteries. The Si/C nanospheres were synthesized by a catalytic chemical vapor deposition (CCVD) on Cu substrate as current collector using methyltrichlorosilane as precursor, a cheap by-product of the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal gravimetry, Raman spectroscopy, nitrogen adsorption, inductively coupled plasma optical emission spectrometry, and X-ray photoelectron spectroscopy. It was found that the linked Si/C nanospheres with a diameter of 400-500 nm contain Si, Cu(x)Si, and Cu nanocrystals, which are highly dispersed in the amorphous carbon nanospheres. A CCVD mechanism was tentatively proposed, in which the evaporated Cu atoms play a critical role to catalytically grown Si nanocrystals embedded within linked Si/C nanospheres. The electrochemical measurement shows that these Si/C nanospheres delivered a capacity of 998.9, 713.1, 320.6, and 817.8 mA h g(-1) at 50, 200, 800, and 50 mA g(-1) respectively after 50 cycles, much higher than that of commercial graphite anode. This is because the amorphous carbon, Cu(x)Si, and Cu in the Si/C nanospheres could buffer the volume change of Si nanocrystals during the Li insertion and extraction reactions, thus hindering the cracking or crumbling of the electrode. Furthermore, the incorporation of conductive Cu(x)Si and Cu nanocrystals and the integration of active electrode materials with Cu substrate may improve the electrical conductivity from the current collector to individual Si active particles, resulting in a remarkably enhanced reversible capacity and cycling stability. The work will be helpful in the fabrication of low cost binder-free Si/C anode materials for Li-ion batteries.

We report in situ growth of mesoporous Mn0.5Co0.5Fe2O4 (MCFO) nanospheres on graphene to form MCFO/graphene nanocomposites by a facile solvothermal method. In the synthesis, Mn(CH3COO)2, Co(CH3COO)2, and FeCl3 were used as the metal precursors and CH3COOK, CH3COOC2H5, and HOCH2CH2OH as the mixed solvent. The obtained MCFO nanospheres (50–200 nm) were composed of small nanoparticles (5–15 nm), and the graphene surface acted as the nucleation sites in growing MCFO nanospheres. Compared with the bare MCFO nanospheres and the MCFO nanospheres physically mixed with graphene, the MCFO/graphene nanocomposite with 2.1 wt % graphene as anode material in Li ion batteries showed a significantly enhanced electrochemical performance with high lithium storage capacity and excellent cycling stability. This is because the introduced graphene can prevent the aggregation of nanospheres and provides a pathway for excellent Li+ ion diffusion and electronic conduction. This work opens a way for facile fabrication of metal oxi...

We report the synthesis and characterization of the mesoporous manganese ferrite (MnFe2O4) microspheres as anode materials for Li-ion batteries. MnFe2O4 microspheres were synthesized by a facile solvothermal method using Mn(CH3COO)2 and FeCl3 as metal precursors in the presence of CH3COOK, CH3COOC2H5, and HOCH2CH2OH. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric, X-ray photoelectron spectroscopy, temperature programmed reduction, and temperature programmed oxidation. The synthesized mesoporous MnFe2O4 microspheres composed of nanoparticles (10–30 nm) were 100–500 nm in diameter and had surface areas between 60.2 and 86.8 m2 g−1, depending on the CH3COOK amounts added in the preparation. After calcined at 600 °C, MnFe2O4 was decomposed to Mn2O3 and Fe2O3 mixture. The mesoporous MnFe2O4 microspheres calcined at 400 °C showed a capacity of 712.2 mA h g−1 at 0.2 C and 552.2 mA h g−1 at 0.8 C after 50 cycles, and an average capacity fading rate of around 0.28%/cycle and 0.48%/cycle, much better than those of the samples without calcination and calcined at 600 °C. The work would be helpful in the fabrication of binary metal oxide anode materials for Li-ion batteries.

We report the preparation of high surface area hedgehog-like CuO microspheres by a wet-chemical method and their application in Li-ion batteries used as anode materials. The samples were characterized by Nitrogen adsorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, temperature-programmed reduction and thermogravimetric analysis. The synthesized hedgehog-like CuO microspheres with a size of 1-3 um possessed a high surface area of 103.5 -157.4 m(2) g(-1) and an average crystal size of 7-9 nm. When used as anode materials, they showed an initial discharge and charge capacity of 1294.6 and 647.6 mAh g(-1), respectively, much higher than the corresponding values of the low surface area CuO microspheres, which are 967.1 and 382.6 mAh g(-1) respectively. After calcination at 300 and 600 degrees C, the morphology of hedgehog-like CuO microspheres was still maintained, and a high capacity of 570-590 mAh g(-1) at 0.1 C was observed after 50 cycles. Meanwhile, the average capacity fading rates for calcined hedgehog-like CuO microspheres were much lower than that of non-calcined and low surface area CuO microspheres, demonstrating that the calcination of CuO microspheres with the high surface area leads to a better cycling performance. This work provides a new method to prepare high surface area CuO materials, which are promising anode materials with high capacity and long cycling life in Li-ion batteries. (C) 2012 Elsevier B.V. All rights reserved.

Despite intensive research into support substrates for the dispersal of nanoparticles and their applications, there has been a lack of general methods to produce metal oxide hollow substrates supporting a wide range of metal and metal oxides. Herein, a synthetic protocol for the preparation of CuO hollow structure-supported MO

We report the comparative investigation on the electrochemical application of mesoporous copper oxide (Cu2O and CuO) microspheres with different surface areas as anode materials in Li-ion batteries. Mesporous Cu2O microspheres with a narrow particle size distribution are synthesized by a hydrothermal method and CuO is obtained by subsequent oxidation of Cu2O. The synthesized mesoporous Cu2O and CuO microspheres possess a surface area of 12.7-65.8 and 5.2-37.6 m(2) g(-1) and an average crystal size of 15.0-20.5 and 10.4-15.9 nm, respectively. The result reveals that the mesoporous Cu2O and CuO microspheres with a higher surface area show a higher capacity and better cyclability than those with a lower surface area. The mesoporous Cu2O and CuO microspheres with a surface area of 65.8 and 37.6 m(2) g(-1) show an initial charge capacity of 430.5 mAh g(-1) and 601.6 mAh g(-1) and deliver a capacity as high as 355.2 mAh g(-1) and 569.8 mAh g(-1) at 0.1 C after 50 cycles, respectively. This is because the highly developed mesoporous structure can enhance the accommodation of lithium ions, shorten the diffusion distance for lithium ions, and increase the absorption of electrolyte. (C) 2012 Elsevier B.V. All rights reserved.

We report the synthesis of Cu@Cu2O core-shell microspheres via a facile template-free solvothermal method. The resulting products were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, transmission electron microscopy, temperature-programmed reduction, and thermogravimetric analysis. It is found that, Cu2O microspheres were firstly formed through the reduction of copper acetate by glutamic acid, and then, the reduction started inside the microspheres due to the higher surface energies of inner Cu2O particles, resulting in the formation of Cu@Cu2O core-shell structure. The content of Cu core in the composite microspheres increased with the reaction time and temperature. The as-prepared Cu@Cu2O core-shell microspheres exhibited a better catalytic performance for dimethyldichlorosilane synthesis than pure Cu2O and Cu, and even superior to the physically mixed Cu and Cu2O microspheres possibly because of the synergistic catalytic effect. These Cu@Cu2O core-shell microspheres will have potential application in organosilicon industry as copper-based catalysts. (C) 2012 Elsevier B.V. All rights reserved.

Porous cubic Cu microparticles were synthesized by a facile solvothermal method using Cu(CH3COO)(2)center dot H2O as the Cu precursor and NaOH in a solution containing ethanol, ethylene glycol, and water. The synthesis conditions were investigated and a growth process of porous cubic Cu microparticles was proposed. The catalytic properties of the porous Cu microparticles as model copper catalysts for Rochow reaction were explored. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction, and nitrogen adsorption. It was found that the morphology and structure of the porous cubic Cu microparticles are highly dependent on the reaction time and temperature as well as on the amount of reactants added. Compared to the commercial Cu microparticles with irregular morphology and dense internal structure, porous cubic Cu microparticles show much higher dimethyldichlorosilane selectivity and Si conversion via Rochow reaction, which are attributed to the enhanced formation of active CuxSi phase and gas transportation in the presence of the pore system within microparticles, demonstrating the significance of the pore structure of the copper catalysts in catalytic reactions of organosilane synthesis.

Mesoporous Cu2O (MP-Cu2O) microspheres were prepared via a facile template-free hydrothermal synthesis in the open system, in which copper acetate was used as the copper precursor and glucose as a reducing agent. The synthesis conditions and catalytic property of MP-Cu2O for dimethyldichlorosilane synthesis via the Rochow reaction were investigated, and the formation mechanism of MP-Cu2O microspheres was proposed. The samples were characterized by nitrogen adsorption, X-ray diffraction, temperature-programmed reduction, thermogravimetric analysis, transmission electron microscopy, and scanning electron microscopy. It was found that the synthesis conditions such as reaction temperature, time, and reactant amount added have a significant effect on the morphology and pore structure of MP-Cu2O microspheres, and MP-Cu2O microspheres were formed through assembly of Cu2O nanoparticles. MP-Cu2O microspheres with a surface area of 65.8 m(2)/g, pore size of 26.7 nm, and a diameter of 400-700 nm were obtained under the optimized condition. As compared to the nonporous Cu2O microspheres, MP-Cu2O microspheres showed a better catalytic performance in dimethyldichlorosilane synthesis due to their developed pore structure and high surface area, which allow larger contact interface among the reaction gas, solid catalyst, and the solid reactant, together with enhanced mass transport. The work would be helpful for developing novel structured copper catalysts for organosilane synthesis and for understanding the catalytic mechanism.

Despite the promising application of porous Si-based anodes in future Li ion batteries, the large-scale synthesis of these materials is still a great challenge. A scalable synthesis of porous Si materials is presented by the Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. Commercial Si microparticles reacted with gas CH3 Cl over various Cu-based catalyst particles to substantially create macropores within the unreacted Si accompanying with carbon deposition to generate porous Si/C composites. Taking advantage of the interconnected porous structure and conductive carbon-coated layer after simple post treatment, these composites as anodes exhibit high reversible capacity and long cycle life. It is expected that by integrating the organosilane synthesis process and controlling reaction conditions, the manufacture of porous Si-based anodes on an industrial scale is highly possible.

We report the preparation and characterization of mesoporous hollow CuO (MPH-CuO) microspheres by thermal decomposition of hollow copper oxalate microspheres synthesized via the reaction of ammonium oxalate and copper chloride without using any template. The sample was characterized by Nitrogen adsorption, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The electrochemical performance of MPH-CuO microspheres as anode materials in Li-ion batteries was evaluated. It was found that the MPH-CuO microspheres possessed an average diameter of 2.5 mu m, a pore size of 17.5 nnn, and a BET surface area of 15.2 m(2)/g. Their shells were composed of CuO nanocrystals with a size, of 17.9 nm. Compared with the dense CuO microspheres, the obtained MPH-CuO shows an enhanced electrochemical performance with a higher capacity of 599.4 mAh/g and a better cyclability (484 mAh/g after 15 cycles) because of its mesoporous hollow structure that provides quick intercalation and large accommodation of lithium ions together with short diffusion distance for lithium ions, suggesting a potential application in Li-ion batteries.

A novel low-cost synthesis route of porous Si materials is developed via ferrite-assisted chemical etching of Si instead of noble metal-assisted chemical etching. The obtained porous Si/C and porous Si/C/ferrite materials used as anodes in Li-ion batteries exhibit good electrochemical performance.

We report the facile preparation of graphitized porous carbon microspheres (GPCMs) by the spray drying technique using carbon black (CB) nanoparticles as the primary carbon resource and sucrose as the binder, followed by graphitization at 2800 °C. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermogravimetric analysis, and Raman spectroscopy. It is found that the GPCMs with a size of 5–20 μm delivered a reversible capacity of 459 mA h g−1 at the current density of 50 mA g−1 after 100 cycles, much higher than that of the commercial graphite microspheres (GMs) (372 mA h g−1). More importantly, GPCMs exhibited excellent rate performances with a capacity of 338 and 300 mA h g−1 at the current densities of 500 and 1000 mA g−1 respectively, superior to those of GMs (200 and 100 mA h g−1). The excellent electrochemical properties of GPCMs originate from its unique structure, which is composed of core–shell nanoparticles with the graphitized carbon core derived from CB nanoparticles and the hard carbon shell generated from sucrose, providing more lithium ion storage sites, higher electronic conductivity, and fast ion diffusion. This work opens a simple way to large-scale production of new carbon anode materials with a low cost and good performance for Li-ion batteries.

We report the preparation of Mn(0.5)Co(0.5)Fe2O4 (MCFO) nanoparticles highly dispersed within porous carbon microspheres as anodes for Li-ion batteries. In situ growth of MCFO nanoparticles (5-20 nm) on the surface of carbon black (CB) and graphitized carbon black (GCB) nanoparticles was conducted via a hydrothermal method to form MCFO-CB and MCFO-GCB composites, respectively, which were employed as building blocks to assemble MCFO-CB and MCFO-GCB porous microspheres (PM) with a size of 5-30 μm by the spray drying technique using sucrose as a binder, and followed by carbonization in N2 (labeled as MCFO-CB-PM and MCFO-GCB-PM, respectively). Compared with the pure MCFO, MCFO-CB, and MCFO-GCB, both MCFO-CB-PM and MCFO-GCB-PM showed a significantly improved electrochemical performance. This is attributed to their unique porous structure, in which, the abundant pores promote the diffusion of Li-ion and electrolyte solution, the microspherical morphology enhances the electrode-electrolyte contact, and the carbon substrates from CB (and GCB) and sucrose substantially prevent the aggregation of MCFO nanoparticles and buffer the volume change. Particularly, MCFO-GCB-PM exhibits the best rate performance and excellent cycling stability because of the high graphitization degree of GCB. This work opens up an effective route for large scale fabrication of metal oxide/carbon porous microspheres as anode materials for potential applications in the new generation of Li-ion batteries.

The metallic Cu flakes prepared by milling metallic Cu powder were controllably oxidized in air at different temperatures to obtain the Cu-based catalysts containing multicomponents of Cu, Cu2O, and CuO. These catalysts are explored in the Rochow reaction using silicon powder and methyl chloride (MeCl) as reactants to produce dimethyldichlorosilane (M2), which is the most important organosilane monomer in the industry. The samples were characterized by X-ray diffraction, temperature-programmed reduction, thermogravimetric analysis, oxidimetry analysis, particle size analysis, transmission electron microscopy, and scanning electron microscopy. Compared to the metallic Cu powder and Cu flakes, the controllably oxidized Cu flakes containing Cu, Cu2O, and CuO species show much higher M2 selectivity and silicon conversion in the Rochow reaction. The enhanced catalytic performance may stem from the larger interfacial contact among the gas MeCl, solid Si particles, and solid Cu-based catalyst flakes, as well as the synergistic effect among the different Cu species. The work would be helpful to the development of novel Cu-based catalysts for organosilane synthesis.