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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 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.

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.

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.

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.

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.

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.

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 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 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.

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.

We report a facile chemical vapor deposition (CVD) method to grow silicon/carbon ( Si / C ) microspheres on commercial graphite microsphere (GMs) surface to prepare Si / C / GMs composite anode materials for Li -ion batteries. The CVD synthesis is conducted at 900°C using methyltrichlorosilane ( CH 3 SiCl 3) as both the Si and C precursor, which is a cheap byproduct in organosilane industry. The samples are characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and X-ray photoelectron spectroscopy. It is found that the obtained Si / C / GMs composites are composed of Si nanocrystals, amorphous carbon and GMs. The CVD time significantly influences the morphology and electrochemical performance of the Si / C / GMs composite materials. The Si / C / GMs composite materials prepared at CVD condition of 900°C for 4 h possess improved electrochemical properties, showing a discharge capacity of 821.4 mAh g−1 at a rate of 50 mA g−1, and a good cycling performance (i.e., a reversible capacity of 565.2 mAh g−1 is retained after 50 cycles). The enhanced electrochemical performance is attributed to the formation of Si / C microsphere network among GMs, which increases the electronic conductivity and is able to buffer the large volume changes of Si during lithium ion insertion/extraction.

Flower-like CuO microspheres synthesized by a facile hydrothermal method were found to be an effective catalyst for the Rochow reaction with a higher dimethyldichlorosilane selectivity and Si conversion because of the enhanced formation of an active CuxSi phase and mass transport.