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To develop a long cycle life and good rate capability electrode, 3D hierarchical porous α-Fe2O3 nanosheets are fabricated on copper foil and directly used as binder-free anode for lithium-ion batteries. This electrode exhibits a high reversible capacity and excellent rate capability. A reversible capacity up to 877.7 mAh g−1 is maintained at 2 C (2.01 A g−1) after 1000 cycles, and even when the current is increased to 20 C (20.1 A g−1), a capacity of 433 mA h g−1 is retained. The unique porous 3D hierarchical nanostructure improves electronic-ionic transport, mitigates the internal mechanical stress induced by the volume variations of the electrode upon cycling, and forms a 3D conductive network during cycling. No addition of any electrochemically inactive conductive agents or polymer binders is required. Therefore, binder-free electrodes further avoid the uneven distribution of conductive carbon on the current collector due to physical mixing and the addition of an insulator (binder), which has benefits leading to outstanding electrochemical performance. [ABSTRACT FROM AUTHOR]

Cu-doped Li4Ti5O12-TiO2 nanosheets were synthesized by a facile, cheap, and environmentally friendly solution-based method. These nanostructures were investigated as an anode material for lithium-ion batteries. Cu doping was found to enhance the electron conductivity of the materials, and the amount of Cu doped controlled the crystal structure and content of TiO2. In addition, the samples, which benefit from multiphases and doping, exhibited much improved capacity, cycle performance, and high rate capability over Cu-free Li4Ti5O12-TiO2. The discharge capacity of the 0.05 Cu-doped sample was 190 mAh g−1 at 1C, and even 144 mAh g−1 was obtained at 30C after 100 cycles. Moreover, after 500 cycles at 30C, the discharge capacity remained at approximately 130 mAh g−1. The excellent electrochemical performance of the cell demonstrated that Cu-doping was able to adjust and control the Li4Ti5O12-TiO2 system appropriately. [ABSTRACT FROM AUTHOR]

Two types of porous cobalt manganese oxide nanowires (MnCo2O4 and CoMn2O4) with different structures have been successfully synthesized by thermal decomposition of organometallic compounds for the first time. Nitrilotriacetic acid (NA) was used as a chelating agent to coordinate Co(II) and Mn(II) ions in various molar ratios, in a hydrothermal condition. The microstructure of as-synthesized cobalt manganese oxides, composed of numerous nanoparticles, completely retains the 1D network structure of the Co -- Mn -- NA coordination precursors without structure collapse. Electrochemical properties of the cobalt manganese oxide materials have been tested for supercapacitors at room temperature. Both the MnCo2O4 and CoMn2O4 electrodes display the outstanding capacitive behaviors and superior electrochemical properties. The CoMn2O4 nanowire shows excellent capacitance and desirable rate performance (2108 F g-1 at 1 A g-1 and 1191 F g-1 at 20 A g-1) compared to that of the MnCo2O4 nanowire (1342 F g-1 at 1 A g-1 and 988 F g-1 at 20 A g-1). Electrochemical impedance spectra (EIS) results also reconfirm that the CoMn2O4 nanowires display more facile electrolyte diffusion and higher capacitor response frequency than MnCo2O4 nanowires. This can be ascribed to the facile electrolyte/OH- ion penetration and better Faradaic utilization of the electroactive surface sites that generated by the smaller particle size and higher surface area. [ABSTRACT FROM AUTHOR]

An efficient core-shell Co@C catalyst is synthesized through a solvothermal and subsequent annealing process. The as-synthesized Co@C consists of an 11 nm Co core and a 3 nm amorphous carbon shell. Nitrogen sorption isothermals show that Co@C has a surface area of 112.6 m2 g-1 and a typical pore size of 4.8 nm. The catalytic effects of core-shell Co@C, which can significantly improve the dehydrogenation performance of MgH2, are systematically investigated. With increasing amounts of Co@C (0, 3, 5, 10, 15 wt%), the dehydrogenation temperature of MgH2 decreased. Its dehydrogenation kinetics are also improved, especially for the MgH2-10%Co@C sample, which starts to release hydrogen at 168 °C. In fact, about 6.00 wt% hydrogen is released during its decomposition, and the activation energy of MgH2-10%Co@C is determined to be 84.5 kJ mol-1, 46.2% less than that of pure MgH2. Mechanism analysis indicates that upon increasing the Co@C content, the decomposition of MgH2 gradually occurs along lower-dimensional nucleation and growth. Moreover, the excellent thermal conductivity of the carbon shell in Co@C also contributes to the enhanced dehydrogenation performance of MgH2. [ABSTRACT FROM AUTHOR]

Bimetallic NiCo functional graphene (NiCo/rGO) was synthesized by a facile one-pot method. During the coreduction process, the as-synthesized ultrafine NiCo nanoparticles (NPs), with a typical size of 4-6 nm, were uniformly anchored onto the surface of reduced graphene oxide (rGO). The NiCo bimetal-supported graphene was found to be more efficient than their single metals. Synergetic catalysis of NiCo NPs and rGO was confirmed, which can significantly improve the hydrogen-storage properties of MgH2. The apparent activation energy (Ea) of the MgH2-NiCo/rGO sample decreases to 105 kJ mol-1, which is 40.7% lower than that of pure MgH2. More importantly, the as-prepared MgH2-NiCo/rGO sample can absorb 5.5 and 6.1 wt% hydrogen within 100 and 350 s, respectively, at 300 °C under 0.9 MPa H2 pressure. Further cyclic kinetics investigation indicates that MgH2-NiCo/rGO nanocomposites have excellent cycle stability. [ABSTRACT FROM AUTHOR]

Size-controlled Ag0.04@Co0.48@Ni0.48 core-shell nanoparticles (NPs) were synthesized by employing graphene (rGO) with different reduction degrees as supports. The number of CO and CO functional groups on the surface of rGO might play a major role in controlling the particle size. The strong steric-hindrance effect of CO resulted in the growth of large particles, whereas CO contributed to the formation of small particles. The particle size of Ag0.04@Co0.48@Ni0.48 NPs supported on rGO with different reduction degrees decreased as the number of CO functional groups decreased. The decrease in the particle size probably led to the increase in the catalytic activity towards the hydrolysis of ammonia borane (AB). The enhanced catalytic activity largely stemmed from the increasing active sites on the surface of catalysts owing to the decreasing particle size. [ABSTRACT FROM AUTHOR]

Triple-layered Ag@Co@Ni core-shell nanoparticles (NPs) containing a silver core, a cobalt inner shell, and a nickel outer shell were formed by an in situ chemical reduction method. The thickness of the double shells varied with different cobalt and nickel contents. Ag0.04@Co0.48@Ni0.48 showed the most distinct core-shell structure. Compared with its bimetallic core-shell counterparts, this catalyst showed higher catalytic activity for the hydrolysis of NH3BH3 (AB). The synergetic interaction between Co and Ni in Ag0.04@Co0.48@Ni0.48 NPs may play a critical role in the enhanced catalytic activity. Furthermore, cobalt-nickel double shells surrounding the silver core in the special triple-layered core-shell structure provided increasing amounts of active sites on the surface to facilitate the catalytic reaction. These promising catalysts may lead to applications for AB in the field of fuel cells. [ABSTRACT FROM AUTHOR]