[en] A shuttle effect caused by soluble intermediates is one of the most crucial issues in lithium sulfur batteries, which results in a short cycle life and low coulombic efficiency. Recently, binary metal sulfides as electrode materials have been used for miscellaneous application accounting for their larger redox reaction sites and higher electrical conductivity. Herein, a novel urchin-like NiCo₂S₄ was synthesized via two steps of hydrothermal process and then firstly used as a conductive and polar host for sulfur in lithium sulfur batteries. The obtained NiCo₂S₄/S composite demonstrates a capacity of 1028 mAh g⁻¹ for the first discharge and maintains 421 mAh g⁻¹ after 100 cycles at 0.1 C. Furthermore, the composite still shows a remarkable cycling stability at a higher rate, a low capacity fade rate of 0.18% per cycle can be achieved and a reversible capacity of 329 mAh g⁻¹ can be obtained after 300 cycles at 1 C. This excellent performance results from a weakened polysulfide shuttle caused by a strong affinity between NiCo₂S₄ and polysulfides.

[en] Nickel sulfides are desirable electrode materials for supercapacitors, while low electronic conductivity and poor cyclic stability restrict their wide applications. Herein, Ni₂CoS₄/expanded graphite (Ni₂CoS₄/EG) composite was prepared in mixed solvents of ethylene glycol and H₂O via a rapid and energy-saving microwave heating method. Scanning transmission electron microscopy image shows that Ni₂CoS₄ particles are ultrafine with an average diameter of 2 nm and uniformly distributed on expanded graphite. The specific capacitance of the Ni₂CoS₄/EG composite can reach up to 2056.8 F g⁻¹ at 5 A g⁻¹ as compared to 1574.4 F g⁻¹ of Ni₃S₄, 229.1 F g⁻¹ of CoS and 1516.6 F g⁻¹ of Ni₂CoS₄; and even at higher current density of 30 A g⁻¹, the specific capacitance can still demonstrates 1923.3 F g⁻¹, thus 92.5% of rate capability can be achieved as the current density increases from 5 to 30 A g⁻¹. Moreover, it exhibits an excellent stability of 94.4% after cycling at current density of 30 A g⁻¹ for 2000 cycles. The composite delivers high initial capacitance, excellent rate capability, and fantastic stability. Furthermore, the fabricated AC//Ni₂CoS₄/EG asymmetric supercapacitor also exhibits a high specific capacitance of 120.3 F g⁻¹ at 0.5 A g⁻¹, an superior cycle life (91% at 5 A g⁻¹ for 5000 cycles), and an extremely high energy density of 52 Wh kg⁻¹ at 477 W kg⁻¹. This work offers a new insight to synthesize ultrafine bimetallic sulfides, and the superior high performances of the Ni₂CoS₄/EG composite can provide practical applications in supercapacitors.

[en] Transition metal selenides, a new type of electrode material for electrochemical capacitors, have attracted much attention because of their superior capacitive performance, notable electrical conductivity, and abundant reserves. Facile and efficient microwave heating followed by a solvothermal method was used to synthesize the (Ni_0.85Se)₃(Co_0.85Se)/reduced graphene oxide (rGO) composite. Firstly, it can be observed that (Ni_0.85Se)₃(Co_0.85Se)/rGO presents a three-dimensional porous microstructure consisting of stacked nanorods. The as-synthesized (Ni_0.85Se)₃(Co_0.85Se)/rGO has an excellent specific capacitance of 2009 F g^-1 at a current density of 2 A g^-1, an ultrahigh rate performance of 83% with an increment in current density from 2 A g^-1 to 30 A g^-1, together with an outstanding long-cycle performance of 79.7% capacitance retention after 5000 cycles at 30 A g^-1. Furthermore, the assembled (Ni_0.85Se)₃(Co_0.85Se)/rGO||activated carbon (AC) asymmetric supercapacitor achieves a high energy density of 38 W h kg^-1 at a power density of 388 W kg^-1. After 5000 cycles at a current density of 10 A g^-1, the capacitance retention is 80.8%, which promotes the potential application of (Ni_0.85Se)₃(Co_0.85Se)/rGO for high-performance supercapacitors. (authors)

[en] Ni(OH)₂/AC/CNT composite has been prepared via a green rapid microwave assisted method in an ethylene glycol medium. Scanning electron microscopy images show that Ni(OH)₂ nanoparticles, activated carbon spheres and nanotubes constructed a three-dimensional (3-D) connected network, which lead to a high specific capacitance 1038 F g⁻¹ at current density of 1 A g⁻¹. Based on Ni(OH)₂/AC/CNT composite as positive electrode material and activated carbon as negative electrode material, an asymmetric supercapacitor of AC//Ni(OH)₂/AC/CNT was fabricated. The unit supercapacitor demonstrates excellent electrochemical performances using non-woven fabric as separator and 6 M KOH as electrolyte within 1.6 V operation window. The maximum specific capacitance of 82.1 F g⁻¹ is achieved at 0.5 A g⁻¹ and the energy density can reach up to 32.3 Wh kg⁻¹ at power density of 504.8 W kg⁻¹. Furthermore, 83.5% capacitance retention is obtained after 1000 charge-discharge cycles. These results indicate that the AC//Ni(OH)₂/AC/CNT supercapacitor is promising to be applied in a practical device for energy storage devices.

[en] A 500 h life-test of direct methanol fuel cell (DMFC) was conducted in a single cell. X-ray diffraction (XRD) and transmission electron microscopy (TEM) images showed that after life-test, the particle size of electrocatalysts increased both in anode and cathode, and the degree is higher in cathode. Electrochemical areas (ECAs) of anode and cathode catalyst were evaluated by CO-stripping and hydrogen-desorption test, respectively. It was found that the ECA loss is higher than the specific surface area (SSA) loss (determined by XRD) that merely due to the sintering of the electrocatalyst particles. Energy dispersive X-ray analysis (EDX) revealed a crossover of ruthenium from the anode side to the cathode side in the cell

[en] Carbon supported PtSn alloy and PtSnO _x particles with nominal Pt:Sn ratios of 3:1 were prepared by a modified polyol method. High resolution transmission electron microscopy (HRTEM) and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of PtSn particles. The particles are predominantly single nanocrystals with diameters in the order of 2.0-3.0 nm. According to the XRD results, the lattice constant of Pt in the PtSn alloy is dilated due to Sn atoms penetrating into the Pt crystalline lattice. While for PtSnO _x nanoparticles, the lattice constant of Pt only changed a little. HRTEM micrograph of PtSnO _x clearly shows that the change of the spacing of Pt (1 1 1) plane is neglectable, meanwhile, SnO₂ nanoparticles, characterized with the nominal 0.264 nm spacing of SnO₂ (1 0 1) plane, were found in the vicinity of Pt particles. In contrast, the HRTEM micrograph of PtSn alloy shows that the spacing of Pt (1 1 1) plane extends to 0.234 nm from the original 0.226 nm. High resolution energy dispersive X-ray spectroscopy (HR-EDS) analyses show that all investigated particles in the two PtSn catalysts represent uniform Pt/Sn compositions very close to the nominal one. Cyclic voltammograms (CV) in sulfuric acid show that the hydrogen ad/desorption was inhibited on the surface of PtSn alloy compared to that on the surface of the PtSnO _x catalyst. PtSnO _x catalyst showed higher catalytic activity for ethanol electro-oxidation than PtSn alloy from the results of chronoamperometry (CA) analysis and the performance of direct ethanol fuel cells (DEFCs). It is deduced that the unchanged lattice parameter of Pt in the PtSnO _x catalyst is favorable to ethanol adsorption and meanwhile, tin oxide in the vicinity of Pt nanoparticles could offer oxygen species conveniently to remove the CO-like species of ethanolic residues to free Pt active sites

[en] In this work, high-surface supported PtRu/C were prepared with Ru(NO)(NO₃)₃ and [Pt(H₂NCH₂CH₂NH₂)₂]Cl₂ as the precursors and hydrogen as a reducing agent. XRD and TEM analyses showed that the PtRu/C catalysts with different loadings possessed small and homogeneous metal particles. Even at high metal loading (40 wt.% Pt, 20 wt.% Ru) the mean metal particle size is less than 4 nm. Meanwhile, the calculated Pt crystalline lattice parameter and Pt (2 2 0) peak position indicated that the geometric structure of Pt was modified by Ru atoms. Among the prepared catalysts, the lattice parameter of 40-20 wt.% PtRu/C contract most. Cyclic voltammetry (CV), chronoamperometry (CA), CO stripping and single direct methanol fuel cell tests jointly suggested that the 40-20 wt.% PtRu/C catalyst has the highest electrochemical activity for methanol oxidation