Mechanical alloying technique was used to prepare the Co 0.9 Cu 0.1 Si alloy. Composite materials of Co 0.9 Cu 0.1 Si doping with different amounts of multi-walled carbon nanotubes (MWCNTs) or lithium modified MWCNTs (Li-MWCNTs) were obtained via ball-milling to improve the hydrogen storage performance of Co 0.9 Cu 0.1 Si. XRD , SEM and TEM were used to analysis the structural properties of the samples. A three-electrode battery system was carried out to test the electrochemical properties . After the addition of MWCNTs, the composites showed higher discharge capacity, stronger HRD, better cyclic stability and lower charge-transfer resistance than the original Co 0.9 Cu 0.1 Si alloy. The electro-catalytic function of MWCNTs, the reduction of particle size and the raise of specific surface area for Co 0.9 Cu 0.1 Si alloy may provide larger electrochemically accessible area and rapid channel for hydrogen transportation , which are important to enhance the electrochemical performance of the alloy. Moreover, a further improvement was achieved after the addition of Li-MWCNTs, illustrating that the MWCNTs and lithium species had synergistic effects in improving the discharge capacity and reaction kinetics of the Co 0.9 Cu 0.1 Si alloy electrode. As the weight ratio of the alloy and Li-MWCNTs was 15:1, the optimal discharge capacity of 624.4 mAh/g and the highest capacity retention of 67.5% were achieved.
The current hydrogen storage alloys used for Ni-MH battery negative electrode are difficult to guarantee excellent performance in terms of discharge capacity and cycle stability. Co 0.9 Cu 0.1 Si alloy has been widely investigated as a negative electrode material for nickel hydrogen battery, but its capacity and cycle stability need to be improved for commercial applications. In this work, Co 0.9 Cu 0.1 Si alloy was prepared by mechanical alloying. Molybdenum carbide (Mo 2 C) was loaded on multi-walled carbon nanotubes (MWCNTs) by in-situ carburizing . In order to improve the electrochemical hydrogen storage performance of Co 0.9 Cu 0.1 Si alloy, 5 wt% MWCNTs, Mo 2 C and molybdenum carbide modified multi-walled carbon nanotubes (Mo 2 C@MWCNTs) were added to Co 0.9 Cu 0.1 Si alloy via mechanical alloying method. The structure and morphology of the composites were characterized by XRD and SEM. The discharge capacity, cyclic stability and high rate discharge performance of the composites were tested, the electrochemical performance of the composites was investigated by three-electrode battery system. The composite materials have better discharge capacity, cycle stability and electrochemical performance compared with the pristine alloy. The Co 0.9 Cu 0.1 Si alloy doped with 5 wt% Mo 2 C@MWCNTs-2 has the best electrochemical hydrogen storage performance among all the composite materials. Its optimal discharge capacity is 609.9 mAh/g and its maximum capacity retention rate is 64.7 %. The enhancement of the electrochemical hydrogen storage performances of the composites are due to the high conductivity and high specific surface area of MWCNTs and the high catalytic activity of Mo 2 C. The synergistic effect of MWCNTs and Mo 2 C can improve the electrochemical hydrogen storage performances of the composites.
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