Effect of MWCNTs and lithium modified MWCNTs on electrochemical hydrogen storage properties of Co0.9Cu0.1Si alloy

Mechanical alloying technique was used to prepare the Co0.9Cu0.1Si alloy. Composite materials of Co0.9Cu0.1Si 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 Co0.9Cu0.1Si. 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 Co0.9Cu0.1Si alloy. The electro-catalytic function of MWCNTs, the reduction of particle size and the raise of specific surface area for Co0.9Cu0.1Si 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 Co0.9Cu0.1Si 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.