Investigation on the structure and electrochemical properties of AB3-type La-Mg-Ni-Co-based hydrogen storage composites

The La0.7Mg0.3Ni2.75Co0.75 and Ti0.17Zr0.08V0.35Cr0.1Ni0.3 alloys were prepared by vacuum magnetic levitation melting and the La-Mg-Ni-Co-based composites containing Ti0.17Zr0.08V0.35Cr0.1Ni0.3 with different weight ratios (5, 10, 15 and 20%) were successfully synthesized by ball milling method. The XRD analyses showed that all these composites mainly consisted of the (La, Mg)Ni3 phase with the rhombohedral PuNi3-type structure and the LaNi5 phase with the hexagonal CaCu5-type structure, the cell volumes of the (La, Mg)Ni3 phase increased with the increasing Ti0.17Zr0.08V0.35Cr0.1Ni0.3 weight ratio, while the cell volumes of LaNi5 phase decreased. The electrochemical measurements showed that the maximum discharge capacity of the composites decreased, and the cycling life improved distinctly with increasing Ti0.17Zr0.08V0.35Cr0.1Ni0.3 weight ratio, which can be ascribed to the improved anti-corrosion performance of composite electrode in KOH solution. However, the electrochemical impedance spectroscopy (EIS) and anodic polarization (AP) measurements showed that the kinetics of composite electrodes was retarded with the increase of Ti0.17Zr0.08V0.35Cr0.1Ni0.3 amount. These results suggest that the formation of composite with Ti0.17Zr0.08V0.35Cr0.1Ni0.3 alloy is a promising strategy for improving the cyclic life of AB3-type La-Mg-Ni-Co-based alloy.