An electrochemical investigation of Mg1−xAlxNi (0 ≤ x ≤ 0.6) hydrogen storage alloys

Abstract

Mg2−xAlxNi (0≤x≤0.6) series alloys have been successfully synthesized by interdiffusing Mg, Ni and Al powders together. The effects of partial substitution of Al for Mg on the structure and electrochemical performance have been investigated. XRD result shows that a new compound, Mg3AlNi2, with cubic structure, S. G. Fd3m, emerges. PCT measurement shows that Mg1.5Al0.5Ni alloy has lower hydrogen capacity, but it can absorb hydrogen at lower temperature. The electrochemical capacity and cycle life of alloy electrodes increase markedly with increasing amount of the new compound in alloys. The highest electrochemical capacity of Mg1.5Al0.5Ni reaches 226mAhg−1 without any treatment due to its excellent discharge capability. The results of CV and EIS measurements show that the alloys containing the new compound, Mg3AlNi2, present excellent electrochemical performance, and the rate-determining process changes from charge-transfer process of the parent alloy, Mg2Ni, to a hydrogen diffusion-controlled process for the Mg2−xAlxNi (0.3≤x≤0.5) alloys. These results suggest that cubic Mg3AlNi2 alloy maybe a promising hydrogen storage material for future use in hydrogen storage systems and Ni–MH batteries.