Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3.5 − x(Al0.5Mo0.5)x (x = 0–0.8) hydrogen storage alloys

Abstract The crystal structure, hydrogen storage property and electrochemical characteristics of the La 0.7 Mg 0.3 Ni 3.5 −  x (Al 0.5 Mo 0.5 ) x ( x  = 0–0.8) alloys have been investigated systematically. It can be found that with X-ray powder diffraction and Rietveld analysis the alloys are of multiphase alloy and consisted of impurity LaNi phase and two main crystallographic phases, namely the La(La, Mg) 2 Ni 9 phase and the LaNi 5 phase, and the lattice parameter and the cell volume of both the La(La, Mg) 2 Ni 9 phase and the LaNi 5 phase increases with increasing Al and Mo content in the alloys. The P – C isotherms curves indicate that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x , and the equilibrium pressure decreases with increasing x . The electrochemical measurements show that the maximum discharge capacity first increases from 354.2 ( x  = 0) to 397.6 mAh g −1 ( x  = 0.6) and then decreases to 370.4 mAh g −1 ( x  = 0.8). The high-rate dischargeability of the alloy electrode increases lineally from 55.7% ( x  = 0) to 73.8% ( x  = 0.8) at the discharge current density of 1200 mA g −1 . Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x . The hydrogen diffusion coefficient in the alloy bulk increases with increasing Al and Mo content and thus enhances the low-temperature dischargeability of the alloy electrode.