Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3 − x(Al0.5Mo0.5)x (x = 0–0.4) hydrogen storage alloys

Abstract The effect of partial substitution of Al and Mo for Ni on the structure and electrochemical properties of the La 0.7 Mg 0.3 Ni 3 −  x (Al 0.5 Mo 0.5 ) x ( x  = 0–0.4) hydrogen storage alloys have been investigated systematically. The result of X-ray powder diffraction (XRD) and Rietveld analysis show that all the alloys consist of the La(La, Mg) 2 Ni 9 phase and the LaNi 5 phase. Meanwhile, the lattice parameter and the cell volume of both the La(La, Mg) 2 Ni 9 phase and the LaNi 5 phase increase with increasing Al and Mo contents in the alloys. The pressure composition isotherms curves indicate that the hydrogen storage capacity first increases and then decreases with increasing x . The electrochemical measurements show that the maximum discharge capacity of the alloy electrodes first increases from 343.3 ( x  = 0) to 377.6 mAh/g ( x  = 0.3) and then decreases to 350.4 mAh/g ( x  = 0.4). Moreover, the high rate dischargeability (HRD) and the exchange current density of the alloy electrodes decrease first and then increases with the increase of x in the alloys. The hydrogen diffusion coefficient increases with increasing Al and Mo content and thus increases the low temperature dischargeability (LTD) of the alloy electrodes.