Crystallographic and Electrochemical Characteristics ofLa 0.7 Mg 0.3 Ni 4.5– x (Al 0.5 Mo 0.5 ) x ( x = 0–0.8) Hydrogen Storage Alloys

The structure, hydrogen storage property, and electrochemical characteristics of the La 0.7 Mg 0.3 Ni 4.5– x (Al 0.5 Mo 0.5 ) x ( x = 0, 0.2, 0.4, 0.6, 0.8) hydrogen storage alloys have been investigated systematically. The X‐ray powder diffraction and Rietveld analysis results reveal that all the alloys mainly consist of the La(La, Mg) 2 Ni 9 phase and the LaNi 5 phase. The electrochemical measurements show that the maximum discharge capacity increases first from 246.3 ( x = 0) to 345.4 mAh/g ( x = 0.6) and then decreases to 317.6 mAh/g ( x = 0.8), which is consistent with the variation of the hydrogen storage capacity indicated by the P‐C isotherms. For the discharge current density of 1200 mA/g, the high‐rate dischargeability of the alloy electrodes increases linearly from 47.2 % ( x = 0) to 73.8 % ( x = 0.8). Moreover, according to the linear polarization curves, the exchange current density of the alloy electrodes also increases monotonously with increasing x . The hydrogen diffusion coefficient increases with increasing Al and Mo content, and thus increases the low‐temperature dischargeability of the alloy electrodes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)