Crystallographic and Electrochemical Characteristics ofLa0.7Mg0.3Ni4.5–x(Al0.5Mo0.5)x (x = 0–0.8) Hydrogen Storage Alloys

The structure, hydrogen storage property, and electrochemical characteristics of the La0.7Mg0.3Ni4.5–x(Al0.5Mo0.5)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)2Ni9 phase and the LaNi5 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)