Electrochemical hydrogen storage properties of La0.7Mg0.3Ni3.5-Ti0.17Zr0.08V0.35Cr0.1Ni0.3 composites

For further improving the electrochemical properties of nonstoichiometric AB(3)-type La0.7Mg0.3Ni3.5 alloy as negative electrode of Ni-MH battery, its related composites La0.7Mg0.3Ni3.5-xwt% Ti0.17Zr0.08V0.35Cr0.1Ni0.3 (x = 5, 10, 25, 40) are prepared by ball milling method. It is found that all these composites are mainly composed of (LaMg)Ni-3 and LaNi5 phases according to XRD patterns. When x <= 25, the V-based solid solution BCC phase and C14 Laves phase in Ti0.17Zr0.08V0.35Cr0.1Ni0.3 alloy are not detectable. As x further increases to 40wt%, however, these two phases appear in XRD pattern. Electrochemical studies show that the maximum discharge capacity of these electrodes decreases slightly from 348.5 mAh/g (x = 5) to 335.2 mAh/g (x = 40), while the cyclic capacity retention rate of composite electrodes is significantly improved from 29.7% (x = 5) to 63.0% (x = 40) after 70 charge-discharge cycles. This improvement of cyclic life can be ascribed to the enhanced anti-corrosion performance of composite electrode in alkaline solution. Moreover, the electrochemical kinetics properties, including the charge-transfer resistance R-ct, the polarization resistance R-p, the exchange cur-rent density I-0, the limiting current density I-L and the hydrogen diffusion coefficient D, of the composite electrodes were retarded first with x increasing from 5 to 25 and then improved when x reaches to 40. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.