The effect of substitution of Zr for La on the electrochemical properties of La0.7-xZrxMg0.3Ni2.45Mn0.1Co0.75Al0.2 hydrogen storage electrode alloys

In this paper, the effects of substitution of Zr for La on the structure and electrochemical properties of the La0.7-x ZrxMg0.3Ni2.45Mn0.1Co0.75Al0.2 (x=0, 0.02, 0.04, 0.06, 0.08, 0.1) hydrogen storage alloys have been studied systematically. X-ray powder diffraction (XRD) analysis shows that all the alloys mainly consist of a (La, Mg)Ni-3 phase and a LaNi5 phase. The cell volumes of these two phases decrease with increasing x. Electrochemical studies indicate that the maximum discharge capacity decreases from 364.5 mAh/g (x = 0) to 306.9 mAh/g (x = 0. 1). The high rate dischargeability (HRD) first increases and then decreases with increasing x. Electrochemical impedance spectroscopy (EIS), linear polarization, anodic polarization and potential-step measurements showed that the exchange current density I-0 always decreases, the limiting current density I-L and the hydrogen diffusion coefficient D first increases and then decreases with increasing x from 0 to 0. 1. (c) 2005 Elsevier B.V. All rights reserved.