Effect of rare earth elements on electrochemical properties of La-Mg-Ni-based hydrogen storage alloys

La0.60R0.20Mg0.20(NiCoMnAl)(3.5) (R = La, Ce, Pr, Nd) alloys were prepared by inductive melting. Variations in phase structure and electrochemical properties due to partial replacement of La by Ce, Pr and Nd, were investigated. The alloys consist mainly of LaNi5 phase, La2Ni7 phase and LaNi3 phase as explored by XRD and SEM. The maximum discharge capacity decreases with Ce, Pr and Nd substitution for La. However, the cycling stability is improved by substituting Pr and Nd at La sites, capacity retention rate at the 100th cycle increases by 13.4% for the Nd-substituted alloy. The electrochemical kinetics measurements show that Ce and Pr substitution improves kinetics and thus ameliorates the high rate dischargeability (HRD) and low temperature dischargeability. The HRD at 1200 mA g(-1) increases from 22.1% to 61.3% and the capacity at 233 K mounts up from 90 mAh g-1 to 220 mAh g(-1) for the Ce-substituted alloy. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.