Studies on multi-component rare earth-based hydrogen storage alloys with small amounts of boron

Abstract

Several multi-component Mm-based alloys were prepared by the arc melting method and the electrochemical properties such as capacity, cycling stability and rate capability were examined in 6 N KOH at 30°C. Small amounts of boron in MH alloys noticeably improved the cycling stability of the alloy electrodes regardless of a modest decrease in capacity due to the contraction in unit cell volume. The optimum alloy composition from our experimental results would be of MmNi3.65Co0.62Mn0.36Al0.27B0.1. The initial capacity of this alloy was about 286 mAhg−1 at the 0.2 C rate. The capacity decay after 500 cycles at the 1.0 C rate was 25.7%. After annealing treatments, the alloy showed better cycling stability with a capacity decay of 16.6% after 500 cycles. In addition, the mechanism of hydriding–dehydriding on MH electrodes, and the relationship between the rate capability and the charge-transfer resistance as well as the polarization resistance of alloy electrodes were also discussed.