STUDIES ON MULTICOMPONENT RARE EARTH-BASED HYDROGEN STORAGE ALLOYS WITH SMALL AMOUNTS OF BORON

Several multi-component him-based alloys were prepared by the are melt ing method and the electrochemical properties such as capacity, cyclin g stability and rate capability were examined in 6 N KOH at 30 degrees C. Small amounts of boron in MPI alloys noticeably improved the cycli ng stability of the alloy electrodes regardless of a modest decrease i n capacity due to the contraction in unit cell volume. The optimum all oy composition from our experimental results would be of MmNi(3.65)Co( 0.62)Mn(0.36)Al(0.27)B(0.1). The initial capacity of this alloy was ab out 286 mA h g(-1) at the 0.2 C rate. The capacity decay after 500 cyc les 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 c harge-transfer resistance as well as the polarization resistance of al loy electrodes were also discussed. (C) 1998 Elsevier Science S.A. All rights reserved.