Effect of Al and W substitution for Ni on the microstructure and electrochemical properties of La1.3CaMg0.7Ni9-x (Al0.5W0.5)x hydrogen storage alloys

The microstructure and electrochemical properties of La1.3CaMg0.7Ni9-x (Al0.5W0.5)(x) (x = 0, 0.3, 0.6, 0.9) hydrogen storage alloys have been studied systematically. XRD and SEM analyses show that the alloys are mainly composed of the(La, Mg)Ni-3 phase and the LaNi5 phase, but the Al and W substitution for Ni results the disappearance of the (La, Mg)(2)Ni-7 phase and the segregation of W pure metal phase. The cell volumes of the (La, Mg)Ni3 phase and the LaNi5 phase increase by adding the content of Al. With increasing x, the maximum discharge capacity of the alloy electrodes decreases from 380 (x = 0.0) to 317.6 mA h/g (x = 0.9). However, cyclic stability is noticeable improved from 72.2% (x = 0.0) to 85.2% (x = 0.9) up to 100 cycles. The HRD and exchange current density I-0 of the alloy electrodes decrease first and then increase. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.