Effect of Al and W substitution for Ni on the microstructure and electrochemical properties of hydrogen storage alloys

The microstructure and electrochemical properties of La 1.3 CaMg 0.7 Ni 9 - x ( Al 0.5 W 0.5 ) 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 LaNi 5 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 ) Ni 3 phase and the LaNi 5 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.