An investigation on the structural and electrochemical properties of La_0.7Mg_0.3(Ni_0.85Co_0.15)_x (x=3.15-3.80) hydrogen storage electrode alloys

In this paper, the structural and electrochemical properties of the La_0.7Mg_0.3(Ni_0.85Co_0.15)_x (x=3.15, 3.30, 3.50, 3.65, 3.80) hydrogen storage electrode alloys have been studied systematically. From the XRD analyses, each alloy of this series is composed of the LaNi₃ phase and the LaNi₅ phase, and the phase abundance of each phase varies with the degree of non-stoichiometry x and determines the hydrogen absorption capacity of the alloy. The electrochemical studies show that as x increases the maximum discharge capacity first increases from 365.7 mAh/g (x=3.15) to 398.4 mAh/g (x=3.50) and then decreases to 328.5 mAh/g (x=3.80). Moreover, as x increases from 3.15 to 3.80, the high rate dischargeability (HRD), the exchange current density (I₀), the limiting current density (I_L) and the diffusion coefficient (D), of the alloy electrodes all increase first and then decrease.