Phase structure and electrochemical performances of Co-free La–Mg–Ni-based alloys with Nd/Sm partial substitution for La

In this paper, the Co-free hydrogen storage alloys with the nominal compositions of La0.75R0.05Mg0.20Ni3.40Al0.10 (R = La, Nd and Sm) were prepared by induction melting, and then the phase structure and electrochemical properties of these alloys were comparatively investigated. It is found that the alloys mainly consist of (La, Mg)2Ni7 phase, LaNi5 phase and (La, Mg)5Ni19 phase. Refinement results further show that Nd substitution for La remarkably promotes the formation of LaNi5 phase, while Sm is beneficial for the formation of (La, Mg)5Ni19 phase. At discharge current density of 1,875 mA·g−1, the high-rate dischargeability (HRD) of alloy electrodes increases by 13.9 % and 6.5 % with La substituted by Nd and Sm, respectively. The electrochemical kinetic measurements reveal that the exchange current density (I 0), charge transfer resistance (R) and hydrogen diffusion coefficient (D) for the alloy electrode are all facilitated with Nd and Sm partial substitution for La. Subsequently, a linear correlation between the HRD 1875 and the corresponding I 0/D is found.