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）2Ni7phase, La Ni5 phase and（La, Mg）5Ni19phase.Refinement results further show that Nd substitution for La remarkably promotes the formation of La Ni5 phase, while Sm is beneficial for the formation of（La, Mg）5Ni19phase.At discharge current density of 1,875 m A g-1, the highrate 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（I0）, 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 HRD1875 and the corresponding I0/D is found.