Influence of Substituting La with Zr on Electrochemical Characteristics of As-Spun RE–Mg–Ni-Based A<sub>2</sub>B<sub>7</sub>-Type Alloys

Abstract

In order to ameriolate the electrochemical hydrogen storage performances of La–Mg–Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were prepared by melt spinning. The influences of substithting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated. The structure characterized by XRD and TEM displays that the as-spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun Zr-free alloy displays an entire nanocrystalline structure, while an like amorphous structure is detected in the as-spun alloy substituted by Zr, implying that the substitution of Zr for La facilitates the amorphous formation. The substitution of Zr for La markedly enhances the electrochemical cycle stability of the alloys, whereas the impact generated by such substitution on the high rate discharge ability (HRD) of the alloys is different with the variation of the spinning rate. The HRD of the as-spun (5 m/s) alloys yields the largest value with the change of Zr content, but that of the as-spun (20 m/s) alloys always declines with the growing amount of Zr substitution.