Effects of substituting La with M (M=Sm, Nd, Pr) on electrochemical hydrogen storage characteristics of A2B7-type electrode alloys

The partial substitution of M (M=Sm, Nd, Pr) for La was performed in order to ameliorate the electrochemical hydrogen storage performance of RE-Mg-Ni-based A2B7-type electrode alloys. The La0.8-xMxMg0.2Ni3.35Al0.1Si0.05 (M=Sm, Nd, Pr; x=0-0.4) electrode alloys were fabricated by casting and annealing and their microstructures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The major phases (La, Mg)2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCu5-type structure make up the basic microstructure of the experimental alloys. The discharge capacities of the as-cast and annealed alloys all gain their maximum values with the M (M=Sm, Nd, Pr) content varying. The electrochemical cycle stability of the as-cast and annealed alloys clearly rises with the M (M=Sm, Nd, Pr) content growing. Furthermore, the electrochemical kinetics of the alloys, including the high rate discharge ability, charge transfer rate, limiting current density and hydrogen diffusion coefficient, all present a increase trend at first and then decrease with the rising of M (M=Sm, Nd, Pr) content.