Influence of Substituting La with Pr on Electrochemical Characteristics of RE–Mg–Ni-Based A<sub>2</sub>B<sub>7</sub>-Type Alloys Prepared by Melt Spinning

Abstract

The RE–Mg–Ni-based A2B7-type La0.75−xPrxMg0.25Ni3.2 Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys were fabricated by casting and melt spinning. The microstructures and electrochemical characteristics of the as-cast and spun alloys were investigated in detail. The results indicate that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La results in a notable grain refinement of the as-cast alloys without altering the phase structure of the alloys. The discharge capacity of the alloys first rises and then falls with the variation of the Pr content. As Pr content grows from 0 to 0.4, the discharge capacity increases from 389.4 (x = 0) to 392.4 (x = 0.1) and then drops to 383.7 mAh/g (x = 0.4) for the as-cast alloy. And it mounts up from 393.5 (x = 0) to 397.9 (x = 0.1) and then declines to 382.5 mAh/g for the as spun (5 m/s) alloys. Furthermore, the measurements of the electrochemical hydrogen storage kinetics reveal that the high rate discharge ability (HRD), the limiting current density (IL) and the hydrogen diffusion coefficient (D) of the alloys first increases then decreases with the rising amount of Pr substitution.