Structures and electrochemical hydrogen storage characteristics of La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0-0.4) alloys prepared by melt spinning

A2B7-type electrode alloys with nominal compositions of La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt-spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage characteristics of the as-cast and spun alloys were measured. The obtained results show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La leads to an obvious increase of the (La, Mg)Ni3 phase and a decrease of the LaNi5 phase in the alloys. The discharge capacity of the alloys first increases and then decreases with variety of the spinning rate except the (x = 0.4) alloy. The cycle stability of the alloy monotonously rises with increasing spinning rate. When spinning rate rises from 0 (as-cast was defined as spinning rate of 0 m/s) to 20 m/s, the discharge capacity increases from 389.4 (0 m/s) to 393.5 (5 m/s) and then drops to 374 mAh/g (20 m/s) for the (x = 0) alloy, and it mounts up from 392.4 (0 m/s) to 397.9 (5 m/s), after that declines to 383.6 mAh/g (20 m/s) for the (x = 0.1) alloy. The capacity retaining rate after 100 cycles increases from 65.32% to 73.97% for the (x = 0) alloy, and from 73.65% to 86.91% for the (x = 0.1) alloy.