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

In order to improve the electrochemical performance of the La–Mg–Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Pr and melt spinning technology was used for preparing La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures and electrochemical performance of the as-cast and spun alloys were investigated in detail. The results obtained by XRD, SEM and TEM 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 results of the electrochemical measurement indicate that the discharge capacity of the alloys first increases and then decreases with variation of the Pr content. The cycle stability of the alloy monotonically rises with increasing Pr content. When the Pr content rises 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. Discharge capacity increases 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. The capacity remaining after 100 cycles increases from 65.32 to 79.36% for the as-cast alloy, and from 73.97 to 93.08% for the as-spun (20 m/s) alloy.