Electrochemical Hydrogen Storage Kinetics of La0.75-x ZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0-0.2) Alloys Prepared by Melt Spinning

The RE–Mg–Ni-based A2B7-type La0.75–xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were fabricated by casting and melt spinning. The influences of the melt spinning on the structures and the electrochemical hydrogen storage kinetics of the alloys were investigated. The structure characterized by XRD, SEM and HRTEM and the results reveal that the as-cast and 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, but a like amorphous structure is detected in the as-spun alloy substituted by Zr, suggesting that the substitution of Zr for La facilitate the amorphous formation. The melt spinning engenders different impact on the high rate discharge ability (HRD) of the Zr-free and Zr substitution alloys. As the spinning rate is enhanced from 0 (As-cast is defined as the spinning arte of 0 m/s) to 20 m/s, the HRD of the Zr-free (x = 0) alloy grows from 94.28% (0 m/s) to 95.15% (10 m/s) and then declines to 89.23% (20 m/s). And that of the Zr substitution (x = 0.15) alloy monotonously falls from 90.45% to 80.07%. Furthermore, the electrochemical impedance spectrum (EIS), the Tafel polarization curves and the potential-step measurements all indicate that the electrochemical kinetics first increases then decreases for the Zr-free alloy, but all of them always decline for the alloy substituted by Zr with the growing of spinning rate.