An investigation on electrochemical hydrogen storage performances of the as-cast and -annealed La0.8−xSmxMg0.2Ni3.35Al0.1Si0.05 (x = 0–0.4) alloys

Abstract

The as-cast and -annealed La–Mg–Ni-based A2B7-type La0.8−xSmxMg0.2Ni3.35Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were prepared, and the influences of the partial substitution of Sm for La on the structure and electrochemical performances of the alloys were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical measurements. The results indicate that all the experimental alloys mainly consist of two phases, (La, Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. The substitution of Sm for La gives rise to an obvious change in the electrochemical performances of the alloys. The discharge capacity of the as-cast and -annealed alloys first increases and then decreases with the growing of Sm content, whereas the cycle stability of the as-cast and -annealed alloys always increases with the rising of Sm content. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS), Tafel polarization curves and potential-step measurements all indicate that the electrochemical kinetic properties of the alloy electrodes first increase then decrease with the rising amount of Sm substitution.