Electrochemical hydrogen storage of ball-milled Mg-rich Mg–Nd alloy with Ni powders

The Mg-rich Mg–Nd alloy was synthesized by salt-cover-melting. It is found that the Nd5Mg41 phase with tetragonal structure exists as the main phase in the as-cast Mg-rich Mg–Nd alloy. The microstructure and electrochemical hydrogen storage of the composites prepared by ball-milling the Mg-rich Mg–Nd alloy with Ni powders are investigated. The result reveals that the addition of a larger amount of metallic Ni during the ball-milling process is beneficial to the formation of highly dispersed Ni nanocrystalline on the amorphous Mg-rich Mg–Nd alloy matrix of the composites. The composite, prepared by ball-milling the Mg-rich Mg–Nd alloy with 200 wt.% Ni, is demonstrated to have the discharge capacity of about 953 mAh/g in the first cycle. The appearance of stronger hydrogen adsorption peaks in cyclic voltammograms is very sensitive to the surface Ni-rich dispersion of the composites. The rate-determining step for the electrochemical reaction is transformed from a mixed process of the hydrogen diffusion and surface charge-transfer to a single process of the surface charge-transfer as the Ni amount in the Mg-rich Mg–Nd alloy–Ni composites is increased.