Electrochemical hydrogen storage behaviors of the nanocrystalline and amorphous Nd-Cu-added Mg2Ni-type alloy electrodes applied to Ni-MH battery

In order to ameliorate the electrochemical characteristics of Mg2Ni-type alloy, the elements Cu and Nd are added in the alloy. The nanocrystalline and amorphous Mg2Ni-type alloys with the composition of (Mg24Ni10Cu2)(100-x) Nd (x) (x = 0, 5, 10, 15, 20) are prepared by melt spinning technology. The effects of Nd content and spinning rate on structures and electrochemical performances of the alloys are investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal that the as-spun Nd-free alloy displays an entirely nanocrystalline structure, whereas the as-spun Nd-15 alloy, differing from Nd-0 alloy, exhibits nanocrystals embedded in an amorphous matrix. This suggests that the addition of Nd facilitates the amorphous formation ability of the alloys. The electrochemical measurement indicates that both adding Nd and melt spinning significantly improve the electrochemical performances of the alloys, involving the discharge potential characteristics, discharge capacity, cycle stability, and the high rate dischargeability (HRD). The Nd addition and melt spinning enhance the diffusion ability of hydrogen atoms in the alloy, but both of them impair the charge-transfer ability on the surface of the alloy electrode, which gives rise to the HRD values first mounting up and then going down with the growing of the Nd content and the spinning rate.