Improved Hydrogen Storage Kinetics of Nanocrystalline and Amorphous Mg-Nd-Ni-Cu-based Mg2Ni-type Alloys by Adding Nd

In order to improve the gaseous and electrochemical hydrogen storage kinetics of the Mg2Ni-type alloy, the elements Cu and Nd were 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) were prepared by melt spinning technology. The effects of Nd content on the structures and hydrogen storage kinetics of the alloys were investigated. The characterization by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) reveals that all the as-cast alloys hold multiphase structures, containing Mg2Ni-type major phase as well as some secondary phases Mg6Ni, Nd5Mg41, and NdNi, whose amounts clearly grow with increasing Nd content. Furthermore, the as-spun Nd-free alloy displays an entire nanocrystalline structure, whereas the as-spun Nd-added alloys hold a mixed structure of nanocrystalline and amorphous structure and the amorphization degree of the alloys visibly increases with the rising of the Nd content, suggesting that the addition of Nd facilitates the glass forming in the Mg2Ni-type alloy. The measurement of the hydrogen storage kinetics indicates that the addition of Nd significantly improves the gaseous and electrochemical hydrogen storage kinetics of the alloys. The addition of Nd enhances the diffusion ability of hydrogen atoms in the alloy, but it impairs the charge-transfer reaction on the surface of the alloy electrode, which makes the high rate discharge ability (HRD) of the alloy electrode first mount up and then go down with the growing of Nd content.