Influences of substituting Ni with M (M=Cu, Co, Mn) on gaseous and electrochemical hydrogen storage kinetics of Mg20Ni10 alloys

In this work, a comprehensive comparison regarding the impacts of M (M=Cu, Co, Mn) substitution for Ni on the structures and the hydrogen storage kinetics of the nanocrystalline and amorphous Mg20Ni10-x M (x) (M=Cu, Co, Mn; x=0-4) alloys prepared by melt spinning has been carried out. The analysis of XRD and TEM reveals that the as-spun (M=None, Cu) alloys display an entire nanocrystalline structure, whereas the as-spun (M=Co, Mn) alloys hold a mixed structure of nanocrystalline and amorphous structure when M content x=4, indicating that the substitution of M (M=Co, Mn) for Ni facilitates the glass formation in the Mg2Ni-type alloy. Besides, all the as-spun alloys have a major phase of Mg2Ni but M (M=Co, Mn) substitution brings on the formation of some secondary phases, MgCo2 and Mg phases for M=Co as well as MnNi and Mg phases for M=Mn. Based upon the measurements of the automatic Sieverts apparatus and the automatic galvanostatic system, the impacts engendered by M (M=Cu, Co, Mn) substitution on the gaseous and electrochemical hydrogen storage kinetics of the alloys appear to be evident. The gaseous hydriding kinetics of the alloys first rises and then declines with the growing of M (M=Cu, Co, Mn) content. Particularly, the M (M= Mn) substitution results in a sharp drop in the hydriding kinetics when x=4. The M (M=Cu, Co, Mn) substitution ameliorates the dehydriding kinetics dramatically in the order (M=Co)>(M=Mn)>(M=Cu). The electrochemical kinetics of the alloys visibly grows with M content rising for (M=Cu, Co), while it first increases and then declines for (M=Mn).