Impacts of melt spinning and Mn replacement on electrochemical hydrogen storage performances of nanocrystalline and amorphous Mg2Ni-type alloys

The Mg2Ni-type alloys with a nanocrystalline and amorphous structure have been confirmed possessing superior electrochemical hydrogen storage kinetics. The melt-spinning technique is used to preparing the nanocrystalline and amorphous Mg2Ni-type alloys with the nominal compositions of Mg20Ni10-xMnx (x = 0, 1, 2, 3, 4). The impacts of the melt spinning and the replacement of Ni by Mn on the structures and the electrochemical performances of the alloys are investigated systematically. The analysis of the structures by XRD and HRTEM reveals that the replacement of Ni by Mn facilitates the glass formation in the Mg2Ni-type alloy, and the amorphization degree of the as-spun alloys increases with the growing of the spinning rate. Furthermore, the replacement renders the formation of secondary phases MnNi and Mg instead of altering the Mg2Ni major phase in the alloys. The measurement of the electrochemical characteristics by an automatic galvanostatic system indicates that the discharge capacity and cycle stability of the alloys dramatically grow with the rising of the spinning rate and the amount of Mn replacement, with which the high rate discharge ability (BIRD) of the alloys first augments and then falls.