Electrochemical Hydrogen Storage Kinetics and Microstructure of the Rapidly Quenched Alloy Mg2Ni0.75Zn0.25

Abstract

The Mg2Ni0.75Zn0.25 alloys are prepared from Mg2Ni as master alloy and pure Zinc ingot by remelting process in this work. The microstructures, electrochemical properties and desorption kinetics of the as-cast and melt-spun alloys are investigated. The phase compositions and microstructures of the alloys are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD). The results show that the segregation atoms rich in Zn can inhibit the growth of Mg2Ni grains, especially the nanocrystalline grains formed in Mg2Ni0.75Zn0.25 alloy after melt-spinning process. The rapidly quenched Mg2Ni0.75Zn0.25 alloy exhibits the largest discharge performance (102.1 mAh g−1) and dehydrogenation activation energy (14.68 kJ mol−1). The improvement of the kinetic properties is related to the hydrogen diffusion rate (D) in the alloys and the charge transfer reaction on the surface. The rapidly quenched Mg2Ni0.75Zn0.25 alloy has the largest D, 6.187 × 10−11 cm2 s−1. The doping of Zn aggravates the corrosion of alloy electrodes, which destroys the oxide layer on the alloy surface, provides a channel for the diffusion of hydrogen atoms.