Electrochemical characteristics of nanocrystalline and amorphous Mg–Y–Ni-based Mg2Ni-type alloys prepared by mechanical milling

Abstract

Abstract Nanocrystalline and amorphous Mg2Ni-type Mg20–x Y x Ni10 (x = 0, 1, 2, 3 and 4) electrode alloys were prepared by mechanical milling. The structures of the as-cast and milled alloys were determined by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The electrochemical hydrogen storage performances of the alloys were tested by an automatic galvanostatic system. The electrochemical impedance spectra, Tafel polarization curves and potential-step curves were plotted by an electrochemical workstation. The results indicate that a nanocrystalline structure can successfully be obtained through mechanical milling. The substitution of Y for Mg facilitates glass forming and leads to an obvious change in the phase composition. The substitution of Y for Mg dramatically improves the cycle stability of the as-milled alloys, while the mechanical milling more or less impairs the cycle stability of the alloys. The discharge capacity of the alloys first augments and then declines with increasing Y content and milling time. Furthermore, the high rate discharge ability, charge transfer rate, limiting current density and diffusion coefficient of hydrogen atomic all decrease with Y content and milling time increasing.