Enhanced electrochemical characteristics of as-spun nanocrystalline and amorphous Mg 2Ni-type alloy electrodes

Abstract

The nanocrystalline and amorphous Mg 2Ni-type electrode alloys with nominal compositions of Mg 2Ni 1− x Mn x ( x = 0, 0.1, 0.2, 0.3, 0.4) are synthesized by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are obtained. The structures of the as-spun alloy ribbons are characterized by XRD, SEM and TEM. The electrochemical characteristics as well as the electrochemical impedance spectrums (EIS) of the as-spun alloy electrodes are measured. The hydrogen diffusion coefficients ( D) in the alloys were obtained by virtue of potential-step method. The results show that the as-spun ( x = 0) alloy holds a typical nanocrystalline structure, whereas the as-spun ( x = 0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni evidently intensifies the glass forming ability of the Mg 2Ni-type alloy. The substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving the discharge capacity and the electrochemical cycle stability. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) and the potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with rising the amount of Mn substitution.