The effect of Ni content on the electrochemical and surface characteristics of Mg 90− xTi 10Ni x ( x=50, 55, 60) ternary hydrogen storage electrode alloys

Abstract

Mg-based ternary Mg 90− x Ti 10Ni x ( x=50, 55, 60) electrode alloys of different Ni content, were prepared by mechanical alloying (MA) in this work. The main phase of these alloys is amorphous according to the XRD analysis. The electrochemical test indicates that the cycling stability of the electrodes made of these alloys improves with increasing Ni content, while the initial discharge capacity decreases dramatically. XPS analysis reveals that the outmost surface layer on the Mg–Ti–Ni alloys is a Mg(OH) 2 passive film, in which the content of Mg increases, and the degree of oxidation of Mg becomes higher as the cycling goes on. Below the Mg(OH) 2 film is a composite layer of several oxides including NiO, TiO 2 and Mg(OH) 2. This layer is insoluble and compact, and helps to inhibit further corrosion of the fresh alloy surface underneath. In this work, it was also found that with increasing Ni content, the high-rate dischargeability (HRD) and the exchange current density of the ternary Mg–Ti–Ni alloys are significantly increased. Metallic Ni particles generated by reduction from NiO during charging are regarded as the cause for the improved electrochemical activation.