The effect of Ni content on the electrochemical and surface characteristics of Mg90-xTi10Nix (x=50, 55, 60) ternary hydrogen storage electrode alloys

Mg-based ternary Mg90-xTi10Nix (x = 50, 55, 60) electrode alloys of differe nt 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 initia l discharge capacity decreases dramatically. XPS analysis reveals that the outmost surface layer on the Mg-Ti-Ni alloys is a Mg(OH), passive film, in which the content of Mg increases, and the degree of oxidation of Mg become s higher as the cycling goes on. Below the Mg(OH)(2) film is a composite la yer of several oxides including NiO, TiO2 and Mg(OH)(2), This layer is inso luble and compact, and helps to inhibit further corrosion of the fresh allo y surface underneath. In this work, it was also found that with increasing Ni content, the high-rate dischargeability (HRD) and the exchange current d ensity 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. (C) 2001 Elsevier Science B.V. All rights reserved.