The effect of partial substitution of Ti with Zr, Cr or V in the Mg35Ti10Ni55 electrode alloy on its electrochemical performance

In this paper, Zr. Cr and V were selected as the partial substitution elements for Ti to form Mg35Ti5M5Ni55 quaternary alloys prepared by means of mechanical alloying on the basis of the ternary Mg35Ti10Ni55 electrode alloy previously studied by the authors. It is found that all the three quaternary alloys possess an amorphous main phase and exhibit improved cycling stability than the original ternary Mg35Ti10Ni55. The Zr-substituted alloy has also a higher discharge capacity. X-ray photoelectron spectroscopy (XPS) surface analysis reveals that on the surface of each alloy a multi-component oxide composite film is formed, which is more compact and corrosion resistant than the Mg(OH), film and the (TiO2)(x)(NiO)(y)(Mg(OH)(2))(z) composite films reported previously. Auger electron spectroscopy (AES) analysis shows that the substituting elements tend to reduce the thickness of the passivation films. The thickness of composite oxide film on the alloys is in the following order: Mg35Ti10Ni55 > Mg35Ti5V5Ni55 > Mg35Ti5Zr5Ni55 > Mg35Ti5Cr5Ni55. The result agrees well with that of the polarization resistances (R-p) values obtained from the electrochemical impedance spectroscopy (EIS) Nyquist diagrams. It demonstrates that the thicker the passivation film is. the higher the Rp is and the more difficultly the charge transfer reaction proceeds. Anodic polarization curves indicate that the addition of Cr and Zr decreases effectively the corrosion current. However, the corrosion of the electrode alloys in the electrolyte is still high and proceeds constantly as the corrosion current remains almost constant during further cycles. (C) 2002 Elsevier Science Ltd. All rights reserved.