Effects of partial substitution by Fe and Co for Ni in the Mg1.75Al0.25 Ni electrode alloy on their electrochemical performances

In this paper, Co and Fe were selected as the partial substitution elements for Ni to form Mg1.75Al0.25Ni0.9X0.1 quaternary electrode alloys prepared by means of solid diffusion method (DM) on the basis of the ternary Mg1.75Al0.25Ni alloy. The XRD patterns exhibited that quaternary alloys still possessed the main phase of Mg3AlNi2 as that of the ternary Mg1.75Al0.25Ni alloy when introducing the substitution elements Co or Fe. The electrochemical studies found that Fe- or Co-substituted quaternary alloy possessed larger discharge capacity and higher cycling stability than the Mg1.75Al0.25Ni ternary alloy. Cyclic voltammetry (CV) tests demonstrated that the additional Fe and Co could improve the electrocatalytic oxidation activity on the surface and also the discharge capacity of the Mg1.75Al0.25Ni electrode alloy. Anodic polarization curves indicated that the additional Fe and Co led to potentials shifting toward position direction and decrease of the corrosion current. Electrochemical impedance spectroscopy (EIS) revealed that the exchange current density decreases considerably with the augmentation of the cycle number.