The effects of partial substitution of Cr for Ni on the electrochemical properties of Mg1.75Al0.25Ni1−xCrx (0 ≤ x ≤ 0.3) electrode alloys

In this paper, the substitution of different amounts of Cr for Ni in the hydrogen storage electrode alloy of Mg1.75Al0.25Ni has been carried out to form quaternary Mg1.75Al0.25Ni1−xCrx (0 ≤ x ≤ 0.3) alloys by means of solid diffusion method (DM). The XRD profiles exhibited that the quaternary alloys still kept the same main phase of Mg3AlNi2 (S.G. Fd3m) as that of ternary Mg1.75Al0.25Ni alloy. The electrochemical studies found that Cr substituted quaternary alloy reached its maximum discharge capacity (165 mAh g−1) after 2 cycles, which was larger than that of the Mg1.75Al0.25Ni alloy (154 mAh g−1). Among these quaternary alloys, the Mg1.75Al0.25Ni0.9Cr0.1 electrode alloy was found possessing the highest cycling capacity retention rate. Cyclic voltammetry (CV) results and anodic polarization curves demonstrated that appropriate content (x lower than 0.1) of Cr effectively improved the reaction activity of electrode and inhibited the cycling capacity degradation to some degree. Electrochemical impedance spectroscopy (EIS) analyses indicated that the increase of Cr content would raise the polarization resistance Rp on the particle surface of these quaternary alloys.