Influence of Oxygen Content on Microstructure and Electrochemical Properties of V2-xTi0.5Cr0.5NiOx (x=0∼0.35) Hydrogen Storage Alloys

To improve the charge-discharge cycle stability of V-based hydrogen storage alloys, the different contents of oxygen (0) element were introduced into the V2Ti0.5Cr0.5Ni alloy, and the structures and electrochemical properties of the V2Ti0.5Cr0.5NiOx (x=0 similar to 0.35) alloys were investigated. The structural investigations show that the alloys with lower 0 content mainly consist of a V-based solid solution phase with a bcc structure and a TiNi-based secondary phase, while a new phase Ti4Ni2O is observed for the alloys with higher 0 content. With increasing of 0 content, the maximum discharge capacity for the V2-xTi0.5Cr0.5NiOx (x=0 similar to 0.35) alloy electrodes decreases from 366.8 mAh/g (x=0) to 225.3 mAh/g (x=0.35), while the cycle stability of the alloy electrodes first increases from 69.9% (x=0) to 83.7% (x=0.2) and then decreases to 76.9% (x=0.35). Moreover, the high rate discharge ability, the exchange current density and the hydrogen diffusion coefficient of the alloys first increase and then decrease with increasing of O content.