Effect of Ni Substitution for Co on the Electrochemical Properties of La0.75Mg0.25Ni2.74+xCo0.4-xMn0.1Al0.3 (x=0-0.4) Hydrogen Storage Alloys Synthesized by Chemical Co-precipitation plus Reduction Method

The feasibility of substituting nickel for cobalt in La-Mg-Ni-based hydrogen storage alloys to reduce material costs and improve electrochemical properties is investigated. The series of alloys with the chemical formula La(0.75)Mg(0.25)Ni(2.7+x)Co(0.4-x)Mn(0.01)Al(0.)3 (x = 0-0.4) that reflects the gradual substitution of Ni for Co are prepared by chemical co-precipitation plus reduction method. The detailed synthesis process, structure, morphology, electrochemical performance, and kinetic properties of the resulting alloy electrodes are discussed in terms of the variation in substitution amount of Ni for Co. Results reveal that the hydrogen storage alloy substituted with x = 0.1 exhibits the best overall electrochemical performance among all investigated samples, whereas the complete substitution of Ni for Co has no significant effect on electrochemical performance. Based on these results, a mechanism underlying the effect of substituting Ni for Co on the electrochemical performance of the resulting alloy is discussed in detail and effectively verified by conducting three electrochemical kinetic experiments. Complete substitution of Ni for Co is found to be suitable for reducing material costs and improving the overall electrochemical performances of La-Mg-Ni-based hydrogen storage alloys. (C) 2013 The Electrochemical Society. All rights reserved.