Modification of Ti 0.35Zr 0.65Ni 1.2V 0.6Mn 0.2 alloy powder by electroless nickel coating and its influence on discharge performance

Abstract

The electrochemical performance of an AB 2-type hydrogen storage alloy (Ti 0.35Zr 0.65Ni 1.2V 0.6Mn 0.2) modified by electroless Ni-P and Ni coatings in acid hypophosphite and hydrazine baths, respectively, is investigated. It is found that electrochemical properties of the modified electrodes (i.e., high-rate dischargeability, cycle life, ability to retain discharge capacity after overdischarge) and the electrocatalytic activity for the hydrogen electrode reaction are improved by this surface modification. The high-rate dischargeability of the alloy coated with Ni from the hydrazine bath is better than that coated with NiP from the acid hypophosphite bath, but the activation cycles required for the Ni-coated electrode to reach maximum capacity are four times as many as those required by the electrode coated with NiP. A duplex nickel coating method has therefore been developed. The duplex nickel-coated alloy (i.e., alloy first coated with NiP and then coated with Ni) retains the characteristics of better high-rate dischargeability but requires fewer activation cycles in comparison with the Ni-coated alloy.