Modification of Ti0.35Zr0.65Ni1.2V0.6Mn0.2 alloy powder by electroless nickel coating and its influence on discharge performance

The electrochemical performance of an AB(2)-type hydrogen storage alloy (Ti0.35Zr0.65Ni1.2V0.6Mn0.2) 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.