Preferential alkaline leaching of amphoteric elements from super-stoichiometric hydrogen storage alloy

Long-lasting charge/discharge cycling (−0.5C/+0.5C) of a super-stoichiometric hydrogen storage alloy with LaNi4.5Co0.5Al0.32Sn0.34Zn0.10 composition has been carried out in a 6 M KOH solution to evaluate the role of selective dissolution of amphoteric elements (Al, Sn and Zn) in electrochemical hydrogenation properties and corrosion behaviour of the hydride electrode. Among alloy constituents, leaching efficiency is the most evident for Sn and Zn additions. Rates of Ni and Co leaching are 2 orders of magnitude lower whereas La is not leached at all. Selective leaching of Al, Sn and Zn is prone to improved material activation and has a minor effect on material passivation and capacity fade. Selective leaching of amphoteric elements as a result of alkaline cycling follows a first-order chemical kinetics law.