Abstract

The corrosion rates of LaNi5 and LaNi3.55Co0.75Mn0.4Al0.3 hydride electrodes, soaked in alkaline electrolyte and under charge-discharge cycling, were investigated by linear polarization, Tafel polarization and a new method based on the difference between the charge and discharge capacities. The corrosion-inhibition by Ni in LaNi5 and the influence of zincate ions on the corrosion rate of LaNi5 and LaNi3.55Co0.75Mn0.4Al0.3 were also studied. The results showed that the hydride electrode exhibits different corrosion behaviour when immersed in alkaline electrolyte and during charge-discharge cycles. The corrosion rate of LaNi5 was lower than that of LaNi3.55Co0.75Mn0.4Al0.3 when simply soaked in 6 M KOH solution, but higher during the charge-discharge cycles. The corrosion-inhibition afforded by Zn(OH)42- ions on LaNi3.55Co0.75Mn0.4Al0.3 is small under quiescent conditions, but increases upon charge-discharge operation; such corrosion-inhibition improves the cycle-life of the hydride electrode.