Effect of chemical etching on protium absorbing properties and electrochemical characteristics of LaNi₅ alloys

When hydrogen storage alloy is used as a negative electrode of nickel-metal hydride batteries, protium absorbing properties at a negative electrode is different from those at a gas phase because of the formation of oxide layers and a nickel-rich layer on the surface of the alloy due to charge and discharge. This paper investigates the effect of surface chemical etching on protium absorbing properties and electrochemical characteristics of LaNi₅ alloys. Dilute HCl solution under 1% was used as etchants for the formation of a nickel-rich layer which works as a protection surface of the alloy against the KOH electrolyte. Protium absorbing properties of annealed LaNi₅ samples which were etched shortly with 0.2N HCl or 0.02N HCl were better protium storage capacity than those of unetched annealed LaNi₅ samples. Electrochemical characteristics of annealed LaNi₅ samples which were etched for 60min with 0.02N HCl were better cycle stability than those of unetched annealed LaNi₅ samples.