Corrosion effect on the electrochemical properties of LaNi3.55Mn0.4Al0.3Co0.75 and LaNi3.55Mn0.4Al0.3Fe0.75 negative electrodes used in Ni–MH batteries

The thermodynamic parameters, electrochemical capacity, equilibrium potential and the equilibrium pressure, of LaNi3.55Mn0.4Al0.3Co0.75 and LaNi3.55Mn0.4Al0.3Fe0.75 alloys have been evaluated from the electrochemical isotherms (C/30 and OCV methods) and CV technique. A comparative study has been done between the parameter values deduced from the electrochemical methods and the solid–gas method. The parameter values deduced from the electrochemical methods are influenced by the electrochemical corrosion of the alloys in aqueous KOH electrolyte. The corrosion behaviour of the LaNi3.55Mn0.4Al0.3Co0.75 and LaNi3.55Mn0.4Al0.3Fe0.75 electrodes after activation was investigated using the method of the potentiodynamic polarization. The variation of current and potential corrosion values with the state of charge (SOC) show that the substitution of cobalt by iron accentuates the corrosion process. The high-rate dischargeability (HRD) of the LaNi3.55Mn0.4Al0.3Co0.75 and LaNi3.55Mn0.4Al0.3Fe0.75 alloys was examined. By increasing the discharge current the (HRD) decrease linearly for both the alloys and for the LaNi3.55Mn0.4Al0.3Fe0.75 compound is greater then for the LaNi3.55Mn0.4Al0.3Co0.75 one.