Effect of partial substitution of La with Ce, Pr and Nd on the properties of LaNi5-based alloy electrodes

A comparison is made of the properties of LaB5 (B=Ni3.55Co0.75Mn0.4Al0.3), La0.7R0.3B5 (R=Ce, Pr, Nd) and MmB5 (Mm is mischmetal in an atomic ratio of La:Ce:Pr:Nd = 0.7:0.2:0.05:0.05) alloy electrodes. X-ray diffraction results reveal that Ce, Pr, Nd substitute for La and decrease the unit cell volume. Pressure-composition isotherms of the electrode alloys are determined by an electrochemical method. The characteristics of the alloy electrodes, including initial activation, high-rate discharge, cycle life and self-discharge, are examined. It is found that partial replacement of La with Ce, Pr, Nd in the LaNi5-based alloy improves greatly the activation, high-rate discharge and cycle life of the electrode, but increases the self-discharge due to a higher dissociation pressure of the metal hydride.