MIXING EFFECT OF METAL-OXIDES ON NEGATIVE ELECTRODE-REACTIONS IN THE NICKEL-HYDRIDE BATTERY

Negative electrodes for use in nickel-hydride batteries were prepared from MmNi3.6Mn0.4Al0.3Co0.7 (Mm = misch metal with the composition of 24.87% La, 52.56% Ce, 5.57% Pr, 16.86% Nd, and 0.14% Sm) alloy being mixed with RuO2 or Co3O4 powder. Then the hydrogen evolution reactions at the electrodes were investigated by measuring the potential decay immediately after the interruption of an applied cathodic current. The reactions were found to proceed by the Volmer-Tafel mechanism. The total overvoltage (eta) was divided into two components (eta1 and eta2) corresponding to the Tafel and Volmer reactions. The exchange current densities of the elementary reactions, i0V and i0T, were then evaluated by extrapolating the Tafel lines for eta1 and eta2. The Volmer reaction is much more accelerated by surface modification with RuO2 or Co3O4 powder than the Tafel reaction, which results in the enrichment of adsorbed hydrogen, leading to higher charging efficiency.