Effect of Temperature on Electrode Kinetic Parameters for Hydrogen and Oxygen Evolution Reactions on Nickel Electrodes in Alkaline Solutions

The electrode kinetic parameters for hydrogen and oxygen evolution were determined at temperatures of 80 ~ 150 ~ 208 ~ and 264 ~ on nickel electrodes in 50 weight per cent KOH solutions. Improvements in the exchange current density with increasing temperature were more significant for the oxygen evolution reaction than for the hydrogen evolution reaction. A favorable change in the Tafel slope for the oxygen evolution reaction occurs between 150 ~ and 264 ~ which corresponds to an increase in the transfer coefficient from 0.67 to 3.3. This result supports the concept hat a change in the reaction mechanism occurs for the oxygen electrode reaction ear the Neel temperature of nickel oxide. At the higher experimental temperatures, the Tafel slope for the hydrogen evolution reaction changes from 2RT/3F at low overpotentials to about 2RT/F at high overpotentials suggesting a slow electrochemical desorp-tion mechanism. The present study indicates that significant reductions in cell voltage for water electrolysis can be obtained by higher operating tem-