Oxygen Reduction on Oxide-Free Platinum in 85%Orthophosphoric Acid: Temperature and Impurity Dependence

Oxygen electrode kinetics in 85% orthophosphoric acid have been studied as a function of temperature and impurity level in the electrolyte. It is shown that the mechanism of reaction is the same as that in N perchloric acid, and that rate constants and Tafel slopes are dependent on impurity adsorption. Hydrogen peroxide is not a significant reaction product, at least at high temperatures. The activation energy of the reaction at the reversible potential was determined to be