Growth and Properties of Oxide Films on Platinum II. pH Dependence in Alkaline Solutions

The kinetics of growth of the oxide film on platinum has been studied in alkaline solutions as a function of pH. The experimental data confirm the existence of steady states in the current and thickness. Diagnostic criteria for the dependence of the steady state current and thickness on applied potential and pH are derived from the PDM, in which the point defects in the barrier layer are postulated to be cation vacancies, cation interstitials, and oxygen vacancies. The steady state thickness is then predicted to vary linearly with the applied potential and pH. These predictions are in good agreement with the experimental findings. The kinetic order of the barrier layer dissolution reaction with respect to the hydrogen ion concentration in the alkaline solutions is found to be negative, which indicates that the platinate anion might be formed during film dissolution.