Oxygen reduction on a ruthenium electrode in acid electrolytes

The kinetics and mechanism of O2 reduction on an Ru electrode in acid electrolytes have been measured by using a disc—ring method. The reaction proceeds through a “parallel” mechanism with the exchange of approximately four electrons. It shows a pronounced dependence on the oxidation state of the Ru surface. A catalytic decomposition of H2O2 does not occur on the surface obtained at potentials E > 0.0 V. Tafel slopes, some rate constants and reaction orders for O2 and H2O2 reduction have been determined. Calculated rate constant for a direct reduction of O2 (k1) is higher than k2, the reduction with the H2O2 intermediate. The experimental value of k3, the H2O2 reduction, is lower than k1 and k2 at E > 0.05 V. The Tafel slope for O2 reduction with the value higher than 120 mV has been obtained