The Oxygen-Evolution Reaction at Gold Anodes

The oxygen‐evolution reaction at gold anodes was studied in 0.1 M H 2 SO 4 at 25 °C. The factors affecting the accuracy of overpotential measurements and a new cell design for improved accuracy with a Luggin‐Haber capillary are described. Current distribution in the cell, limitations imposed by competing reactions and by the IR drop included in the measurement, overpotential‐time curves at constant current density, and the accuracy with which Tafel's equation is obeyed are presented. The current density range for accurate measurements was found to be 3 × 10 − 5 to 10 − 2 amp cm − 2 . Overpotential measurements taken with decreasing and increasing currents were reproducible to ±1 mv, and deviations from the Tafel line were within this variation. At constant current density the gold anodes oxidized to hydrated Au 2 O 3 following the linear law, and the current density dependence of the oxidation rate indicated a blister mechanism.