KINETICS AND MECHANISM OF THE ELECTROCHEMICAL REDUCTION OF MOLECULAR-OXYGEN ON PLATINUM IN KOH - INFLUENCE OF PREFERRED CRYSTALLOGRAPHIC ORIENTATION

The oxygen electroreduction reaction has been studied at both preferre d oriented and conventional polycrystalline platinum rotating disc ele ctrodes in x M KOH (0.05 less-than-or-equal-to x less-than-or-equal-to 3.0) aqueous solutions under oxygen saturation at 25-degrees-C. At lo w current densities, Tafel lines with slope -0.060 V decade-1 have bee n obtained at all platinum electrodes. At high current densities, high er Tafel slopes ranging from -0.18 to -0.40 V decade-1 have been obser ved, depending on the type of preferred oriented Pt and KOH concentrat ion. Rotating ring-disc electrode data have shown that a higher amount of H2O2 is produced on one type of preferred oriented surface at all KOH concentrations. A complex reaction scheme has been used to evaluat e the electrochemical rate constants of the reaction steps at three pl atinum electrodes.