Kinetics and mechanism of the oxygen electroreduction reaction on faceted platinum electrodes in trifluoromethanesulfonic acid solutions

The kinetics of the oxygen electroreduction reaction (OERR) were investigated on (1 1 1)-type and (1 0 0)-type faceted, and polycrystalline platinum electrodes in aqueous (0.05–1.0)m trifluoromethanesulfonic acid (TFMSA) using the rotating disc and ring-disc electrode techniques at 25°C. Reaction orders with respect to oxygen close to either 1/2 or 1 were found, depending on the TFMSA concentration and platinum surface morphology. At all TFMSA concentrations the formation of H₂O₂ was enhanced at (1 0 0)-type platinum surfaces. The difference in the electrocatalytic activity of platinum surfaces can be explained through data derived from the OERR formalism proposed by Damjanovicet al. The rate of the direct O₂ to H₂O electroreduction reaction increased steadily with the cathodic overvoltage irrespective of the platinum surface morphology, whereas a maximum H₂O₂ formation rate was found at about 0.5 V, depending on the TFMSA concentration. The H₂O₂ decomposition rate on (1 0 0)-type platinum electrode yielding H₂O approached zero within a certain potential range.