A STUDY OF CATHODIC OXYGEN REDUCTION AT PLATINUM USING MICROELECTRODES

The cathodic reduction of oxygen has been investigated in neutral and basic aqueous solutions at a Pt rotating-disc electrode and Pt microelectrodes. The limiting current densities for the reduction waves at the various Pt electrodes have been interpreted by constructing a plot of the apparent number n(app) of electrons involved in the reduction versus the mass-transfer coefficient k(m) for the experimental conditions. It is shown that n(app) is a strong function of k(m) and the reduction changes from a four-electron to a two-electron process with increasing rate of mass transport. Hydrogen peroxide is the major product from oxygen reduction in conditions with large k(m). This provides new evidence for the mechanism of oxygen reduction at Pt and also has consequences for practical electrochemistry.