Electrode reaction induced pH change at the Pt electrode/electrolyte interface and its impact on electrode processes

The change of local pH at electrode/electrolyte interface (pHs) induced by the electrode reactions such as under potential deposition of H (UPD-H), the reduction of Pt oxide as well as oxygen reduction reaction (ORR) at Pt electrode and its effect on such processes have been systematically examined in solutions with pH from 1 to 13. Distinct changes of the numbers, position and shapes of the current waves for such electrode processes with the solution pH, potential scan rate and electrode rotation speed are observed in unbuffered solutions with low H+ (or OH−) concentration. It can be explained by the variation of pHs due to the electrode reactions, and the pHs variation induced change of adsorbate coverage, the thermodynamic equilibrium and the reaction kinetics of the above mentioned electrode processes. The polarization curves of the ORR at Pt Electrode also change sensitively with solution pH. The onset potential for ORR matches well with that for Pt–OHad/Oad reduction under all local pH conditions, indicating that the inhibition of O2 adsorption by OHad/Oad at Pt surface is probably the origin of the high activation overpotential at the onset potential for ORR at Pt electrode.