Influence of the proton transport on the ORR kinetics and on the H2O2 escape in three-dimensionally ordered electrodes

• Protons are involved in the rate determining step of the ORR in acidic media.
• The kinetics of the ORR involving protons is approximately 105 times faster than the one involving water dissociation.
• The increase of the electrolyte pH results in a pronounced maximum in the H2O2 escape current, which may be explained by slowing down the reduction of the Pt surface oxide.

In this study, we use rotating ring disc electrode measurements to investigate the influence of the proton transport on the kinetics of the oxygen reduction reaction (ORR) in a 3D nanostructured catalytic layer based on Pt nanoparticles supported on vertically aligned carbon nanofibers. The results confirm that protons are involved in the rate determining step of the ORR in acidic media. For pH ≥ 3, the ORR occurs in two successive reduction waves. The first current plateau is limited by the proton diffusion and is followed by the second reduction wave attributed to the mechanism involving water dissociation. The shape of the H2O2 escape current curve is strongly affected by the pH of the solution and shows a pronounced maximum when the pH value is increased. These experimental features are discussed with the help of a kinetic model.