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.