Oxygen reduction reaction kinetics and mechanism on platinum nanoparticles inside Nafion®

The aim of this work is to study kinetic parameters and the mechanism of the oxygen reduction reaction (orr) on platinum nanoparticles supported on carbon, inside Nafion® (i.e. in PEMFC cathode conditions). Stationary and electrochemical impedance spectroscopy techniques were used to measure exchange current densities, Tafel slopes, and reaction orders with respect to O2 pressure and H+ activity. The platinum nanoparticle size effect was confirmed. A specific low frequency inductive behaviour of the cathode impedance was observed. The latter demonstrates the presence of (at least) two electrochemical steps in the orr mechanism. Secondly, dc and ac modelling of the reaction in a gas diffusion electrode is proposed in order to simulate current–potential curves and impedance spectra. This paper reveals that an ECE mechanism for oxygen reduction proposed by Damjanovic and coworkers on bulk platinum in acidic medium is also valid for that on Pt nanoparticles.