Oxygen reduction reaction kinetics and mechanism on platinum nanoparticlesinside Nafion (R)

The aim of this work is to study kinetic parameters and the mechanism of th e oxygen reduction reaction (orr) on platinum nanoparticles supported on ca rbon, inside Nafion (R) (i.e. in PEMFC cathode conditions). Stationary and electrochemical impedance spectroscopy techniques were used to measure exch ange current densities, Tafel slopes, and reaction orders with respect to O -2 pressure and H+ activity. The platinum nanoparticle size effect was conf irmed. A specific low frequency inductive behaviour of the cathode impedanc e was observed. The latter demonstrates the presence of (at least) two elec trochemical steps in the orr mechanism. Secondly, de and ac modelling of th e reaction in a gas diffusion electrode is proposed in order to simulate cu rrent-potential curves and impedance spectra. This paper reveals that an EC E mechanism for oxygen reduction proposed by Damjanovic and coworkers on bu lk platinum in acidic medium is also valid for that on Pt nanoparticles. (C ) 2001 Elsevier Science B.V. All rights reserved.