Electrocatalytic reduction of dioxygen at platinum particles dispersed in a polyaniline film

Platinum based electrocatalysts for the oxygen reduction reaction were prepared by electrodeposition of Pt particles in a polyaniline film acting as a convenient matrix to achieve low Pt loadings (from 11 to 600 mug cm(-2)). Using a rotating disc electrode or a rotating ring disc electrode allowed us to separate the different contributions in the overall reaction : diffusion of molecular oxygen in the electrolyte solution, diffusion inside the PAni film, adsorption process, and electron transfer. Koutecky-Levich analysis made possible to evaluate the kinetics parameters (total number of exchanged electrons, limiting current density, Tafel slope and exchange current density). These parameters vary with the Pt loading, displaying a steep increase at around 200 mug.cm(-2), above which the behavior of bulk platinum is found. At lower Pt loadings, the kinetics is controlled by a Temkin isotherm, and a large amount of hydrogen peroxide is formed. (C) 2000 Elsevier Science Ltd. All rights reserved.