Oxygen electrocatalysis on thin porous coating rotating platinum electrodes

This work discusses the electrocatalysis of the oxygen reduction reaction o n platinum on carbon thin porous coating rotating disk electrodes in alkali ne and acid media. The electrochemical techniques considered are cyclic vol tammetry, steady state polarization and impedance spectroscopy. Both the de and ac polarization results are analyzed and simulated with the thin film/ flooded agglomerate model. Cyclic voltammetry allows an inspection of the c rystal facet structure of the Pt particles and the determination;;of effect ive surface areas which are lower than those determined from X-ray diffract ion techniques or transmission electron microscopy. The de polarization and impedance results show clearly a duplication of the Tafel slope due to str uctural effects on the porous electrode. Experiments in alkaline solutions show that in this medium there is an important contribution from the carbon to the kinetics of the reaction, which is negligible in acid medium. The e ffect of Pt particle size on the oxygen reduction electrocatalysis in both electrolytes is correlated with the predominant facets of the platinum crys tallites. (C) 1998 Elsevier Science Ltd. All rights reserved.