Heat treatment effect of Pt-V/C and Pt/C on the kinetics of the oxygen reduction reaction in acid media

This work studies the heat treatment effect of carbon-dispersed platinum and platinum-vanadium alloys on the kinetics of the oxygen reduction reaction (ORR) in acid medium. The catalyst powders were subjected to heat treatments at three temperatures for 1 h. The electronic and structural features of the materials were characterized by X-ray diffraction (XRD) and in situ X-ray absorption near edge structure (XANES). The XANES results for the oxidized state composites showed an increase of the Pt 5d band occupancy with increased heat treatment temperature for the Pt/C catalyst, while no changes were noted for Pt-V/C for the same treatments. The electrochemical characteristics for the ORR were investigated by cyclic voltammetry and state-state polarization measurements. The results showed that the ORR takes place by the multi-electronic charge transfer process, following a four electron mechanism. The kinetics of the ORR was evaluated using Tafel diagrams. It was observed that the ORR activity of the Pt/C and Pt-V/C is enhanced with the increase of the heat treatment temperature. The catalytic activity of the materials was analyzed in terms of the electronic and structural properties of Pt in the metallic particles. (C) 2009 Elsevier Ltd. All rights reserved.