EIS analysis of oxygen reduction reaction of Pt supported on different substrates

We investigated the kinetic and the mechanism of the oxygen reduction reaction (ORR) on Pt supported on two substrates (TiO2C and SnO2C) at different potentials. The platinum nanoparticles were synthesized by photo-reduction method. The morphology, size and composition of electrocatalysts were investigated through TEM and EDS analysis. The electrochemical properties of the materials were evaluated by cyclic voltammetry, linear sweep voltammetry and AC impedance spectroscopy. Electrochemical results were compared with Pt/C Etek commercial sample tested at same conditions. The Tafel slope values showed that the first electron transfer is the rate determining step. Pt/oxide-C samples show an improvement in the ORR catalytic activity compared to Pt/C Etek. The presence of oxide modifies the electronic properties of Pt related to a strong metal-substrate interaction. Two electric circuits were proposed to describe the impedance study of the ORR mechanism associated with at least the presence of two-electron reaction process involved.