Impact of Support Physicochemical Properties on the CO Oxidation and the Oxygen Reduction Reaction Activity of Pt/SnO₂ Electrocatalysts

The interaction between Pt catalysts for the electrochemical oxygen reduction reaction (ORR) and corrosion-resistant SnO₂ supports has been studied by varying the Pt morphology and the SnO₂ physicochemical properties in a model electrode study. Different Pt morphologies ranging from isolated particles to thin films have been deposited by magnetron sputtering on oxidized and reduced SnO₂ model film electrodes as well as on glassy carbon (GC). Furthermore, three different surface probe reactions, namely the hydrogen underpotential deposition (H_upd), the CO oxidation, and the ORR have been studied to investigate the support influence on the Pt electrocatalytic properties. A marked effect of the type of the support, that is, tin oxide versus carbon, on the Pt electrochemically active surface area calculated from the H_upd charge was observed. Furthermore, a pronounced CO oxidation activity of Pt deposited on SnO₂ supports was observed compared to that of Pt supported on GC. The intrinsic ORR activities of Pt/SnO₂ and Pt/GC catalysts varied with both the Pt morphology and the SnO₂ stoichiometry. While very similar ORR activities of all catalysts were found at high Pt loadings where an extended surface Pt morphology is expected, a strong support dependence was observed for isolated Pt particles at low Pt loadings. Pt nanoparticles supported on reduced SnO₂ and on GC showed very comparable ORR activities, about five times higher than that of Pt nanoparticles on oxidized SnO₂. Postmortem X-ray photoelectron spectroscopy investigations revealed that the reduced ORR activity of the latter catalysts can be explained with a stronger oxidation of Pt nanoparticles when supported on oxidized SnO₂. This finding highlights the fundamental importance of tailoring the oxide support properties to maximize the Pt electrocatalyst performance