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.