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

Abstract

The interaction between Pt catalysts for the electrochemical oxygen reduction reaction (ORR) and corrosion-resistant SnO 2 supports has been studied by varying the Pt morphology and the SnO 2 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 SnO 2 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 SnO 2 supports was observed compared to that of Pt supported on GC. The intrinsic ORR activities of Pt/SnO 2 and Pt/GC catalysts varied with both the Pt morphology and the SnO 2 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 SnO 2 and on GC showed very comparable ORR activities, about five times higher than that of Pt nanoparticles on oxidized SnO 2 . 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 SnO 2 . This finding highlights the fundamental importance of tailoring the oxide support properties to maximize the Pt electrocatalyst performance.

The effect of SnO2(110) supports on the geometrical and electronic properties of platinum nanoparticles

“…Our results match different experimental observations/tendencies; our results show that as the size of the nanoparticle decreases, there is a tendency for the nucleophilic species to interact more stably on Pt-nanoparticles supported. A similar tendency was observed for Pt-nanoparticles supported on carbon [40], glassy carbon [81], and Nb-doped SnO 2 [25]. The low activity of Pt-nanoparticles of ca.…”

“…The low activity of Pt-nanoparticles of ca. 2.0 nm supported on SnO 2 is due to the strong interaction of OH species [40], and that the OH interaction on reduced SnO 2 is weaker than on Pt/SnO 2 [40]. Additionally, our results can explain the fact that nanoparticles supported on reduced SnO 2 and Nb-doped SnO 2 exhibited increased ORR activity, which so far was related to the increased electronic conductivity due to Nb doping than the Pt/SnO 2 systems [22,25].…”

“…Our results agree and explain the low activity exhibited by Pt-nanoparticles of ca. 2 nm supported on SnO 2 [40]. Experimentally, the strong interaction of oxygenated species on Pt-nanoparticles with diameters of 2 nm supported on SnO 2 is responsible for the low ORR activity compared to those supported on glassy carbon [40].…”

“…2 nm supported on SnO 2 [40]. Experimentally, the strong interaction of oxygenated species on Pt-nanoparticles with diameters of 2 nm supported on SnO 2 is responsible for the low ORR activity compared to those supported on glassy carbon [40]. The ORR activity increased only after extended Pt regions were formed on oxidized SnO 2 due to the large Pt loadings, where the effect of the support is minimal.…”

“…Moreover, high Pt loadings on oxidized SnO 2 , reduced SnO 2 , and graphene all showed comparable ORR. Only in the case of oxidized SnO 2 , decreasing the Pt loading led to lower ORR activity, which was attributed to stronger adsorption of oxygenated species [40]. It was shown that electronic metal-support interactions can affect the charge of the catalytically active outer surface of nanoparticles [41].…”