Enhancement in ethanol electrooxidation by SnO_x nanoislands grown on Pt(111): Effect of metal oxide-metal interface sites

An integrated surface science and electrochemistry approach has been used to prepare and characterize SnO_x/Pt(111) model catalysts and evaluate their electrochemical activity for the ethanol oxidation reaction (EOR). Nanoislands of SnO_x are deposited onto the Pt(111) by reactive layer assisted deposition in which Sn metal is vapor deposited onto a Pt(111) surface precovered by NO₂. X-ray photoelectron spectroscopy (XPS) shows that the SnO_x islands are highly reduced with Sn²⁺ being the dominant chemical species. After exposing the SnO_x/Pt(111) surface to H₂O or an electrolyte solution, XPS provides evidence for a significant amount of H₂O/OH adsorbed on the reduced SnO_x surfaces. Electrochemical testing reveals that the catalytic performance of Pt(111) toward ethanol electrooxidation is significantly enhanced with SnO _x islands added onto the surface. The enhanced EOR activity is tentatively attributed to the efficient removal of CO_ads-like poisoning species at Pt sites by oxygen-containing species that are readily formed on the SnO_x nanoislands. Moreover, the strong dependence of the EOR activity on SnO_x coverage provides experimental evidence for the importance of SnO_x-Pt interface sites in the EOR.