Role of SnO 2 in the Bifunctional Mechanism of CO Oxidation at Pt‐SnO 2 Electrocatalysts

• Published in: ChemElectroChem Vol. 8; no. 13; pp. 2572 - 2582
• Main Authors: Huang, Haoliang, Hayes, Edward T. C., Gianolio, Diego, Cibin, Giannantonio, Hage, Fredrik S., Ramasse, Quentin M., Russell, Andrea E.
• Format: Journal Article
• Language: English
• Published: 01.07.2021
• ISSN: 2196-0216; 2196-0216
• DOI: 10.1002/celc.202100642

Abstract Pt‐Sn bimetallic catalysts, especially Pt‐Sn alloys, are considered highly CO‐tolerant and are thus candidates for reformate derived hydrogen oxidation and for direct oxidation of fuel cell molecules. However, it remains unclear if this CO‐tolerance originates from Sn in the Pt‐Sn alloy or whether SnO 2 , present as a separate phase, also contributes. In this work, a carbon‐supported Pt‐SnO 2 was carefully synthesized to avoid the formation of Pt‐Sn alloy phases. The resulting structure was analysed by scanning transmission electron microscopy (STEM) and detailed X‐ray absorption spectroscopy (XAS). CO oxidation voltammograms of the Pt‐SnO 2 /C and other SnO 2 ‐modified Pt surfaces unambiguously suggest that a bifunctional mechanism is indeed operative at such Pt‐SnO 2 catalysts for stable CO oxidation at low overpotentials. The results from these studies suggest that the bifunctional mechanism can be attributed to the co‐catalysis role of SnO 2 , in which the surface hydroxide of SnO 2 (Sn‐OH) reacts with CO adsorbed on Pt surface (Pt‐CO ads ) and regenerates via a Sn II /Sn IV reversible redox couple (−0.2–0.3 V vs . reversible hydrogen electrode).