Isolating the contributions of surface Sn atoms in the bifunctional behaviour of PtSn CO oxidation electrocatalysts

The bifunctional mechanism is well-acknowledged for the promoted CO oxidation on Pt-based bimetallic electrocatalysts. However, the direct identification of the active oxygenated species and the nature and electrochemistry of the second component are still a matter of debate. Herein, Sn-ad-Pt/C catalysts, where Sn ad-atoms are exclusively on the surface of Pt nanoparticles at low coverages ranging from 0.0033 to 0.2 monolayers to avoid sub-surface Sn and alloy formation, were prepared as a model system to resolve these issues using a surface organometallic chemistry approach. Effects of the Sn ad-atoms on CO oxidation were studied by CO stripping voltammograms as a function of Sn coverage. Using in situ XAS measurements, the Sn average oxidation state is estimated to increase from +0.2 to +3.1 as the potential increases from 0 to 0.8 V-RHE, with the number of the oxygen neighbours increasing stepwise. Pt-4.5-Sn-(OH)(1.5) is revealed as the active species responsible for the bifunctional mechanism at low overpotentials and is generated via a redox couple corresponding to Pt-4(.5)-Sn*/Pt-4(.5)-Sn-(OH)(1.5). (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study prepared Sn-ad-Pt/C catalysts using surface organometallic chemistry to investigate the active oxygenated species and nature of the second component in CO oxidation on Pt-based bimetallic electrocatalysts. The results revealed the role of Pt-4.5-Sn-(OH)(1.5) as the active species responsible for the bifunctional mechanism at low overpotentials.