Precisely doping the surface of tin-based electrocatalysts for improved CO2 conversion to liquid chemicals

Doping tin catalysts with sulfur can improve the electrochemical CO2 conversion into formate/formic acid, but the lack of composition-dependent activity trends hinders further catalyst development. Here, we precisely controlled the composition of sulfur-doped Sn catalysts to show that sulfur doping only improves CO2 conversion over a very narrow composition range, achieving maximum activity at 1.4 at% S. In situ Raman spectroscopy indicted working catalysts were in a primarily metallic state (e.g. S-Sn), and we achieved some of the highest reported partial current densities in both H-cell and full-cell electrolyzer configurations. Density Functional Theory calculations predicted S atoms preferentially occupied the catalyst surface and improved CO2 reduction by localizing charge density at the catalyst/intermediate interface, which stabilized the *OCOH intermediate and lowered the CO2 conversion thermodynamic barrier. Our work quantifies the composition-dependent influence of S dopants on Sn-based CO2 reduction catalysts and provides a pathway for maximizing their CO2 conversion activity.