Synergy between a Silver-Copper Surface Alloy Composition and Carbon Dioxide Adsorption and Activation.

Bimetallic electrocatalysts provide a promising strategy for improving performance, especially in the enhancement of selectivity of CO reduction reactions. However, the first step of CO activation on bimetallic materials remains obscure. Considering bimetallic silver-copper (AgCu) as an example, we coupled ambient pressure X-ray photoelectron spectroscopy (APXPS) and quantum mechanics (QM) to examine CO adsorption and activation on AgCu exposed to CO with and without HO at 298 K. The interplay between adsorbed species and the surface alloy composition of Cu and Ag is studied in atomic details. The APXPS experiment and density functional theory (DFT) calculations indicate that the clean sample has a Ag-rich surface layer. Upon adsorption of CO and surface O, we found that it is thermodynamically more favorable to induce subsurface Cu atoms substitution for some surface Ag atoms, modifying the stability and activation of CO-related chemisorbed species. We further characterized this substitution effect by correlating the new adsorption species with the observed binding energy (BE) shift and intensity change in APXPS.