Bimetallic electrocatalysts provide a promising strategy for improving performance, especially in the enhancement of selectivity of CO2 reduction reactions. However, the first step of CO2 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 CO2 adsorption and activation on AgCu exposed to CO2 with and without H2O 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 CO2 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 CO2-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.
Keywords: CO2 activation; CO2 adsorption; ambient pressure XPS (APXPS); density functional theory (DFT); surface reconstruction.