CO adsorption free energy ( \(\Delta {G}_{{\rm{C}}{\rm{O}}}^{{\rm{a}}{\rm{d}}{\rm{s}}}\) ) has been proposed as a key descriptor for CO2 electroreduction (CO2R), yet its role remains unverified due to the lack of experimental methods capable of probing \(\Delta {G}_{\mathrm{CO}}^{\mathrm{ads}}\) under reaction conditions. Here we present a kinetic model combined with a rotating ring-disk electrode voltammetry method to estimate \(\Delta {G}_{\mathrm{CO}}^{\mathrm{ads}}\) on the active sites of various CO-producing catalysts during CO2R. Our results reveal that CO adsorption is influenced by multiple factors including catalyst type, cation identity and concentration, applied potential and surface structure. Notably, the measured difference in \(\Delta {G}_{\mathrm{CO}}^{\mathrm{ads}}\) between Au and Cu at CO2R-to-CO active sites is small, suggesting that the \(\Delta {G}_{\mathrm{CO}}^{\mathrm{ads}}\) of CO-producing active sites alone cannot account for Cu’s unique ability to catalyse CO2 into multicarbon products at appreciable rates. This study highlights the complexity of evaluating CO adsorption under CO2R conditions and introduces a robust experimental framework for quantifying \(\Delta {G}_{\mathrm{CO}}^{\mathrm{ads}}\) on CO-producing catalysts.
