From our theoretical analysis, we come to the conclusion that the O-bound formate precursor species * OCHO, which is typically considered irrelevant for the CO producing catalyst Ag, should not only be present on the surface at low overpotentials during CO 2 ER, but is also likely playing an active role in promoting the selectivity of Ag towards CO production. In addition, the results strongly indicate that factors such as θ * H and solvation by surrounding water molecules will play an important role in controlling selectivity between the various CO 2 ER products. Calculation of activation barriers at constant potential and adjusted for activities of reactant and electrolyte species in order to simulate the conditions during electrocatalysis remains a challenge and there is a need for further development of computational methodologies for this purpose. Our approach demonstrates a constructive interplay between theory and experiments to advance the understanding of a complex system of high practical significance. The results highlight the need to study the catalyst surface in its operational steady state, both theoretically and experimentally, to understand the synergistic and competitive effects between the reaction species that ultimately result in the observed performance.