Alkali Cations Promote CO ₂ Electroreduction on Cu(100) Surfaces under Acidic Conditions by Suppressing Surface Hydrogen Passivation: A Multiscale Modeling Perspective

High Resolution Image Download MS PowerPoint Slide The promotional effect of cations on the CO 2 reduction reaction (CO 2 RR) on Cu is well-established experimentally, yet the underlying mechanism remains debated. This is further complicated by an underexplored factor: in acidic solution, the Cu surface may be covered by a H adlayer rather than being pristine. We employ a multiscale modeling approach to investigate how the H adlayer and electric double layer environment affect CO 2 RR activity on Cu(100). GC-DFT calculations demonstrate that the H adlayer on Cu lowers the d-band center of Cu, attenuating CO 2 RR activity and correctly identifying CO 2 chemisorption as the rate-limiting step. This H-passivated surface provides a novel lens through which to view the cation effects. Molecular dynamics simulations reveal that the direct Cs + stabilization of intermediates is a minor effect. More importantly, Cs + thermodynamically favors the transition to lower H coverage and suppresses H 3 O + adsorption on the Cu surface. We thus propose a dual-role mechanism: alkali cations promote CO 2 RR also by acting as depassivants that reduce H coverage, restoring the catalytic activity of the Cu surface for the CO 2 RR.