Copper catalyst surface engineering with CO* adsorbates*

The electrochemical reduction of CO₂ with Cu-based catalysts depends intimately on the instantaneous local chemical environment of the catalyst-electrolyte interface. This microenvironment fluctuates according to the surface concentration of competing reaction intermediates and the applied electrode potential. In practice, disentangling these factors is exceedingly challenging, yet they critically determine catalyst efficiency and selectivity. To address this we use a newly developed grand canonical quantum-classical hybrid method (ESM-RISM), which treats the solvent with atomic accuracy at reasonable computational cost. This method allows us to quantify the complex interdependence between electrode potential, CO∗ coverage, and the interfacial field strength. We show that the oft-overlooked CO∗ coverage effect in fact strongly influences the field strength, with a magnitude change exceeding 1V/Å at certain potentials; among other effects, this change should lower the CO-dimerization barrier that dictates selectivity toward multi-carbon products. Beyond showcasing the importance of surface coverage for CO₂R, our results highlight the power of surface additives to modulate interfacial fields toward tailored electrochemical pathways.