Why Including Solvation is Paramount: First-Principles Calculations of Electrochemical CO₂ Reduction to CO on a Cu...

Electrochemical reduction reaction of CO₂ (eCO₂RR) to produce valuable chemicals offers an attractive strategy to solve energy and environmental problems simultaneously. We have mapped out entire reaction pathways of eCO₂RR to CO on Cu(100), including all intermediates and transition states using first-principles simulations. To accurately account for the solvent effect, the reaction was investigated with and without explicit water molecules, highlighting the limitations of the often (mis)used vacuum reaction pathway simplification. The results show that the reduction reaction was initiated under neutral pH conditions at an applied potential of -0.11 V (RHE, reversible hydrogen electrode) and all elementary reactions were thermodynamically favorable, while an applied potential of -1.24 V is required to ensure that all reactions exhibit spontaneous behavior. Detailed analysis revealed that solvation significantly influences the stability of the adsorbates and intermediates. Its inclusion notably alters the calculated reaction kinetics and energetic parameters by lowering the barrier energies and Gibbs free energies of all reactions. CO production proceeded mainly via the COOH* pathway (CO₂ →trans-COOH*→cis-COOH*→CO*+OH*→CO*→CO). The use of water as a more sustainable and cost-effective solvent is compared to other options such as organic solvents, ionic liquids and mixed solvent systems, which are less sustainable and more expensive.