Pathways for the Formation of C₂₊ Products under Alkaline Conditions during the Electrochemical Reduction of CO₂

Establishing how Cu facilitates the electrochemical CO<sub>2</sub> reduction reaction (CO2RR) to C<sub>2+</sub> products remains a critical challenge. Under typical reaction conditions, the pH near the electrode is considerably more alkaline than that in the bulk due to mass transport limitations. Challenges with probing alkaline pathways using computational methods have limited understanding of the CO2RR under experimentally relevant conditions. In this work, using the Volmer reaction on Cu (100), we demonstrate that predicted activation barriers can substantially differ between acidic and alkaline pathways. We compute reaction energetics for alkaline *CO protonation and find that, while the formation of *CHO is preferred thermodynamically, the formation of *COH is favored kinetically at high overpotential. However, we find formation of *CHO via reaction of *H and *CO feasible at room temperature. Further, we report potential-dependent energetics for forming the first C-C bond in CO2RR and find that CO dimerization likely dominates. Finally, we investigate how long-range van der Waals interactions impact our results by comparing to the meta-GGA B97M-rV.