Promotional Role of a Cation Intermediate Complex in C2 Formation from Electrochemical Reduction of CO2 over Cu

Electroreduction of CO2 to C2 species was found to be promoted in the presence of large alkali metal cations, for example, Cs+. However, the origin of the promotional role remains unclear, and the complexity of structures and the intermediate–electrolyte interaction at the solid–liquid interface further pose enormous challenges. Here, with ab initio molecular dynamics simulation and free-energy sampling technology, the key step in producing C2 species, that is, CO dimerization to OCCO, was studied over Cu with an explicit solvent comprising Li+, K+, or Cs+. Results show that the free-energy barriers and reaction free energies of CO dimerization decrease in the presence of larger cations. Detailed analyses revealed that the dynamic cation intermediate complex is crucial for the promotion of C2 formation because larger cations can interact with two CO simultaneously, facilitating C–C bond formation. These insights obtained at the atomic level would facilitate further optimization of the electrolyte or catalysts for efficient CO2 conversion to C2 products.