The role of site coordination on the CO2 electroreduction pathway on stepped and defective copper surfaces

Abstract

Copper (Cu) electrocatalysts have been known as the only single-metal catalysts able to reduce carbon dioxide (CO₂) further than products such as CO and HCOOH with considerable efficiency. However, the product distribution depends on the type of employed Cu surface, and hence, reaction mechanisms for such wide product distributions remain under debate. Here, we have employed density functional theory calculations to investigate the interaction between Cu surfaces with different levels of adsorption site coordination and several intermediates that could be present in the CO₂ reduction towards CO, HCOOH, CH₄, and CH₃OH. We found that decreasing the adsorption site coordination strengthens the adsorption and interaction energies of all intermediates, but the magnitude of such a coordination effect is different from one adsorbate to another. Therefore, this effect leads to the prediction of coordination-dependent reaction pathways, e.g., HCOOH formation could happen through COOH (HCOO) intermediates if the reaction proceeds on step (terrace) sites of a Cu(533) surface. Moreover, we have tested if different solvation corrections could change the reaction pathways, onset potentials, or potential-determining steps for a given product. Interestingly, we found that a change in the solvation correction makes the reaction pathway predicted solely with thermodynamic arguments to be in better agreement with experimental findings, but this effect does not occur for surfaces with lower coordination sites. Thus, it could indicate the importance of kinetic arguments to explain some inconsistencies between thermodynamic pathways and experimental observations.