Poisoning effect of adsorbed CO during CO₂ electroreduction on late transition metals

Copper cathodes, at sufficiently negative potentials, are selective for hydrocarbon production during the electrochemical reduction of carbon dioxide. Other metals, such as Pt, Fe, Ni and Co, produce low to zero hydrocarbons. We employ density functional theory to examine the coverage of reaction intermediates under CO₂ electroreduction conditions. A detailed thermodynamic analysis suggests that a high coverage of adsorbed CO at relevant reduction potentials blocks the metal surface sites for H adsorption, preventing C-H bond formation. The potential-dependent energetics of H adsorption and CO formation are highly sensitive to the surface coverage of the adsorbed species. The formation of surface carbon as a competing adsorption intermediate is also explored at relevant reduction potentials. CO₂ electroreduction to hydrocarbons over metals active for the thermal reduction process (Fe, Ni, Co, Pt) would require a H supply for C-H bond formation that is competitive with CO* and C* at the surface.