The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous...

Carbon dioxide (CO₂ ) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu₂ O) is a promising catalyst for CO₂ reduction as it can convert CO₂ into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu₂ O remains under debate because of the complex surface structure of Cu₂ O under reducing conditions, leading to limited guidance in designing improved Cu₂ O catalysts. This paper describes the functionality of surface-bonded hydroxy groups on partially reduced Cu₂ O(111) for the CO₂ reduction reaction (CO₂ RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO₂ RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO₂ RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination-unsaturated Cu (Cu_CUS ) sites stabilizes surface-adsorbed COOH*, which is a key intermediate during the CO₂ RR. Moreover, the CO₂ RR was evaluated over Cu₂ O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu₂ O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO₂ RR and suppress the HER.