In Situ Oxygen Vacancy Engineering for CO2 Electrolysis to Multi-Carbon Products with a Low CO Faradaic Efficiency of 4.5.

Copper (Cu) -based electrocatalysts have shown remarkable efficiency in promoting the carbon dioxide (CO2) reduction reaction (CO2RR) to multi-carbon (C2+) products. However, the challenge of minimizing the formation of the undesired byproduct carbon monoxide (CO) while enhancing the selectivity for C2+ products remains a significant hurdle. In this study, the designed and fabricated oxygen vacancy-rich Cu-based (OV-Cu/Cu2O) catalysts with the aim of suppressing CO production. The oxygen vacancies generated by the in situ cyclic voltammetry process are found to significantly enhance the electron density at the Cu site. Meanwhile, in situ Raman spectroscopy revealed that the enhanced production and adsorption of *CO resulted in reduced selectivity for CO, consequently accelerating the reduction of CO2 to C2+ products. As a result, the OV-Cu/Cu2O catalysts exhibit a low CO Faradaic efficiency (FE) of ≈4.5%, while achieving a high FEC2+/FECO ratio of up to 17.2 at a current density of -300 mA cm-2. These findings provide new insights into the introduction of oxygen vacancies in copper-based catalysts to suppress CO production.