Electrocatalytic Reduction of CO₂ to CO with Almost 100% Faradaic Efficiency Using Oxygen-Vacancy Enriched Two-Dimensional MgO

The design and development of cheap, abundant, and efficient electrocatalysts for selective CO₂ electroreduction is highly desirable yet remains an ongoing challenge. Herein, we report on our discovery of the use of two-dimensional MgO rich in oxygen vacancies (V_O) as an electrocatalyst for the efficient reduction of CO₂ to yield CO in 1-butyl-3-methylimi-dazolium hexafluorophosphate dissolved in acetonitrile. The faradaic efficiency toward CO reaches as high as 99.6 ± 0.24% with a current density of up to 40.8 mA cm⁻². Density functional theory calculations illustrate that the introduction of V_O in MgO substantially lowers the reaction-free energy for the transformation of *COO⁻ to *COOH, the potential determining step, which greatly boosts CO₂ conversion efficiency.