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 (VO) as an electrocatalyst for the efficient reduction of CO2 to yield CO in 1-butyl-3-methylimidazolium 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 VO 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.This work opens the way to realizing economic and efficient CO2 electrolysis of group II metals.