Tuning local carbon active sites saturability of graphitic carbon nitride to boost CO2 electroreduction towards CH4

Abstract New approach to activating carbon active sites to facilitate the electroconversion of CO2 through N-vacancy engineering is proposed and confirmed by the density functional theory calculations and experimental results. N-vacancy engineered graphitic C3N4 (g-C3N4) is identified as an efficient electrocatalyst to boost CH4 formation owing to the three-coordinating to two-coordinating transition of the carbon atoms that surround N vacancies. The defected g-C3N4 (DCN) exhibits a 44% faradaic efficiency with a CH4 partial current density of 14.8 mA/cm2 at −1.27 VRHE in 0.5 M KHCO3 electrolyte, exceeding all the reported carbon-based materials and even being comparative to Cu-based electrocatalysts. Creation of more unsaturated carbon atoms enables the harmonic energy overlap near band gap edge between DCN and *CO, accounting for an improved strength of *CO on DCN, a lower energy barrier and an enhanced CO2RR to form CH4. This strategy holds the promise for tuning atomic configuration to enhance activity of catalyst.