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

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/cm(2) at -1.27 V-RHE 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.