Mechanistic Insights into Enhanced CO ₂ Conversion to Fuels and Chemicals with O‐Doped g‐C ₃ N ₄

Abstract In this work, bare and O‐doped g‐C 3 N 4 nanosheets were synthesized. The results show that the structure of bare and O‐doped g‐C 3 N 4 (OCN) nanosheets are layered and the absorption of visible light increases after O‐doping. Density function theory calculations demonstrate that the oxygen atom is replaced at the edge site of g‐C 3 N 4 . The reaction pathway of CO 2 reduction to fuel/chemicals on the OCN surface is as follows: CO 2 → HCOO→ HCOOH→ HCO + H 2 O→ H 2 CO→ H 2 COH→ H 3 COH→ CH 3 + H 2 O→ CH 4 . The main product on the OCN and CN surfaces are methane and methanol, respectively. The Gibbs activation energy of CH 3 OH formation on the CN and OCN surfaces are 1.72 and 0.14 eV, respectively. The rate‐determining step on the OCN surface is HCOOH→ HCO + H 2 O, whereas on the CN surface is CH 3 OH formation from the H 3 CO intermediate. Therefore, the Gibbs activation energy on the O‐doped g‐C 3 N 4 decreases for the methanol production in comparison with the bare g‐C 3 N 4 . In general, the O‐doping of g‐C 3 N 4 improves the photocatalytic activity through the decrement in the band gap and enhances the reaction rate of CO 2 conversion to fuels/chemicals.