Selective Photocatalytic CO2 Reduction to CH4 on Tri-s-triazine-Based Carbon Nitride via Defects and Crystal Regulation: Synergistic Effect of Thermodynamics and Kinetics

Realizing the high selectivity of CH4 from the photocatalytic CO2 reduction reaction (CO2 RR) remains a great challenge owing to the lower efficiency of multi-electron transfer and the similar thermodynamic properties of CH4 and CO. Herein, nitrogen-deficient carbon nitride two-dimensional (2D) nanosheets were prepared via the high-temperature crystalline phase transformation process. Optimizing crystallinity enhances the in-plane polarization along the a-axis. Owing to the increased electron density of the N defect, the kinetic possibilities of CH4 production have increased. Furthermore, the potential energy of the mid-gap states introduced by the N defect favors the thermodynamics of CH4 production. The selectivity values of CH4 based on yield and electrons are 87.1 and 96.4%. This work unravels the mechanism to selectively produce CH4 from CO2 photoreduction through the crystalline phase and defect regulation and provides significant guidance for the rational design of CO2 reduction photocatalysts for selective CH4 production.