Engineering surface bromination in carbon nitride for efficient CO2 photoconversion to CH4

The direct conversion of CO2 into reusable CH4 fuel by solar energy can effectively solve the problems of energy crisis and carbon emissions. However, the challenge of photocatalytic CO2 reduction to produce CH4 is still low conversion efficiency and poor selectivity. Here, surface brominated carbon nitride (named CNBr) is fabricated for stable and efficient photocatalytic CO2 reduction to produce CH4 with a rate of 16.68 μmol h-1 g-1 (70.27 % selectivity). Br atom in CNBr can substitute the N atom in the tri-s-triazine unites, which promotes local charge separation, narrows band gap and deepens the conduction band of CNBr. Benefiting from Br as active sites, CO2 can be enriched on the catalyst surface, and localized photogenerated electrons can activate the adsorbed CO2 to form CH4 through subsequent hydrogenation. Density functional theory results suggest that Br doping can effectively reduce the energy barrier of the rate-limiting step, accelerate the reaction, and induce the formation of *CHO, thereby improving the selectivity of CH4. This work reveals that surface modification can simultaneously increase the activation site of CO2 adsorption activation, enhance light absorption and accelerate charge, laying a solid foundation for the future design of carbon nitride based photocatalyst with high performance.