Polarized Electronic Structure of Carbon Nitride Enhances Selective Triphase Continuous-Flow Photosynthesis of Hydrogen Peroxide

The H 2 O 2 photosynthesis efficiency by carbon nitride (CN) via a two-electron oxygen reduction reaction (ORR) is limited by insufficient charge separation, sluggish O 2 supply in aqueous solution, and difficulty in O 2 adsorption and activation. Here, we modulated CN with sulfonic acid and cyano groups, which impart multiple favorable electronic properties for H 2 O 2 photogeneration, including broadened light absorption, enhanced charge separation due to the polarized electronic structure, and improved O 2 adsorption and activation. H 2 O 2 photogeneration experiments showed that it delivered a 41-fold enhancement in H 2 O 2 yield, reaching a value of 44.5 mmol g –1 h –1 with a high AQY of 36.5% at 400 nm and a high selectivity of >94%. Experiments and density functional theory (DFT) calculations revealed the preferential two-step 1e ORR mechanism. Further fabrication of a triphase flow photoreactor by immobilizing the functionalized CN on a gas diffusion layer achieved fast O 2 supply and continuous-flow H 2 O 2 photogeneration with a 4 times higher yield of 171 mmol m –2 in 6 h than in a two-phase system. As a proof-of-concept, continuous-flow H 2 O 2 photogeneration was further coupled with organic synthesis exemplified by furfuryl alcohol photooxidation conversion. This work solves multiple important issues of CN in H 2 O 2 photogeneration by combining electronic polarity modulation with a triphase continuous-flow photoreactor design.