Oxygen-mediated Lewis acid sites in polymeric carbon nitride for H₂O₂ photosynthesis

Photocatalysis for hydrogen peroxide (H₂O₂) photosynthesis, believed to be an alternative to the conventional anthraquinone method, has yet to overcome the sluggish proton-coupled electron transfer (PCET) process and unsatisfactory photocatalytic activity. Herein, an O-mediated Lewis acid site regulation strategy was proposed for polymeric carbon nitride (CN) with alkali metals (MA: Na, K, Rb, Cs) doped into the molecular structure. The alkali metals doped into the CN framework, particularly Cs, acting as strong electron donors, would significantly delocalize the π system in the CN framework for improved charge transfer ability, as well as induce strong electronic polarization across the O-mediated electronic bridge to generate electron-deficient O-adjacent C centers with enhanced Lewis acidity for molecular O₂ activation. Accordingly, Cs-OCN exhibits the smallest reaction free-energy change for the thermodynamically demanding *OOH → *H₂O₂ step, thereby favoring PCET-mediated H₂O₂ formation. As a result, Cs-OCN achieved an H₂O₂ production rate of 24,805 μmol g^-1 h^-1, along with an apparent quantum yield (AQY) of 49.3% at 420 nm. This study provides a possible dopant-mediated Lewis-acidity regulation strategy for efficient solar-to-chemicals conversion.