Hydroxyl-Bridged Phosphorus Doping-Induced Charge Polarization Enhancing Electron Delocalization for Efficient Photoreduction of CO2.

2D metal-free carbon nitride (CN) with extensive π-π conjugated structures suffers from electron localization due to pz orbital overlap, which severely limits its photocatalytic CO2 reduction performance. Herein, we propose an electron delocalization strategy via functional group-modified heteroatom doping. Through DFT screening and three-step copolymerization of phytic acid and urea, we precisely synthesized a 4-coordinated OH-bridged P-doped carbon nitride (CN-POH) featuring a unique 2N-P═OOH microstructure within heptazine units. CN-POH achieves a CO production rate of 1.82 mmol g-1 h-1, 15 times higher than pristine CN. Experimental and theoretical results reveal that P doping disrupts the π-π conjugation, triggering electron delocalization and transferring electrons to adjacent active N sites. The OH-modified P atom forms 2N-P═OOH coordination, inducing spatial charge polarization between VBM and CBM, which significantly enhances charge separation and electron delocalization. This unique structure also converts CO2 adsorption from physical to chemical mode under the effect of water solvents and facilitates CO2-to-CO conversion via hydrogen bonding with the water solvent. Collectively, CN-POH emerges as a highly efficient photocatalyst for CO2 reduction. This work provides a promising strategy for electron delocalization in CN materials and introduces a new reaction mechanism incorporating solvent molecule interactions.