Localized Fluorination Triggering Intensified Internal Electric Field and Favored Reaction Thermodynamics in Carbon Nitride Homojunction for Efficient Photocatalytic CO ₂ Reduction

Abstract Constructing homojunction holds attractive promise for improving the photocatalytic performance of carbon nitride (g‐C ₃ N ₄ ), but it remains a great challenge to achieve an efficient conversion toward valuable chemicals. Herein, a local fluorination strategy is presented to improve the internal electric field (IEF) and simultaneously optimize the CO ₂ reduction thermodynamics of g‐C ₃ N ₄ homojunction (FLCN/HCN). It is found that F atoms doping in the low‐crystalline g‐C ₃ N ₄ (LCN) results in the Fermi level moving away from the conduction band, thus widening the Fermi level gap between F‐doped LCN (FLCN) and high‐crystalline g‐C ₃ N ₄ (HCN) and contributing to an intensified IEF in FLCN/HCN homojunction, which accelerates the interfacial charge transfer kinetics and achieves the spatial separation of photogenerated carriers. Density functional theory (DFT) calculation reveals that the synergistic interplay between the localized fluorination and homojunction construction decreases the formation energy barrier of ^* COOH and stabilizes the ^* CO intermediates, thus favoring the CO ₂ reaction thermodynamics and allowing CO ₂ to be smoothly reduced to CH ₄ . As expected, the integrated FLCN/HCN exhibits a high CH ₄ evolution rate of 20.33 µmol·g ⁻¹ ·h ⁻¹ and selectivity of 100% without adding sacrificial agent and co‐catalyst. This work provides an advanced design strategy for high‐performance homojunction photocatalysts by optimizing the kinetics and thermodynamics synergistically.