Cooperative Catalysis Over a Potassium Phosphotungstate/Carbon Nitride Nanosheet S-Scheme Heterojunction for Boosted...

Carbon nitride is a promising photocatalyst for CO₂ reduction; however, its performance is limited by rapid charge-carrier recombination and insufficient CO₂ adsorption and activation. Herein, a potassium phosphotungstate/carbon nitride nanosheet (KPW/CNS) heterojunction was constructed through a facile electrostatic assembly strategy for photocatalytic CO₂ reduction. The optimized photocatalyst (5KPW/CNS) exhibited CH₄ and CO evolution rates of 6.3 and 9.3 μmol g^-1 h^-1, respectively, corresponding to a CH₄ selectivity of 40% and excellent photostability. In comparison, pristine CNS produced only 0.4 μmol g^-1 h^-1 of CH₄, and showed a much lower CH₄ selectivity of 7.0%. Combined X-ray photoelectron spectroscopy, Kelvin probe force microscopy and density functional theory calculations revealed the formation of built-in electric field at the KPW/CNS interface, which drives an S-scheme charge-transfer pathway and promotes efficient spatial separation of photogenerated charge carriers. More importantly, mechanistic investigations demonstrated a cooperative catalytic pathway involving both components of the heterojunction. CNS primarily acts as the electron-enriched site for CO₂ adsorption and activation to form *CO intermediates, whereas KPW facilitates the subsequent hydrogenation of *CO toward *CHO, *CH₂O, and ultimately CH₄. This synergistic interaction promotes the CO₂-to-CH₄ conversion pathway and accounts for the enhanced CH₄ selectivity of the KPW/CNS heterojunction.