Cooperative Catalysis Over a Potassium Phosphotungstate/Carbon Nitride Nanosheet S‐Scheme Heterojunction for Boosted Photocatalytic CO ₂ Reduction

Carbon nitride is a promising photocatalyst for CO ₂ reduction; however, its performance is limited by rapid charge‐carrier recombination and insufficient CO ₂ adsorption and activation. Herein, a potassium phosphotungstate/carbon nitride nanosheet (KPW/CNS) heterojunction was constructed through a facile electrostatic assembly strategy for photocatalytic CO ₂ reduction. The optimized photocatalyst (5KPW/CNS) exhibited CH ₄ and CO evolution rates of 6.3 and 9.3 μmol g ⁻¹  h ⁻¹ , respectively, corresponding to a CH ₄ selectivity of 40% and excellent photostability. In comparison, pristine CNS produced only 0.4 μmol g ⁻¹  h ⁻¹ of CH ₄ , and showed a much lower CH ₄ 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 CO ₂ adsorption and activation to form *CO intermediates, whereas KPW facilitates the subsequent hydrogenation of *CO toward *CHO, *CH ₂ O, and ultimately CH ₄ . This synergistic interaction promotes the CO ₂ ‐to‐CH ₄ conversion pathway and accounts for the enhanced CH ₄ selectivity of the KPW/CNS heterojunction.