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.