Abstract
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.