Abstract
Graphitic carbon nitride (g‐C
3
N
4
) is a promising semiconductor for solar‐to‐chemical conversion, yet its practical application in hydrogen peroxide (H
2
O
2
) photosynthesis is severely limited by inefficient charge separation and rapid electron–hole recombination. Herein, we report a synergistic multiscale engineering strategy to construct O‐doped g‐C
3
N
4
/CuO (CuO/O─C
3
N
4
) heterostructures designed for highly efficient photocatalytic H
2
O
2
production. By integrating atomic‐level oxygen doping with interface‐level CuO coupling, this strategy simultaneously regulates the intrinsic electronic structure of g‐C
3
N
4
and establishes an efficient interfacial charge‐transfer pathway. The optimized CuO/O─C
3
N
4
‐2 composite achieves a high H
2
O
2
concentration of 3978 μmol L
−1
under visible‐light irradiation in an acidic medium with HCOOH as a sacrificial agent, significantly outperforming pristine g‐C
3
N
4
. Comprehensive characterizations and theoretical insights reveal that the dual‐functionalization of oxygen‐induced electronic modulation and CuO‐mediated interfacial charge transfer synergistically promote carrier separation and facilitate the two‐electron oxygen reduction reaction. This work provides a sophisticated paradigm for the rational design of g‐C
3
N
4
‐based systems toward sustainable solar‐fuel production.