Molecular Assembly Unlocks Dual‐Defect Synergy in Carbon Nitride for Efficient H ₂ O ₂ Photosynthesis

Abstract While promising for photocatalytic hydrogen peroxide (H 2 O 2 ) production, the performance of graphitic carbon nitride (g‐C 3 N 4 ) is curtailed by a central synthesis paradox: the mutually exclusive conditions required to simultaneously create its most effective dual active sites—nitrogen vacancies and cyano groups. Herein, this paradox is resolved with a molecular assembly‐molten salt coupling strategy, a precise bottom‐up approach enabling the one‐step, synergistic creation of K‐doped g‐C 3 N 4 with both defect types. This photocatalyst achieves an exceptional H 2 O 2 production activity of 2.65 mmol·g −1 ·h −1 , which is 6.2 and 3.0 times higher than that of pristine and physically‐ground K‐doped g‐C 3 N 4 , respectively. Characterization and theoretical calculations reveal that molecular assembly promotes K + interlayer embedding to facilitate charge migration, while the dual defects exhibit functional complementarity: nitrogen vacancies enhance O 2 adsorption, and cyano groups facilitate proton coupling. In situ analysis also confirms an easier O 2 activation effect and a lowered energy barrier for * OOH formation, ensuring high selectivity via a two‐step, single‐electron pathway. This study not only offers a route to rationally engineer dual‐defect sites in carbon nitride but also provides a generalizable strategy for designing other advanced photocatalysts.