Molecular Assembly Unlocks Dual-Defect Synergy in Carbon Nitride for Efficient H₂O₂ Photosynthesis

While promising for photocatalytic hydrogen peroxide (H₂O₂) production, the performance of graphitic carbon nitride (g-C₃N₄) 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-C₃N₄ with both defect types. This photocatalyst achieves an exceptional H₂O₂ 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-C₃N₄, 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 O₂ adsorption, and cyano groups facilitate proton coupling. In situ analysis also confirms an easier O₂ 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.