Activating Ionic Carbon Nitrides via Epitaxial Dyadic Coupling for Efficient Solar-Driven H₂O₂ Generation

Solar hydrogen peroxide synthesis is a sustainable alternative to the anthraquinone process, yet its efficiency is limited by charge separation and transport in polymeric photocatalysts. Ionic carbon nitrides like poly(heptazine imide) (PHI) offer tunable structures and electronic properties. Herein, we report an epitaxial strategy to construct a different π-conjugated CN species (C₁N₁) on potassium poly(heptazine imide) (KPHI), forming a dyadic charge-transfer nanostructure with strong interfacial coupling. Structural and spectroscopic analyses reveal that epitaxial registry at the interface induces orbital hybridization and a built-in electric dipole, driving directional electron transfer from KPHI to C₁N₁ while retaining holes within the PHI. The conduction band of the composite shifts upward, providing a thermodynamic benefit for the oxygen reduction reaction (ORR). Theoretical calculations confirm the thermodynamic driving force for electron transfer from KPHI to C₁N₁ and strong interfacial interactions. The optimized composite achieves an AQY of 63.9% at 410 nm without cocatalysts, approaching the optimum for stirred powder reactors. In-situ FTIR detects ∙O₂ ^- and ∙OOH intermediates and further reveals interfacial water reconstruction with increased free water molecules that facilitate proton supply. Mechanistic studies confirm a two-electron ORR pathway mediated by superoxide intermediates, promoted by the programmed charge-transfer landscape.