Spatially confined proton-coupled electron transfer in functional microcavities for photocatalytic H2O2 production in pure water

Abstract

Photocatalytic synthesis of H₂O₂ from O₂ and H₂O offers a sustainable alternative to conventional production methods, although its efficiency remains severely limited by sluggish and mismatched proton-coupled electron transfer (PCET), arising from inefficient charge separation, non-selective reaction pathways and suboptimal local microenvironments. To address these challenges, we design a series of well-defined donor–acceptor (D–A) conjugated polymers featuring pyrene-based donor units and electron-deficient heterocyclic acceptors—either pyrimidine (PyM) or pyridazine (PyD). Moreover, confined polymeric microcavities featuring atomically precise functional sites are constructed through strategic carboxyl functionalization (PyD-COOH). Our findings reveal that the adjacent nitrogen atoms in pyridazine function as effective electron acceptors and active centers for dioxygen activation, while the carboxyl group serves as a proton-relay moiety and simultaneously enhances oxygen adsorption. This precisely arranged spatial architecture enables confined transport of electrons, protons, and O₂ molecules within the catalytic microcavity, facilitating a highly efficient and well-organized PCET process. The optimized PyD-COOH photocatalyst exhibits an outstanding H₂O₂ production rate of 8160 μmol g⁻¹ h⁻¹ in pure water under visible light. In situ spectroscopic characterization combined with DFT calculations demonstrates that synergistic proton–electron transfer facilitates the direct two-electron oxygen reduction pathway. This work underscores the critical role of nanoscale spatial organization of functional groups in modulating PCET kinetics, offering a broadly applicable molecular design strategy for developing high-performance polymer photocatalysts.