Building-block exchange enables synergistic regulation in covalent organic frameworks for photocatalytic H2O2 production

Engineering covalent organic frameworks (COFs) for photocatalytic H 2 O 2 synthesis is often constrained by the intrinsic coupling of band energetics, charge utilization, and surface microenvironment. Here we introduce a surface-directed building-block exchange strategy that selectively reprograms the outer/near-surface domains of imine-linked COFs while largely preserving crystallinity and pore architecture, enabling coordinated yet decoupled regulation of electronic structure and interface chemistry within a single scaffold. Across a sequential exchange series, we experimentally demonstrate that no single structural descriptor, such as donor–acceptor strength or bandgap, can reliably predict photocatalytic performance. Instead, high H 2 O 2 productivity requires the concerted optimization of conduction-band positioning, charge separation/transport, and interfacial properties. The optimized N/Trz-Bz-COF exhibits a substantially more negative conduction band and enhanced charge-carrier utilization, delivering an H 2 O 2 production rate of 11034 μmol·g⁻¹ ·h⁻¹ . Spin-trapping EPR, scavenger tests, and in-situ DRIFTS identify ·O₂⁻/·OOH as key intermediates, supporting a predominant 2e⁻ ORR pathway. This work establishes surface building-block exchange as a general post-synthetic lever for integrating band modulation, charge management, and microenvironment engineering toward efficient H 2 O 2 photosynthesis.