Synergizing Mass Transfer and Exciton Dissociation in Nanoscale COFs for Efficient H2O2 Photosynthesis.

Covalent organic frameworks (COFs) are promising photocatalysts for solar H2O2 production, but their efficiencies remain insufficient for practical application. A primary limitation stems from the coupled proton-electron transfer in the two-electron oxygen reduction reaction (2e- ORR), which demands photoinduced charge generation and rapid proton delivery-features rarely optimized simultaneously in existing COF architectures. Here we address these bottlenecks by combining nanoscale morphological control with pore-wall functionalization. Bottom-up colloidal synthesis produces highly crystalline COF nanospheres that reduce exciton-diffusion losses and enhance light harvesting and charge generation versus bulk COFs. Meanwhile, carboxylic acid groups incorporated into 1D nanopores tune the microenvironment to promote proton delivery. This unified design delivers an exceptional H2O2 evolution rate of 11246 µmol g-1 h-1 (>sevenfold enhancement over pristine bulk COF), and a solar-to-chemical conversion efficiency of 2.18% in pure water under air (AM 1.5G, 100 mW cm-2), among the highest reported for COF-based photocatalysts. Experimental investigations and theoretical calculations reveal the carboxylated pore walls template continuous, oriented hydrogen-bond chains in confined water, lowering the kinetic barrier for the 2e- ORR pathway. This work establishes a generalizable paradigm for orchestrating coupled proton-electron transfer in porous photocatalysts for efficient solar energy conversion.