Optimizing Oxygen and Water Affinity in Aliphatic Acylhydrazone Covalent Organic Frameworks for Efficient H2O2 Photosynthesis from Water and Air
Photocatalytic production of hydrogen peroxide (H2O2) via oxygen reduction reaction (ORR) and water oxidation reaction (WOR) from water and air offers a sustainable alternative to conventional anthraquinone processes. However, the intrinsic kinetic mismatch—fast ORR (microseconds to milliseconds) versus sluggish WOR (seconds)—limits overall efficiency. Here, we report aliphatic acylhydrazone covalent organic frameworks (AA-COFs) synthesized by coupling aliphatic hydrazides with benzotrithiophene motifs via acylhydrazone linkages. The pore walls are decorated with abundant S, O, and N heteroatoms, enhancing affinity toward both O2 and H2O, thereby improving the kinetics of both half-reactions. Through single-carbon atomic engineering, the optimized AA-COF achieves a trade-off between ORR and WOR kinetics, enabling efficient overall H2O2 photosynthesis from water and air without sacrificial agents. The material exhibits a H2O2 production rate of 4777 μmol g−1 h−1 and an O2 utilization/conversion efficiency of 99.3%. This work demonstrates that rational design of heteroatom-rich COFs can synchronize ORR and WOR, overcoming a major bottleneck in artificial photosynthesis.