Modulating Covalent Organic Framework Nanochannel Microenvironments for Sustainable Hydrogen Peroxide Photosynthesis

Photocatalytic hydrogen peroxide (H 2 O 2 ) synthesis from water and oxygen is a promising alternative to the anthraquinone process, but its efficiency depends on charge separation and reactant transport. Herein, we report a side chain strategy to regulate nanochannel microenvironments of hydrazone‐linked covalent organic frameworks (COFs). Four COFs bearing H, OMe, OEt, or OEtOMe groups were prepared using the same benzotrithiophene node and hydrazone‐linked framework. The alkoxy side chains tune pore polarity, accessible porosity, electronic properties, and water and oxygen adsorption. Among them, COF‐Hz‐OEtOMe exhibits the strongest water and oxygen affinity and favorable charge‐separation behavior. It achieves an H 2 O 2 production rate of 7240 µmol g −1 h −1 at the optimized catalyst loading in pure water and 22910 µmol g −1 h −1 with benzyl alcohol. A 1 L reactor using tap water and air accumulates 1.42 mM H 2 O 2 after 4 h under natural sunlight. Experiments and theoretical calculations suggest that the conjugated framework promotes charge separation, while the alkoxy‐functionalized nanochannels improve reactant adsorption and oxygen activation. Life cycle assessment (LCA) highlights that natural sunlight and larger‐scale catalyst synthesis can reduce the calculated climate impact. These results demonstrate that pore‐wall side chain engineering provides an effective strategy for regulating charge behavior and reactant transport in porous photocatalysts.