Microdroplet Interfacial Electric Field Triggers Hydroxyl Radical Coupling Toward Efficient H 2 O 2 Photosynthesis

ABSTRACT The two‐electron water oxidation reaction (2e − WOR) via ·OH coupling offers a direct route for H 2 O 2 photosynthesis, but conventional bulk systems remain rigidly limited by high thermodynamic barriers, short‐lived ·OH, and disordered H‐bond networks. Inspired by the potential of reaction microenvironments to drive thermodynamically unfavorable pathways, we developed a microdroplet photocatalytic platform using hydrophilic nitrogen‐rich COFs (Tp‐DAPd and Tp‐DAPm), achieving H 2 O 2 photosynthesis rates of 11.12 and 12.15 mmol·L −1 ·g −1 , with 11.6‐ and 7.9‐fold enhancements over their bulk counterparts, respectively. Product‐labeling fluorescence imaging microscopy (PLFIM) at the single‐microdroplet scale visualized size‐dependent acceleration and inward expansion of the interfacial reactive zone. Multiscale mechanistic investigations reveal that the intrinsic microdroplet interfacial electric field actively regulates the 2e − WOR process by restructuring the H‐bond network into a low‐entropy state, stabilizing partially solvated ·OH, and inducing a favorable trans‐gauche configuration. These effects work together to create a unique microenvironment that promotes water dissociation and ·OH coupling, thereby lowering the thermodynamic barrier for 2e − WOR under operational conditions. This work represents a microenvironment‐oriented strategy to overcome intrinsic thermodynamic limitations and inspires new strategies for the rational design of microdroplet‐assisted photosynthetic systems.