Microdroplets Boosted Photocatalytic H ₂ O ₂ Production Over Covalent Organic Frameworks via Tri‐Phase Interface Catalysis

ABSTRACT Photocatalytic H 2 O 2 production from H 2 O/O 2 is a green solar energy conversion strategy, but the conventional bulk liquid systems suffer from poor mass transfer and limited active site accessibility. Here, by introducing sessile water microdroplets into the system using a covalent organic framework (DS‐OH‐COF) as a photocatalyst, the H 2 O 2 production rate was significantly enhanced. The yield strongly depends on droplet size. At 1 µL under air atmosphere, H 2 O 2 yield reached 11.11 mmol g −1 h −1 , representing a 12.3‐fold increase over bulk water systems. Under O 2 , the yield increases to 14.79 mmol g −1 h −1 , outperforming most reported photocatalysts. The large specific surface area of microdroplets enhances O 2 mass transfer into the liquid phase, promoting interaction with catalyst active sites. Most importantly, the gas‐liquid‐solid tri‐phase interface plays a vital role in the catalytic process. Density functional theory calculations confirm that the O 2 adsorption behavior is modulated by the substrate, which regulates O 2 reduction at the tri‐phase interface. The microdroplet system also enabled efficient methyl orange degradation, demonstrating its practical potential. This microdroplet‐based catalytic path effectively overcomes the inherent limitations of insufficient oxygen mass transfer and low efficiency in bulk reactions, providing new insights for catalytic H 2 O 2 generation.