Microdroplets Boosted Photocatalytic H₂O₂ Production Over Covalent Organic Frameworks via Tri-Phase Interface...

Photocatalytic H₂O₂ production from H₂O/O₂ 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 H₂O₂ production rate was significantly enhanced. The yield strongly depends on droplet size. At 1 µL under air atmosphere, H₂O₂ yield reached 11.11 mmol g^-1 h^-1, representing a 12.3-fold increase over bulk water systems. Under O₂, the yield increases to 14.79 mmol g^-1 h^-1, outperforming most reported photocatalysts. The large specific surface area of microdroplets enhances O₂ 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 O₂ adsorption behavior is modulated by the substrate, which regulates O₂ 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 H₂O₂ generation.