Highly efficient photocatalytic H2O2 production in microdroplets: accelerated charge separation and transfer at interfaces

Abstract

Solar-driven H₂O₂ production is a promising approach for addressing both the energy and environmental crises. However, H₂O₂ photosynthesis is still restricted by insufficient electron–hole separation efficiency (η_sep) and sluggish semiconductor/solution interface charge transfer efficiency (η_trans). Here, we found that microdroplet photocatalysis showed an ultrahigh H₂O₂ evolution rate (20.6 mmol g_cat⁻¹ h⁻¹) and performance enhancement of two orders of magnitude compared to the corresponding bulk phase counterpart. Microdroplet size effects and in situ Raman measurements on individual microdroplets demonstrated the faster photocatalytic reaction rates in smaller microdroplets and at microdroplet air–water interfaces (AWIs). Besides the sufficient O₂ availability, vibrational Stark effect measurements and DFT calculations revealed that the ultra-strong electric field and partial solvation at microdroplet AWIs could improve η_sep and η_trans, synergistically leading to significant H₂O₂ photosynthesis acceleration. As a proof-of-concept, the in situ applicability of microdroplet H₂O₂ photosynthesis was demonstrated. This study highlights the prospects of microdroplets for accelerating semiconductor photocatalysis.