Solar-driven H2O2 production is a promising approach for addressing both the energy and environmental crises. However, H2O2 photosynthesis is still restricted by the insufficient electron-hole separation efficiency (ηsep) and sluggish...

Solar-driven CO 2 reduction reaction (CO 2 RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO 2 RR efficiency at the abundant gas-liquid interface provided by microdroplets is two orders of magnitude higher than that of the corresponding bulk phase reaction. Even in the absence of sacrificial agents, the production rates of HCOOH over WO 3 • 0.33H 2 O mediated by microdroplets reaches 2536 μmol h À 1 g À 1 (vs. 13 μmol h À 1 g À 1 in bulk phase), which is significantly superior to the previously reported photocatalytic CO 2 RR in bulk phase reaction condition. Beyond the efficient delivery of CO 2 to photocatalyst surfaces within microdroplets, we reveal that the strong electric field at the gas-liquid interface of microdroplets essentially promotes the separation of photogenerated electron-hole pairs. This study provides a deep understanding of ultrafast reaction kinetics promoted by the gas-liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO 2 reduction to fuel.

Fe(III)–oxalate complexes are ubiquitous in atmospheric environments, which can release reactive oxygen species (ROS) such as H2O2, O•2–, and OH• under light irradiation. Although Fe(III)–oxalate photochemistry has been investigated extensively, the understanding of its involvement in authentic atmospheric environments such as aerosol droplets is far from enough, since the current available knowledge has mainly been obtained in bulk-phase studies. Here, we find that the production of OH• by Fe(III)–oxalate in aerosol microdroplets is about 10-fold greater than that of its bulk-phase counterpart. In addition, in the presence of Fe(III)–oxalate complexes, the rate of photo-oxidation from SO2 to sulfate in microdroplets was about 19-fold faster than that in the bulk phase. The availability of efficient reactants and mass transfer due to droplet effects made dominant contributions to the accelerated OH• and SO4 2– formation. This work highlights the necessary consideration of droplet effects in atmospheric laboratory studies and model simulations.

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