Significant Acceleration of Photocatalytic CO2 Reduction at the Gas‐Liquid Interface of Microdroplets**

Solar-driven CO2 reduction reaction (CO2 RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO2 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 WO3 ⋅ 0.33H2 O mediated by microdroplets reaches 2536 μmol h-1 g-1 (vs. 13 μmol h-1 g-1 in bulk phase), which is significantly superior to the previously reported photocatalytic CO2 RR in bulk phase reaction condition. Beyond the efficient delivery of CO2 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 CO2 reduction to fuel.