Significant Acceleration of Photocatalytic CO2 Reduction to HCOOH at Gas-Liquid Interface

Abstract Solar‐driven CO2 reduction reaction (CO2RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalysis CO2RR 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 rate of HCOOH over WO3·0.33H2O mediated by microdroplets reaches 2536.23 μmol h-1g-1 (vs. 13.32 μmol h-1g-1 in bulk phase), which is significantly superior to the previously reported photocatalysis CO2RR in bulk phase water. 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. A scalable HCOOH photocatalysis production is further demonstrated by using an electric nebulizer to generate a large number of microdroplets. This study provides a deep understanding of ultrafast reaction kinetics mediated by the gas-liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO2 reduction.