Acidic modulation of CO2 fixation by pyruvate in micron-sized water microdroplets

Water microdroplets possess energetic interfaces that can promote the reduction and utilization of carbon dioxide (CO 2 ). However, the mechanism by which acidity modulates CO 2 interfacial reactions in microdroplets remains unclear. Herein, CO 2 fixation in pyruvate-containing microdroplets was investigated over a pH range of 1.5–10.1. Online mass spectrometry showed that acidic conditions significantly enhance the reaction between CO 2 and pyruvate, particularly in smaller droplets and at lower pyruvate concentrations. A similar promotion was observed for another α-keto acid, α-ketoglutaric acid. Mechanistic analysis suggests that electrostatic attraction between interfacial anions (Cl - and OH - ) and protons amplifies the interfacial electric field at the air-water interface, which drives CO 2 fixation rather than conventional proton catalysis. These findings highlight the critical role of acidity in interfacial CO 2 -related chemistry and may help improve the understanding of environmentally relevant microdroplet carbon processes.