Charged Water Microdroplets Enable Dissociation of Surrounding Dioxygen

The cleavage of dioxygen (O₂) into its atomic constituents typically requires harsh conditions and metal catalysts. We present a remarkable discovery demonstrating that dioxygen can be activated, dissociated, and subsequently transformed into the ozone anion (O₃^-) without any catalyst at the air-water interface in charged microdroplet sprays. Using online mass spectrometry, we directly detected the dioxygen splitting products O₃^- and H₂O·O₃^- in microdroplets. The high electric field at the air-water interface, along with microlightning between oppositely charged water microdroplets, induces an electrical discharge responsible for the O-O bond cleavage, leading to the formation of reactive oxygen species (ROS). Isotope labeling experiments further reveal that various ROS, i.e., ·OH, CO₃^-, and HCO₄^-, can be generated through the reaction of dioxygen splitting products with water or CO₂. This study introduces a sustainable pathway for molecular oxygen utilization and offers new insights into ROS generation in microdroplets.