Charged Water Microdroplets Enable Dissociation of Surrounding Dioxygen

Abstract

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.