Unexpected Spontaneous Generation of Superoxide Radicals: Water‐Solid Collision as an Atypical Source

Abstract Spontaneous generation of reactive oxygen species (ROS) driven by water‐solid contact electrification was a new source of redox chemistry. However, superoxide radicals (O 2 •− ), a kind of ROS that was of great significance in both natural and engineering environments, remain overlooked and poorly understood at the water‐solid interface. Here, we found O 2 •− could be generated spontaneously when water collided with the solid interface even under dark conditions, and its production was quantified by CL. 18 O isotope labelling experiments and solid–liquid contact electrification detection confirmed that the generation of O 2 •− was from the reduction of dissolved oxygen by electrons at the water‐solid interface and that the kinetic energy of the water energized the reaction. Given the ubiquitous nature of solid–liquid collisions, such as rain colliding with mineral surfaces during rainfall, we further systematically investigated the O 2 •− generation and their decay kinetics at three distinct rain‐mineral interfaces. Results showed that O 2 •− generation ranged from 0.015 to 1.1 nM, comparable to the O 2 •− production by photochemical pathways. Our findings established the water‐solid collision interface as a previously unrecognized global source of O 2 •− and highlight a universal yet overlooked physicochemical mechanism underpinning multiphase redox chemistry.