Water-solid contact electrification causes hydrogen peroxide production from hydroxyl radical recombination in sprayed microdroplets.

Contact electrification between water and a solid surface is crucial for physicochemical processes at water-solid interfaces. However, the nature of the involved processes remains poorly understood, especially in the initial stage of the interface formation. Here we report that H ₂ O ₂ is spontaneously produced from the hydroxyl groups on the solid surface when contact occurred. The density of hydroxyl groups affects the H ₂ O ₂ yield. The participation of hydroxyl groups in H ₂ O ₂ generation is confirmed by mass spectrometric detection of ¹⁸ O in the product of the reaction between 4-carboxyphenylboronic acid and ¹⁸ O-labeled H ₂ O ₂ resulting from ¹⁸ O ₂ plasma treatment of the surface. We propose a model for H ₂ O ₂ generation based on recombination of the hydroxyl radicals produced from the surface hydroxyl groups in the water-solid contact process. Our observations show that the spontaneous generation of H ₂ O ₂ is universal on the surfaces of soil and atmospheric fine particles in a humid environment.