Simultaneous generation of hydroxyl and hydrogen radicals from H+/OH− pairs caused by water–solid contact electrification

Water–solid contact electrification is a common physical phenomenon involving interfacial electron and ion transfer, recently discovered to trigger unique redox reactions. Here, we demonstrate the generation of both hydroxyl and hydrogen radicals when water contacts SiO₂. The coexistence of hydroxyl and hydrogen radicals is confirmed by simultaneous nitrate reduction and nitrite oxidation during the contact. Increased density of hydroxyl groups on the SiO₂ surface enhances its surface electronegativity before the contact, as well as boosting charge transfer and radical generation during the contact. We propose that the simultaneous generation of hydroxyl and hydrogen radicals originates from electron gain and loss between hydroxide anions in water and hydrogen cations adsorbed on the solid surface, which are ion pairs separated by the interfacial electric field. This discovery advances our understanding of redox processes induced by contact electrification.