Spontaneously charged water drops induce corrosion.

Water drops spontaneously become electrically charged when moving on different surfaces, such as plant leaves, insect wings, building walls, window glass and plastic1-9. This process, known as contact or sliding electrification, is analogous to tribocharging between solids10-13. The electric potential of water drops charged in this way can exceed 1 kV (refs. 14-16). A vital but as yet unanswered question is whether the charge in water drops causes corrosion. Here we analyse the effect of series of water drops hitting metal surfaces, which are protected by a non-conductive coating. Before hitting the coated metal, the drops acquire a charge spontaneously by sliding over an insulating surface. We demonstrated that these charged drops can cause the coating to break down electrically and lead to corrosion of the metal. As spontaneously charged water drops form naturally, this previously overlooked corrosion mechanism may contribute to the degradation of cultural heritage sites, buildings, ships, cars and other metal components. Our findings can improve anticorrosion strategies and emphasize the need for protective materials capable of resisting charge-induced damage from water drops.