Liquid-solid contact electrification when water droplets hit living plant leaves

Contact electrification has gained interest as a mechanism for generating charges on surfaces. It has also been shown that plant leaves generate electrification by both solid-solid and liquid-solid contact. However, it is unclear how water droplets hitting a leaf causes charging and which structural features affect this phenomenon. Here, we show how the in-situ surface structures of leaves, droplet composition, and prior ionization of the droplet influence living plant liquid-solid contact electrification on several superhydrophobic and hydrophilic living plant species. We find that the hierarchical structures responsible for self-cleaning and wetting, known as the Lotus effect, also create a specific electrification pattern. Each water droplet causes a characteristic signal in the plant tissue depending on the structure and composition of the epicuticular wax layer as well as the droplet composition. These findings give insight on how contact electrification occurs in nature, suggesting the potential for deriving new bio-based materials for sensing and energy harvesting in artificial and plant-hybrid devices.