Droplet Electricity Harvesting: From Liquid-Solid Interface to Energy-per-Droplet

The growing demand for energy, along with the environmental and economic challenges associated with fossil fuel consumption, has created an urgent need for renewable energy sources. Water-based sources are considered a potential source of renewable energy because about 71% of the Earth’s surface is covered by water. With advances in droplet-based triboelectric nanogenerators and droplet electricity generators, and the ubiquity of water, energy harvesting using droplet-based systems has become a promising method for capturing ambient mechanical energy with straightforward device designs. To better understand droplet electricity harvesting, this review summarizes the fundamental mechanisms of droplet-induced electricity generation, discusses the performance metrics needed for reliable device comparison, and highlights major strategies for improving output and efficiency. Representative applications of these systems and assess the principal challenges that currently limit their practical implementation are further examined. By elucidating the connections among mechanisms, performance, and applications, this review provides a framework for the continued advancement of droplet-based electricity-harvesting technologies.