Water droplet energy harvesting

Harnessing abundant kinetic water energy in diverse forms of river flows, ocean waves, tidal currents, raindrops, and others, is highly attractive to ease the energy crisis and satisfy the demands of scattered sensor network nodes in the Internet of things. Among them, raindrops, widely and ubiquitously distributed in nature and ambient living life, have been extensively explored and regarded as significant renewable energy carriers. Extensive efforts have been made to investigate droplet-based electricity nanogenerators in fundamental mechanism, performance, and applications for achieving sustainable energy demands of the rapidly developing society over the past decade. In this review, we introduce the remarkable progress in this field and discuss the fundamental mechanisms of droplet energy harvesting technology for achieving high-power generation. More significantly, a systematic review of droplet energy harvesting in different two-phase interfaces, including liquid–solid, liquid–liquid, and liquid–gas interfaces, is provided. Finally, this survey reveals that droplet-based electricity generators present vast potential in the power supply. At the same time, several development challenges and prospective solutions are discussed to spur future technological advancements.