Liquid Droplet–Based Triboelectric Nanogenerator

The tiny liquid droplet is a big treasure of energy. When falling from the sky as precipitation, a water droplet will gradually accelerate and gain a huge amount of kinetic energy. Meanwhile, the falling droplet will also accumulate electrostatic energy due to the contact electrification between water droplet and air, which is also the main cause of thunderstorms. Given the estimation of approximately 5 × 105 km3 of rainfall per year all over the world, the water droplets entreasure a huge amount of energy of 3000 TW h per year. However, such low-frequency and discrete droplet energies are difficult to be scavenged by widely used conventional hydraulic technology that is designed for harvesting energy from high-frequency water flow. Recently, featuring low cost, ease of fabrication, high-energy conversion efficiency, and high instantaneous power density, triboelectric nanogenerators (TENGs) can enable an efficient conversion from droplet energy to electricity by leveraging the coupling of contact electrification and electrostatic induction, offering an attractive and promising platform for developing effective droplet energy harvesting technologies.