Cumulative charging behavior of water droplet driven freestanding triboelectric nanogenerators toward hydrodynamic energy harvesting

Abstract

Triboelectric nanogenerators (TENGs) have received growing attention to efficiently harvest waste micromechanical energy from ambient atmosphere such as hydrodynamic energy from raindrops. The comprehensive understanding of the electrification mechanism and dynamic charging behavior between rain droplets and the collecting substrate is essential for multi-application scenarios of TENGs. Herein, a bi-electrode freestanding mode TENG (BF-TENG) is designed to harvest hydrodynamic energy from rain droplets with regard to the implementation at rooftops, terraces and greenhouse roofs. By placing the BF-TENG horizontally, an intriguing cumulative charging behavior of successive water droplets is in-depth investigated, which expands the fundamental charging mechanism for maximizing the surface charge storage capacity. Optimal configurations of the inclination angle and drop height of the BF-TENG system are further studied for improving the electrification charge density as well as power output and extending the application area to inclined surfaces such as rooftops and umbrellas. Through coupling of the cumulative charging behavior and the optimal configurations of BF-TENG, an instantaneous maximum power density of 1.838 W m⁻² is achieved and 30 LEDs can be lit up when spraying tap water from a shower faucet on a BF-TENG installed on an umbrella, demonstrating the promising application of BF-TENGs for hydrodynamic energy harvesting and providing multi-implementation scenarios of BF-TENGs with the potential to be installed on the roof top, terrace, umbrella and car hood, which can be utilized as the warning light at rainy night for safe guarding.