Cumulative charging behavior of water droplets driven freestanding triboelectric nanogenerator toward hydrodynamic energy harvesting
Triboelectric nanogenerators (TENGs) have received growing attentions to efficiently harvest waste micromechanical energy from ambient atmosphere such as hydrodynamic energy from raindrops. The comprehensive understanding of electrification mechanism and dynamic charging behavior between rain droplets and the collecting substrate are 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 rooftop, terrace and greenhouse roof. 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 inclination angle and drop height of 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 rooftop and umbrella. Through coupling of the cumulative charging behavior and the optimal configurations of BF-TENG, an instantaneous maximum power density of 1.838 W/m2 is achieved and 30 LEDs can be lighted up when spraying tap water from shower faucet on a BF-TENG installed on an umbrella, demonstrating the promising application of BF-TENG for hydrodynamic energy harvesting and providing multi-implementation scenarios of BF-TENG 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.