Triboelectricity-based self-charging droplet capacitor for harvesting low-level ambient energy

Abstract

Abstract In this study, we propose a self-charging droplet capacitor for harvesting low-level mechanical energy. The capacitor comprises of a conductive liquid droplet, which is placed on a heterogeneous and hydrophobic surface of dielectric materials coated onto a conductive substrate. The substrate and the droplet, along with the dielectric materials in between, form a parallel-plate type capacitor. The droplet is free to move on the surface, and thus, enables the position-dependent variation of capacitance. The surface consists of two regions, each with a different material and thickness. The different strengths of solid-water contact electrification of the two materials give rise to a self-charging mechanism. The variation in thickness allows for the capacitance change required for energy harvesting. A device is fabricated with two droplet capacitors and one ceramic capacitor. Passive diode switches are used to enable reconfiguration of the connectivity of the capacitors, which leads to a geometrical growth of the energy in the system. With a 450 μL water drop in each capacitor, the device can effectively harvest energy from low ambient vibrations. The energy harvested grows by 100 times within 11 cycles, sufficient to illuminate 30 LEDs connected in series.