The output improvement of droplet-based nanogenerators through enhanced coupling displacement and conducting currents

The advent of triboelectric nanogenerator (TENG) preludes the high entropy energy harvesting and is gradually applied to droplet energy harvesting. However, the mainstream research concentrates on exploring the solid-liquid contact electrification (CE) and electrostatic induction (EI) processes, ignoring the possibility of charge extraction from water. As a result, the droplet-based nanogenerator (DNG) is limited to small alternating-current (AC) output, which also asks for complex power management. This study reveals that the displacement current is not the sole driving force during the power generation of DNG, and the contribution of the conducting current is equally important. Here, the existence of conducting charge is confirmed by a top-electrode-only DNG, and the charge transfer processes in traditional DNGs are re-examined. Finally, a three-electrode total current DNG is introduced to enhance the coupling of displacement current and conducting current. The charge extraction efficiency is then improved by more than one order of magnitude (charge extraction from single droplet is increased from 1 to 27.3 nC) and retains the direct-current (DC) and high voltage (up to 2315 V) output characteristics.