Reverse Electrowetting-on-Dielectric Energy Harvesting Using 3-D Printed Flexible Electrodes for Self-Powered Wearable Sensors

Reverse electrowetting-on-dielectric (REWOD) presents a unique low-frequency motion energy harvesting method to self-power wearable sensors for human health monitoring in real-time. However, previous studies in REWOD energy harvesting have mainly focused on enhancing power density using rigid electrodes, which due to their rigidity, are not ideal to be implemented as wearable energy harvesting or motion sensing applications from human motion activities. To be considered as the next generation self-powered wearable sensors, self-powered wearable sensors should operate continuously and sustainably in any kind of electrode bending motion and without an external power source. Herein, we demonstrate ac current generation by repeatedly modulating a liquid droplet of microliter volume on an elastomer-based three-dimensional printed flexible electrode without any external bias source. Flexible electrodes were fabricated by deposition of ∼200 nm of titanium (Ti) and an additional ∼200 nm of aluminum oxide (Al
₂
O
₃
) along with ∼50 nm of chromium (Cr) as an interlayer between the metal and the dielectric layers, and all of these on a flexible polydimethylsiloxane substrate. Using a 50 μL electrolyte droplet and 2.5 mm of electrode displacement at a low-frequency motion of 1–2 Hz, a maximum peak-to-peak ac current of ∼340 nA was measured. Although significant progress has yet to be made toward implementing REWOD energy harvesting as a reliable source of power for wearable self-powered systems, this letter signifies the proof-of-concept in implementing flexible electrodes in REWOD energy harvesting.