High power density and bias-free reverse electrowetting energy harvesting using surface area enhanced porous electrodes

Abstract

Reverse electrowetting-on-dielectric (REWOD) is a novel energy harvesting technology with a significant advantage over other energy harvesting technologies due to its effective performance at a low-frequency range and not requiring resonance frequency of solid structures. However, REWOD energy harvesting based on planar electrodes has a limited surface area and therefore a lower power output. In this work, we present a novel approach for enhancing power output from a REWOD energy harvester by significantly increasing the total available surface area using perforated silicon wafer electrodes. Without applying any external bias voltage, maximum current and voltage densities per unit planar area were measured to be 3.77 μA/cm 2 and 1.05 V/cm 2 , respectively, for a 38 μm pore-size electrode at 5 Hz modulation frequency. RMS power density output was 4.8 μW/cm 2 , which is ∼23 times higher than that from our prior work on planar electrodes showing the significance of porous electrodes in REWOD energy harvesting. A simple capacitive theoretical model validating experimental results was developed and justified. The novelty of this work lies in the combination of a bias-free approach to REWOD energy harvesting coupled with significant enhancement in electrode surface area per planar area to increase the output power density. • Low frequency (1–5 Hz) motion energy harvesting using high surface area electrodes. • Highest reported REWOD power density (4.8 μW/cm 2 ) without bias voltage. • Experimentally supported capacitive theoretical modeling. • Demonstration of increasing power density with shrinking pore size electrodes. • Power density increased by ∼23 times compared to planar electrodes.