Reverse electrowetting as a new approach to high-power energy harvesting

Over the last decade electrical batteries have emerged as a critical bottleneck for portable electronics development. High-power mechanical energy harvesting can potentially provide a valuable alternative to the use of batteries, but, until now, a suitable mechanical-to-electrical energy conversion technology did not exist. Here we describe a novel mechanical-to-electrical energy conversion method based on the reverse electrowetting phenomenon. Electrical energy generation is achieved through the interaction of arrays of moving microscopic liquid droplets with novel nanometer-thick multilayer dielectric films. Advantages of this process include the production of high power densities, up to 103 W m−2; the ability to directly utilize a very broad range of mechanical forces and displacements; and the ability to directly output a broad range of currents and voltages, from several volts to tens of volts. These advantages make this method uniquely suited for high-power energy harvesting from a wide variety of environmental mechanical energy sources

Electrically controlled localized charge trapping at amorphous fluoropolymer-electrolyte interfaces

Charge trapping is a long-standing problem in electrowetting-on-dielectric (EWOD), causing reliability reduction and restricting its practical applications. Although this phenomenon has been investigated macroscopically, the microscopic investigations are still lacking. In this work, the trapped charges are proven to be localized at three-phase contact line region by using three detecting methods -- local contact angle measurements, electrowetting (EW) probe, and Kelvin Probe Force Microscopy (KPFM). Moreover, we demonstrate that this EW-induced charge trapping phenomenon can be utilized as a simple and low-cost method to deposit charges on fluoropolymer surfaces. Charge density near the three-phase contact line up to 0.46 mC/m2 and the line width with deposited charges ranging from 20 to 300 micrometer are achieved by the proposed method. Particularly, negative charge densities do not degrade even after harsh testing with a water droplet on top of the sample surfaces for 12 hours, as well as after being treated by water vapor for 3 hours. These findings provide an approach for applications which desire stable and controllable surface charges

Electric generation from drops impacting onto charged surfaces

The impact of liquid drops onto solid surfaces leads to conversion of kinetic energy of directed drop motion into various forms of energy including surface energy, vibrational energy, heat, and under suitable conditions, electrical energy. The latter has attracted substantial attention in recent years for its potential to directly convert energy from random environmental flows such as rainfall, spray, and wave motion on the sea to electrical energy. Despite the invention of numerous configurations of such energy harvesters, the underlying physical principles and optimum operation conditions have remained elusive. In this letter, we use a combination of high-speed electrical current and video imaging measurements to develop a parameter-free quantitative description of the energy harvesting process for an optimized electrode configuration. A novel electrowetting-assisted charge injection method, EWCI, enables highly stable surface charges and robust energy conversion for several months with record efficiencies exceeding 2.5 percent of the initial kinetic energy

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

Article presents 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

Characterization of advanced materials for low-frequency Vibrational Energy Harvesting (VEH)

openNowadays sensors are among the most exploited systems in everyday life, with several applications stimulating an increasing amount of research. They generally require external power, thus adding issues such as maintenance and size constraints. The most promising energy harvesting (EH) technology for miniaturization is Reverse Electro wetting on Dielectric (REWoD). It can provide high power density by exploiting the mechanical modulation of the capacity at the liquid/dielectric interface attaining, without any external bias, power densities of µW/cm2. With respect to other EH techniques, REWoD harvests energy from low frequency vibrations (< 10Hz, human motion). I exploited low-cost materials as proof of concept of the feasibility of vibrational EH, suitable for wearable devices, using highly hydrophobic Al and PVDF coated electrodes in combination with polyacrylamide (PAAm) hydrogels loaded with LiCl solutions. The morphology at the sub-micrometer scale and the composition of the outer layers of Al have been studied as a function of the chemical etching time and have been correlated with the surface wettability. The etched Al surfaces exhibit binary structures with nanoscale block-like convexes and hollows, providing more space for air trapping. The analysis shows not only that the change in wetting behaviour correlates with the amount of Al hydroxide at the surface, but also confirms the essential role of the adsorption of airborne carbon compounds. The hydrophobic behaviour depends therefore on the combined effects of surface morphology and surface chemical composition. To compensate for the degradation of the hydrogels with time due to the microstructure of the external oxide layer, an alternative bare Al electrode covered with PVDF has been tested: PAAm hydrogels show now no degradation with time while being able to provide, at frequencies lower than 10 Hz, a peak power/unity of 0.6 Watt, higher than 0.25 Watt, obtained by using the Al oxide electrode.openXXXIII CICLO - SCIENZE E TECNOLOGIE DELLA CHIMICA E DEI MATERIALI - Scienza e tecnologia dei materialiPaolini, Giuli

Energy Harvesting Through Reverse Electrowetting

Over the last decade electrical batteries have emerged as a critical bottleneck for portable electronics development. High-power mechanical energy harvesting can potentially provide a valuable alternative to the use of batteries, but, until now, a suitable mechanical-to-electrical energy conversion technology did not exist. Here we describe a novel mechanical-to-electrical energy conversion method based on the reverse electrowetting phenomenon. Reverse electrowetting has emerged as a highly potential method for high power energy harvesting with good environmental coupling. Device simulation using fluid flow model of COMSOL multiphysics has been presented in this thesis. Harvested energy from this kind of device is directly proportional to change in capacitance from wetting to non-wetting condition i.e. the device should have high capacitance per unit volume. It has been found that high K dielectric material offers high capacitance at low operating voltage. Further reduction in operating voltage can be accomplished by decreasing dielectric thickness. However it has been proposed to use 10nm dielectric thickness for ease in fabrication. Finally capacitance of 4.213nF at an operating voltage of 4.9V has been achieved by choosing 10nm of TiO2 ( ) as a dielectric material with the device of radius 100um. Instead of using single big droplet, use of multiple small droplets of same volume offer more capacitance and hence the harvested energy. Apart from this simulation, device fabrication has been done using two different methods, one is based on UV lithography and another is based on X-ray lithography. All the obstacles and problems encountered in this fabrication have been discussed thoroughly in this thesis