Theoretical demonstration of a capacitive rotor for generation of alternating current from mechanical motion

Abstract

Innovative concepts and materials are enabling energy harvesters for slower motion, particularly for personal wearables or portable small-scale applications, hence contributing to a future sustainable economy. Here we propose a principle for a capacitive rotor device and analyze its operation. This device is based on a rotor containing many capacitors in parallel. The rotation of the rotor causes periodic capacitance changes and, when connected to a reservoir-of-charge capacitor, induces alternating current. The properties of this device depend on the lubricating liquid situated between the capacitor’s electrodes, be it a highly polar liquid, organic electrolyte, or ionic liquid – we consider all these scenarios. An advantage of the capacitive rotor is its scalability. Such a lightweight device, weighing tens of grams, can be implemented in a shoe sole, generating a significant power output of the order of Watts. Scaled up, such systems can be used in portable wind or water turbines.

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

“…Kolomeisky and Kornyshev suggested an alternative approach based on the reversible penetration of a liquid electrolyte into a solvophobic porous electrode, which could be used in a “double layer shoe” to harvest electricity from walking motion . Analogous to the use of moving wire electrodes in CDI for desalination, capacitive rotors have been proposed to generate alternating current from mechanical motion by exploiting a time-varying EDL capacitance …”

Ionotronics for reverse actuation

“…If the film thickness is smaller than this (we will not encounter this situation), the capacitance also increases as it reaches the limit of the capacitance of the ultra-thin film dielectric capacitor (see supplementary information of ref. 26).…”

“…To save on battery life, we note that the constant use of the battery is optional, as one can replace it with another pre-charged capacitor characterised by a much larger and constant capacitance, as shown in ref. 26. Such replacement will not affect the basic equations describing the operation of this system.…”

“…The capacitance value, C , is set by the product of capacitance per unit area, C s , and the area of the capacitor, S . A change in capacitance can be achieved by varying the capacitance per unit-area, 26 or the effective surface area of the electrode/electrolyte interface. In this paper we consider only the latter case.…”

“…In the above examples, capacitance was varied by squeezing liquid droplets to change their contact area with electrodes. In more recent examples, capacitance was varied instead by changing the area of submersion of the electrodes in an electrolyte, 12 or sliding 25 or rotating 26 electrodes relative to each other. There are also other ionotronic harvesters, which utilise different types of energy, such as osmotic power – the so-called blue energy.…”