טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAtlas Imri
SubjectPeriodic Energy Conversion in an Electric-Double-Layers
Capacitor (EDLC)-Based Transducer
DepartmentDepartment of Energy
Supervisor Assistant Professor Guy Ramon


Abstract

Electrostatic conversion devices operate through modulation of capacitance. Such devices have a wide range of configurations, mostly involving either changes in dielectric permittivity, electrode-plate spacing or over-lapping area. An electric-double-layer capacitor (ELDC) stores electric energy within an interfacial structure formed in an electrolyte adjacent to electrodes, known as the electric double layer (EDL).

The presented study examines, theoretically, an electric-double-layer capacitor (EDLC)-based transducer, as it converts periodic salt and heat fluxes into an electric alternating current. In general, a constant voltage applied at EDLC electrodes forms two opposite sign diffusive EDL’s. An electric current is generated when ionic charges pass from one EDL to the other. In the examined configuration, this ionic charge transfer is induced by boundary modulation of either an electrically-neutral ion flux or temperature. To capture the oscillating dynamics of the ion distribution and ion flux, we solve the full set of Poisson-Nernst-Planck equations coupled with the energy equation, with the appropriate oscillating boundary conditions.

We find that the transducer’s optimal performance conditions, where the maximal current density amplitude is attained, is found to be governed by three main factors: geometric confinement - where the capacitor thickness is on the order of the EDL’s characteristic Debye screening length, the resonant frequency - dictated by characteristic heat and mass diffusion time-scales, and, finally, the extant of losses due to electrostatic work and Joule heating induced by ionic charge diffusion and electro migration.