Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Qiao, Rui

Committee Member

Vahidi , Ardalan

Committee Member

Li , Gang

Abstract

A recent increase in the popularity of EDLCs and AC-EOF has necessitated a deeper understanding of the structure and charging kinetics of electrical double layers (EDLs) at electrode-electrolyte interfaces. Here, the charging kinetics of EDLs in nanoscale EDLCs is studied by a circuit model, a Poisson-Nernst-Planck (PNP) mo del, and molecular dynamics (MD) simulations. The results of the MD simulations demonstrate a linear charging behavior of EDLs near planar electrodes for both aqueous and organic electrolytes at charging below 90% and time larger than tens of picoseconds. Additionally, we will show that the circuit and PNP models are capable of accurately capturing this linearity, as well as the overall charging kinetics. Through PNP and MD simulation, a diffusional process is shown to occur which causes a decrease in the concentration of the bulk solution, yet the linearity of charging, at charging below 90%, is not affected because the flux during the charging process is found to be relatively low. The charging kinetics of a slit nanopore electrode is also studied using MD, and interesting results about the linearity of this process is discussed. Finally, a porous geometry modeled by an exohedral pore with multiple solid cylinders will demonstrate that variations in the surface charge density around the solid cylinders will occur during charging due to interactions between nearby charged cylinders. However, these variations in surface charge density along the circumference of the cylinder will approach zero as the system reaches equilibrium.

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