Strongly nonlinear dynamics of electrolytes in large ac voltages
Name
Olesen-2010-Strongly nonlinear d.pdf
Size
1.02 MB
Format
Adobe PDF
Checksum (MD5)
ab5bfc8032a8cc5292b5791b41e9eb50
Author(s)
Hojgaard Olesen, Laurits
Bazant, Martin Z.
Bruus, Henrik
Date Issued
July 2010
Journal
Physical Review E
Publisher
American Physical Society
Citation
Hojgaard Olesen, Laurits, Martin Z. Bazant, and Henrik Bruus, "Strongly nonlinear dynamics of electrolytes in large ac voltages." Physical Review E 82.1 (2010) : 011501. © 2010 The American Physical Society
Version
Final published version
Abstract
We study the response of a model microelectrochemical cell to a large ac voltage of frequency comparable to the inverse cell relaxation time. To bring out the basic physics, we consider the simplest possible model of a symmetric binary electrolyte confined between parallel-plate blocking electrodes, ignoring any transverse instability or fluid flow. We analyze the resulting one-dimensional problem by matched asymptotic expansions in the limit of thin double layers and extend previous work into the strongly nonlinear regime, which is characterized by two features—significant salt depletion in the electrolyte near the electrodes and, at very large voltage, the breakdown of the quasiequilibrium structure of the double layers. The former leads to the prediction of “ac capacitive desalination” since there is a time-averaged transfer of salt from the bulk to the double layers, via oscillating diffusion layers. The latter is associated with transient diffusion limitation, which drives the formation and collapse of space-charge layers, even in the absence of any net Faradaic current through the cell. We also predict that steric effects of finite ion sizes (going beyond dilute-solution theory) act to suppress the strongly nonlinear regime in the limit of concentrated electrolytes, ionic liquids, and molten salts. Beyond the model problem, our reduced equations for thin double layers, based on uniformly valid matched asymptotic expansions, provide a useful mathematical framework to describe additional nonlinear responses to large ac voltages, such as Faradaic reactions, electro-osmotic instabilities, and induced-charge electrokinetic phenomena.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1103/PhysRevE.82.011501
