Thermodynamics of Ion Separation by Electrosorption
Name
Thermodynamics_of_Ion_Separation_by_Electrosorptio.pdf
Description
Accepted version
Size
1.69 MB
Format
Unknown
Checksum (MD5)
44cfb6bc4db1a493c87ff0a415de3f02
Author(s)
Hemmatifar, Ali
Ramachandran, Ashwin
Liu, Kang
Oyarzun, Diego I
Bazant, Martin Z
Santiago, Juan G
Date Issued
2018
Journal
Environmental Science and Technology
Publisher
American Chemical Society (ACS)
Version
Author's final manuscript
Abstract
© 2018 American Chemical Society. We present a simple, top-down approach for the calculation of minimum energy consumption of electrosorptive ion separation using variational form of the (Gibbs) free energy. We focus and expand on the case of electrostatic capacitive deionization (CDI). The theoretical framework is independent of details of the double-layer charge distribution and is applicable to any thermodynamically consistent model, such as the Gouy-Chapman-Stern and modified Donnan models. We demonstrate that, under certain assumptions, the minimum required electric work energy is indeed equivalent to the free energy of separation. Using the theory, we define the thermodynamic efficiency of CDI. We show that the thermodynamic efficiency of current experimental CDI systems is currently very low, around 1% for most existing systems. We applied this knowledge and constructed and operated a CDI cell to show that judicious selection of the materials, geometry, and process parameters can lead to a 9% thermodynamic efficiency and 4.6 kT per removed ion energy cost. This relatively high thermodynamic efficiency is, to our knowledge, by far the highest thermodynamic efficiency ever demonstrated for traditional CDI. We hypothesize that efficiency can be further improved by further reduction of CDI cell series resistances and optimization of operational parameters.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Massachusetts Institute of Technology. Department of Mathematics
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.
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DOI of Published Version
https://doi.org/10.1021/ACS.EST.8B02959
