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Related Experiment Video

Updated: Jun 20, 2025

Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone

Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone

Published on: February 23, 2017

Forbidden ion transport through cation exchange membranes.

Chandan K Chaudhary¹, Purnendu K Dasgupta¹

¹Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, TX, 76019-0065, USA.

|July 20, 2024

Summary

Forbidden Ion Transport (FIT) in cation exchange membranes (CEMs) is influenced by membrane properties. High water content, not just ion exchange capacity (IEC), significantly impacts FIT, especially for strong acids transported as molecular acids.

Keywords:

Forbidden ion transport Helfferich model Ion exchange capacity Molecular acids Water sorption

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Area of Science:

Polymer science and engineering
Electrochemistry
Analytical chemistry

Background:

Cation exchange membranes (CEMs) utilize fixed anionic groups to selectively allow cation passage.
Anion passage (Forbidden Ion Transport, FIT) is typically restricted by electrostatic repulsion (Donnan barrier).
Factors governing FIT, beyond concentrated salt solutions, are less understood, impacting applications like electrodialysis and suppressed ion chromatography.

Purpose of the Study:

To investigate the factors controlling Forbidden Ion Transport (FIT) in cation exchange membranes (CEMs).
To explore the relationship between membrane properties (IEC, water content) and FIT.
To understand the transport mechanism of strong acids through CEMs.

Main Methods:

Synthesized a novel ion exchange polymer for microscale applications.
Measured FIT and membrane properties (IEC, water content) for 13 commercial and 4 custom CEMs.
Analyzed the transport of strong acids through CEMs, considering molecular acid activity.

Main Results:

FIT is linearly related to 1/IEC for many CEMs.
For high water-content membranes, water content is a dominant factor in FIT.
Strong acids can be transported through CEMs as un-ionized molecular acids, correlating with their expected activity.

Conclusions:

Membrane water content is a critical, often overlooked, factor in controlling FIT in CEMs.
The transport of strong acids through CEMs occurs significantly via un-ionized molecular species.
Understanding FIT is crucial for optimizing CEM performance in various applications, including ion chromatography and separations.