Enhanced Salt Removal by Unipolar Ion Conduction in Ion Concentration Polarization Desalination
Author(s)Chen, Lan; Kwak, Rhokyun; Pham, Van-Sang; Kim, Bumjoo; Han, Jongyoon
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Chloride ion, the majority salt in nature, is ∼52% faster than sodium ion (D[subscript Na+] = 1.33, D[subscript Cl−] = 2.03[10[superscript −9]m[superscript 2]s[superscript −1]]). Yet, current electrochemical desalination technologies (e.g. electrodialysis) rely on bipolar ion conduction, removing one pair of the cation and the anion simultaneously. Here, we demonstrate that novel ion concentration polarization desalination can enhance salt removal under a given current by implementing unipolar ion conduction: conducting only cations (or anions) with the unipolar ion exchange membrane stack. Combining theoretical analysis, experiment, and numerical modeling, we elucidate that this enhanced salt removal can shift current utilization (ratio between desalted ions and ions conducted through electrodes) and corresponding energy efficiency by the factor ∼(D[subscript −] − D[subscript +])/(D[subscript −] + D[subscript +]). Specifically for desalting NaCl, this enhancement of unipolar cation conduction saves power consumption by ∼50% in overlimiting regime, compared with conventional electrodialysis. Recognizing and utilizing differences between unipolar and bipolar ion conductions have significant implications not only on electromembrane desalination, but also energy harvesting applications (e.g. reverse electrodialysis).
DepartmentMassachusetts Institute of Technology. Department of Biological Engineering; Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science; Massachusetts Institute of Technology. Department of Mechanical Engineering; Massachusetts Institute of Technology. Research Laboratory of Electronics
Kwak, Rhokyun, Van Sang Pham, Bumjoo Kim, Lan Chen, and Jongyoon Han. “Enhanced Salt Removal by Unipolar Ion Conduction in Ion Concentration Polarization Desalination.” Scientific Reports 6 (May 9, 2016): 25349.
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