On the Origin of the Membrane Potential Arising Across Densely Charged Ion Exchange Membranes: How Well Does the Teorell-Meyer-Sievers Theory Work?

Document Type: Research Paper

Authors

1 Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 9, 8911 MA Leeuwarden, The Netherlands

2 Membrane Institute, Kuban State University, 149 Stavropolskaya str., 350040 Krasnodar, Russia

Abstract

A difference in salt concentration in two solutions separated by a membrane leads to an electrical potential difference across the membrane, also without applied current. A literature study is presented on proposed theories for the origin of this membrane potential (ϕm). The most well-known theoretical description is Teorell-Meyer-Sievers (TMS) theory, which we analyze and extend. Experimental data for ϕm were obtained using a cation exchange membrane (CMX, Neosepta) and NaCl solutions (salt concentration from 1 mM to 5 M). Deviations between theory and experiments are observed, especially at larger salt concentration differences across the membrane. At a certain salt concentration ratio, a maximum in ϕm is found, not predicted by the TMS theory. Before the maximum, TMS theory can be used as a good estimate of ϕm though it overestimates the actual value. To improve the theory, various corrections to TMS theory were considered: A) Using ion activities instead of ionic concentration in the external solutions leads to an improved prediction; B) Inhomogeneous distribution of the membrane fixed charge has no effect on ϕm; C) Consideration of stagnant diffusion layers on each side of the membrane can have a large effect on ϕm; D) Reducing the average value of the fixed membrane charge density can also largely affect ϕm; E) Allowing for water transport in the theory has a small effect; F) Considering differences in ionic mobility between co-ions and counterions in the membrane affects ϕm significantly. Modifications C) and F) may help to explain the observed maximum in ϕm.

Graphical Abstract

On the Origin of the Membrane Potential Arising Across Densely Charged Ion Exchange Membranes: How Well Does the Teorell-Meyer-Sievers Theory Work?

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