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Counter-ion transport number and membrane potential in working membrane systems
Mette Birch Kristensen1, Anders Bentien1, Michele Tedesco2
1Department of Engineering, Aarhus University, Hangoevej 2, 8200 Aarhus N, Denmark.
Journal of Colloid and Interface Science
|June 18, 2017
Summary
This study introduces a space-charge theory model for ion transport in nanopores, offering optimal conditions for membrane potential experiments and a new method for dynamic membrane conductivity measurement.
Area of Science:
- Electrochemistry
- Materials Science
- Physical Chemistry
Background:
- Understanding ion transport in nanoporous membranes is crucial for electrochemical applications.
- Existing models like Uniform Potential (UP) and Teorell-Meyer-Sievers (TMS) have limitations in describing complex membrane behavior.
- Space-charge effects significantly influence ion dynamics within confined geometries.
Purpose of the Study:
- To develop a comprehensive transport model for fluid and ions in cylindrical nanopores using general space-charge (SC) theory.
- To derive equations for membrane potential and counter-ion transport numbers.
- To propose optimal experimental conditions for membrane potential measurements and introduce a novel dynamic method for determining membrane potential and conductivity.
Main Methods:
- Utilized general space-charge (SC) theory for a combined fluid and ion transport model.
- Assumed ion exchange membranes comprise interconnected cylindrical pores.
- Compared SC theory transport numbers with UP and TMS models under various conditions (zero/non-zero concentration gradient, applied current density).
Main Results:
- Derived equations for membrane potential and counter-ion transport numbers based on SC theory.
- Identified optimal experimental conditions (electrolyte, concentration difference) for membrane potential experiments, linked to volumetric charge density.
- Theoretically described a novel dynamic method for simultaneous measurement of membrane potential and conductivity.
- Presented numerical results as a map of electrical potential difference versus average pore radius and charge density.
Conclusions:
- The SC theory provides a robust framework for analyzing ion transport in nanoporous membranes.
- The proposed dynamic method enables efficient characterization of membrane properties.
- The developed map serves as a valuable tool for designing effective membrane morphologies for specific electrochemical applications, such as reverse electrodialysis.
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