Microstructure Determines Water and Salt Permeation in Commercial Ion-Exchange Membranes

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Ion-exchange membrane (IEM) performance is crucial for energy efficiency in electrochemical devices like fuel cells and batteries.
• Water and co-ion transport significantly impact energy efficiency by causing uncontrolled mixing, especially in applications like reverse electrodialysis (RED).
• Limited quantitative data on water and salt permeability hinders optimal IEM selection for various applications.

Purpose of the Study:

• To quantify water and salt transport properties of 20 commercial IEMs.
• To analyze the relationship between permeability, diffusion, and partitioning using the solution-diffusion model.
• To identify key factors influencing IEM performance in electrochemical processes.

Main Methods:

• Measured water and salt transport properties (permeance, diffusion, partitioning) for 20 commercial IEMs.
• Applied the solution-diffusion model to analyze transport mechanisms.
• Correlated transport properties with membrane characteristics.

Main Results:

• Water and salt permeance varied over several orders of magnitude among the tested IEMs.
• Water and salt diffusion coefficients were identified as the primary drivers of permeance differences.
• A strong positive correlation was observed between water and salt permeability across all IEMs, irrespective of polymer type or reinforcement.

Conclusions:

• IEMs exhibit a wide range of water and salt transport characteristics, influencing their suitability for specific electrochemical applications.
• Membrane microstructure, rather than polymer-chain interactions, governs mobile salt transport in highly swollen IEMs.
• Understanding these transport properties is essential for designing and selecting efficient IEMs for energy conversion and storage technologies.