Interface Engineering by Molecular Layer Deposition on Polymer Membrane for Selective Ion Transport.

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Engineering

Background:

• Nafion membranes are crucial for ion transport but often lack selectivity.
• Enhancing ion selectivity is key for advanced separation technologies.

Purpose of the Study:

• To investigate molecular layer deposition (MLD) of ethylene glycol-alucone (EG-alucone) on Nafion.
• To understand the impact of EG-alucone MLD on Nafion morphology and ion transport selectivity.

Main Methods:

• X-ray photoelectron spectroscopy (XPS)
• Scanning electron microscopy (SEM)
• Density functional theory (DFT)
• Doppler broadening positron annihilation spectroscopy (DBPAS)
• Electrochemical impedance spectroscopy (EIS)
• Radiotracer-based transport measurements

Main Results:

• MLD creates an Al-F bond at the EG-alucone/Nafion interface, forming a hybrid region.
• This hybrid region exhibits size-based exclusion properties, enhancing monovalent ion selectivity.
• Post-deposition hydration forms a positively charged alumina layer, further contributing to selectivity.
• Improved Cs+/Na+ and Cs+/Ba2+ selectivity achieved without significant conductivity loss.

Conclusions:

• EG-alucone MLD effectively engineers the Nafion interface for improved ion selectivity.
• A three-layer model explains the structure-property relationship governing selective ion transport.
• This approach offers a promising strategy for advanced membrane separation applications.