Effect of Hydration on the Mechanical Properties of Anion Exchange Membranes
Abstract
Anion exchange membranes (AEM) are promising solid polymer electrolytes for use in alkali fuel cells and electrochemical conversion devices. The dynamic nature of the fuel cell environment requires that AEMs operate at a range of hydration levels. Water sorption is critical for ion conduction, but excess water uptake causes dimensional swelling and mechanical instability. Ion conduction is slower in AEMs, compared to proton exchange membranes (PEM), making it important to minimize overall transport resistance by reducing membrane thickness; however, maintaining mechanical durability is difficult as thickness is reduced. Achieving an AEM with high conductivity and good mechanical durability is a difficult balance, which was the focus of this thesis. Various polymer chemistries were investigated with respect to ion conduction, morphology, swelling, and mechanical properties as potential AEMs. The success of perfluorosulfonic acid PEMs inspired synthesis of perfluorinated AEMs, but cation functionalization was low, and proved chemically unstable, resulting in poor performance. Random polyiosoprene copolymers with high ion concentration were solution processed into films and subsequently crosslinked to generate solid AEMs. Diblock copolymers were studied due to their ability to phase separate into organized morphologies for efficient ion transport, but polymer chemistry greatly influenced mechanical performance. A polystyrene based diblock resulted in stiff, brittle AEMs with insufficient strength, but a polyethylene based diblock AEM produced large, flexible films.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 19, 2015
- Accession Number
- ADA624368
Entities
People
- Melissa A. Vandiver
Organizations
- Colorado School of Mines