Synthesis and properties of cation exchange membrane with different fixed group and counter ions
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Authors
Ma, Zongwei
Issue Date
2025-08
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Chemistry
Alternative Title
Abstract
With increasing emphasis on low-carbon economies and sustainable energy systems, electrochemical energy technologies—such as fuel cells, water electrolyzers, and redox flow batteries—have garnered significant attention for their roles in clean energy conversion and storage. A key component in these technologies is ion exchange membrane (IEM), including cation and anion exchange membranes, which serves a vital function in regulating ion transport and maintaining system efficiency.Structurally, a typical IEM comprises a polymeric backbone, ionically charged tethered groups, and associated counterions. These components collectively govern the membrane’s physicochemical properties, including ionic conductivity, mechanical stability, and ion selectivity—parameters that are highly dependent on the specific application and operating environment. Despite extensive research efforts, most studies on cation exchange membranes (CEMs) have focused predominantly on sulfonic acid functional groups, owing to their strong acidic nature and high ionic conductivity in hydrated conditions. In contrast, alternative fixed groups such as phosphonic and carboxylic acids have received comparatively limited attentionIn this work, a series of biphenyl-based polymers bearing distinct fixed ionic groups—sulfonic acid, phosphonic acid, and carboxylic acid—were synthesized via post-functionalization strategies. Membranes were fabricated by solvent casting and subsequently characterized for their mechanical properties using dynamic mechanical analysis. Despite sharing an identical polymer backbone, the polymer membranes exhibited significantly different mechanical responses, underscoring the influence of fixed group chemistry on the polymer network. Additionally, ionic diffusion coefficients and permeabilities were determined for various cations (H⁺, Li⁺, Na⁺, and K⁺). The results indicate that ionic transport properties are primarily governed by (1) the hydration radius of the counter-ions and (2) the binding energy between the mobile ions and fixed groups.In addition, a series of biphenyl-phosphonate/sulfonate blend membranes were fabricated to further explore their potential as high temperature PEMs. These blend membranes exhibited promising proton conductivity under both low and high relative humidity conditions. Notably, the membrane containing 10 wt% biphenyl-phosphonate and 90 wt% biphenyl-sulfonate demonstrated the highest conductivity under low humidity, surpassing that of both the commercial Nafion membrane and the pure biphenyl-sulfonate membrane. Furthermore, the blend membrane showed outstanding mechanical properties, suggesting its suitability for high-temperature fuel cell applications.
Description
August2025
School of Science
School of Science
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY