Impact of Hydration and Sulfonation on the Morphology and Ionic Conductivity of Sulfonated Poly(phenylene) Proton Exchange Membranes

Journal Article · Tue Jan 15 00:00:00 EST 2019 · Macromolecules

DOI:https://doi.org/10.1021/acs.macromol.8b02013· OSTI ID:1492390

Sorte, Eric G. ^[1]; Paren, Benjamin A. ^[2]; Rodriguez, Christina G. ^[3]; Fujimoto, Cy ^[4]; Poirier, Cassandria ^[1]; Abbott, Lauren J. ^[5]; Lynd, Nathaniel A. ^[3]; Winey, Karen I. ^[2]; Frischknecht, Amalie L. ^[5]; Alam, Todd M. ^[1]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Dept. of Organic Materials Science
2. Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering
3. Univ. of Texas, Austin, TX (United States). McKetta Dept. of Chemical Engineering
4. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Nanoscale Sciences Dept.
5. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Center for Integrated Nanotechnologies

Multiple computational and experimental techniques are used here to understand the nanoscale morphology and water/proton transport properties in a series of sulfonated Diels–Alder poly(phenylene) (SDAPP) membranes over a wide range of temperature, hydration, and sulfonation conditions. New synthetic methods allow us to sulfonate the SDAPP membranes to much higher ion exchange capacity levels than has been previously possible. Nanoscale phase separation between the hydrophobic polymer backbone and the hydrophilic water/sulfonic acid groups was observed for all membranes studied. We find good agreement between structure factors calculated from atomistic molecular dynamics (MD) simulations and those measured by X-ray scattering. With increasing hydration, the scattering ionomer peak in SDAPP is found to decrease in intensity. This intensity decrease is shown to be due to a reduction of scattering contrast between the water and polymer and is not indicative of any loss of nanoscale phase separation. Both MD simulations and density functional theory (DFT) calculations show that as hydration levels are increased, the nanostructure morphology in SDAPP evolves from isolated ionic domains to fully percolated water networks containing progressively weaker hydrogen bond strengths. The conductivity of the membranes is measured by electrical impedance spectroscopy and the equivalent proton conductivity calculated from pulsed-field-gradient (PFG) NMR diffusometry measurements of the hydration waters. Comparison of the measured and calculated conductivity reveals that in SDAPP the proton conduction mechanism evolves from being dominated by vehicular transport at low hydration and sulfonation levels to including a significant contribution from the Grötthuss mechanism (also known as structural diffusion) at higher hydration and sulfonation levels. The observed increase in conductivity reflects the impact that changing hydration and sulfonation have on the morphology and hydrogen bond network and ultimately on the membrane performance.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Univ. of Pennsylvania, Philadelphia, PA (United States)
• Sponsoring Organization: National Science Foundation (NSF) (United States); SNL Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC)
• Grant/Contract Number: NA0003525
• OSTI ID: 1492390
• Report Number(s): SAND--2018-9649J; 667559
• Journal Information: Macromolecules, Journal Name: Macromolecules Journal Issue: 3 Vol. 52; ISSN 0024-9297
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY