About the event
The Department of Physics and Astronomy invites all to a colloquium featuring Dr. Eric Sorte, Sandia National Lab. Dr. Sorte will present their talk, “Impact of Hydration and Sulfonation on the Morphology and Ionic Conductivity of SDAPP Proton Exchange Membranes.”
Meet for refreshments before the lecture at 3:45 – 4:10 p.m. in the foyer on floor G above the lecture hall.
Proton exchange members (PEMs) are chemically resistant, electrically insulating, ion-conducting membranes that play a vital role in the operation of batteries and fuel cells. The connection between ionic transport and morphological characteristics in PEMs has been well established, and thus the optimization and control of proton transport/conductivity properties requires a thorough understanding of the membrane’s nanoscale morphology. We have been developing sulfonated Diels Alder poly(phenylene) (SDAPP) membranes as a next-generation PEM polymer candidate; preliminary data have shown that this membrane shows significant improvements over existing PEMs. In this work, we use multiple computational and experimental techniques to understand the morphology and proton transport properties in a series of SDAPP membranes over a wide range of temperature, hydration, and sulfonation conditions. We find good agreement between structure factors calculated from atomistic molecular dynamic (MD) simulations and those measured by X-ray scattering (SAXS). 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 calculated from pulsed-field-gradient (PFG) NMR diffusometry measurements of hydration waters. Comparison of the conductivity obtained by these two methods reveals that the proton conduction mechanism in SDAPP evolves from being dominated by vehicular transport at low hydration and sulfonation to including a significant contribution from the Grotthuss mechanism (also known as structural diffusion) a higher hydration and sulfonation levels. The superior conductivity of SDAPP compared to current PEM technology reflects the impact that evolutions in morphology and the hydrogen bond network, with changing hydration and sulfonation, have on the membrane performance. This atomic-level understanding of SDAPP opens the door to more practically functional membranes with high conductivities and with superior gas barrier properties.