Unravelling the Interplay Between Structural Dynamics and Water Transport in Perfluorosulfonated Ionomer Nanocomposites Through the use of Neutron Scattering and Infrared Spectroscopy

Ionomer nanocomposites are attractive as proton exchange membranes in redox flow batteries, as they combine the thermo-chemical resistance of perfluorosulfonated ionomers with the reduced vanadium ion transport due to the presence of silica nanoparticles (SiNPs). However, elucidating the impact of SiNPs on the structural ordering and transport properties of these nanocomposites is an ongoing challenge. In this study, neutron spin echo (NSE) spectroscopy and high flux backscattering (HFBS) spectroscopy were employed to probe changes in polymer segmental dynamics and water dynamics, respectively, while small-angle neutron scattering (SANS) was used to investigate the SiNP dispersion state. In tandem with these techniques, infrared spectroscopy was used to capture water transport and water-induced swelling of the ionomer nanocomposites. Data from this complementary set of techniques indicate that SiNPs inhibit both viscoelastic relaxations and segmental dynamics of the ionomer network. Further, ionomer swelling and water transport in these nanocomposites were found to be highly coupled, leading to a complex water transport mechanism in these membranes. Finally, SiNP surface chemistry was established as a handle for tunability for ionic transport in perfluorosulfonated ionomers.