Anomalous, Multistage Liquid Water Diffusion and Ionomer Swelling Kinetics in Nafion and Nafion Nanocomposites

The advent of commercially viable vanadium redox flow batteries has generated interest in improving upon existing membrane materials utilized in this grid-scale energy storage technology. Elucidating structure–transport relationships in perfluorosulfonated ionomer nanocomposites is of particular importance for the development of next-generation membranes, as there is a limited understanding of how nanoparticles alter transport in these membranes. In the present study, we attempt to resolve the impact of silica nanoparticles (SiNPs) on liquid water transport in Nafion–SiNP membranes. Specifically, liquid water sorption and ionomer swelling kinetics in a series of Nafion–SiNP membranes were evaluated using time-resolved attenuated total reflectance–Fourier transform infrared spectroscopy. Anomalous, multistage water uptake and swelling kinetics were observed for both Nafion and Nafion–SiNP membranes at all SiNP loadings. The first stage of the kinetic data was regressed to a diffusion–relaxation model, as w...