(518e) Tuning Transport and Segmental Dynamics in Ionomer Nanocomposites Via Membrane-Nanoparticle Interactions

Ion selectivity of ionomer nanocomposites remains insufficient for the wide-scale implementation of needed energy-storage technologies such as vanadium redox flow batteries. Underlying this issue is an inadequate understanding of how nanoparticles (NPs) incorporated into the ionomer membrane alter the conductive network formed in hydrated state and improve selectivity against vanadium ions. By tuning the surface chemistry of silica NPs, we examine how interactions between the NPs and the ionomer matrix (Nafion) influence the spatial organization of NPs within the ionomer membrane (i.e., the NP ‘dispersion state’), and how the resultant morphology alters vanadium ion permeability and local chain dynamics of the hydrated ionomer. We observe that the NP surface chemistry, and thus the charge of the NP surface, plays an important role in governing the size and degree of NP aggregation, which directly impacts both transport and segmental dynamics. A set of combinatorial spectroscopic techniques was used to resolve the implicit interactions between functionalized SiNPs and Nafion by probing local relaxation dynamics that span across multiple time- and length-scales. Furthermore, anomalous water transport was observed in these membranes, characterized by a combined diffusion-relaxation process. Results obtained from these spectroscopic techniques show congruent trends in changes in local chain dynamics and bulk viscoelastic properties of these membranes under hydration, Findings from this work indicate that both the dispersion state and surface chemistry of the incorporated NPs play a critical role in governing the vanadium ion transport as they each act to slow down the segmental dynamics in these ionomer nanocomposite membranes.