(193bh) Elucidating How Interactions between Functionalized Nanoparticles and Nafion Alter the Dispersion State and Vanadium Ion Permeability in Ionomer Nanocomposite Membranes

Nanocomposite membranes have emerged as a promising replacement to traditional polymer electrolyte membranes (PEMs) (e.g., Nafion) for redox flow batteries, a grid-scale energy storage technology for intermittent energy generation. However, traditional PEMs suffer from high vanadium ion crossover, which decreases the lifetime and efficiency of the flow battery. In response, Nafion has been modified with nanoparticles to curtail vanadium ion crossover, but little has been done to understand how the introduction of nanoparticles acts to reduce crossover. Furthermore, studies have shown that the nanoparticles exist in both the hydrophobic and hydrophilic domains, indicating that simple steric hindrance, as previously hypothesized, may not be the only mechanism explaining the reduced crossover. In this study, the surface chemistry of silica (SiO₂) nanoparticles was systematically altered such that the nanoparticles electrostatically and covalently interacted with the hydrophilic domain in Nafion. The nanoparticle functionalization was varied to elucidate if different interactions in PEMs can be used to intelligently tailor nanoparticle dispersion in the membrane (so-called “dispersion state”) and how this degree of dispersion ultimately impacts the vanadium crossover. The nanoparticle loading and diameter were also varied in an attempt to better understand how nanoparticle-Nafion interactions act to reduce vanadium ion crossover in these nanocomposite films. The bridging support between silica nanoparticle surface and end group was also investigated, ranging from a relatively flexible, short saturated chain to a significantly less flexible chain containing aromatic groups. Electron imaging was used to determine the impact of these interactions on dispersion, while vanadium ion permeability was measured via ultraviolet-visible (UV-Vis) spectroscopy. The nanocomposite membranes were also analyzed for their coulombic and energy efficiency to determine the effect of functionalized nanoparticles on membrane performance. Results from this study indicate that the surface functionalization of the silica nanoparticles plays an important role in controlling the permeation of vanadium ions across these nanocomposite membranes.