Oriented Nanochannel Membranes from Anodized Aluminum Oxide (AAO) and Sulfonated Polystyrene Composites for Flow Battery Applications

Grid-scale power storage remains one of the largest challenges to wide-spread adoption of clean energy technologies with intermittent energy sources (e.g., solar, wind and tidal) and flow batteries are a low cost technology with the potential to meet this need. However, ion exchange membrane materials that are crucial to battery performance have limited operating temperatures, cause resistive losses due to proton transport limitations and lack ion selectivity which leads to electrolyte diffusion across the membrane and performance instability. In this talk, we discuss the use of a new composite membrane structure: anodized aluminum oxide (AAO) filled with sulfonated polystyrene (PSS). AAO was utilized to impart thermal and mechanical stability as well as define the nanochannel size and orientation while PSS and sulfonation level were utilized to control proton transport and ion selectivity. Small angle neutron scattering (SANS) was utilized to characterize the structure of PSS (i.e., filled or partially filled) within the AAO membrane and elemental analysis was utilized to determine the PSS sulfonation level. Membrane performance was characterized utilizing impedance spectroscopy and by examining vanadium cross-over under flow battery operating conditions. These performance metrics are compared to state-of-the-art Nafion membranes and routes towards performance enhancements are discussed.