(170g) Impact of Dispersion Processing on Ionomer Thin Films

Ion-conducting polymers (ionomers) are an important component in the heterogenous electrodes (catalyst layers, CL) of energy conversion devices such as fuel cells, electrolyzers, and flow batteries. Ionomer facilitates mass transport to and from the catalyst sites in the CL, which is fabricated through solution-based processing methods. The effect of processing on ionomer structure-property relationships remains largely unexplored. This study aims to understand the impact of processing temperature on supported ionomer thin films (<100 nm), which model the ionomer CL, by characterizing the ionomer in dispersion and after casting into film. Increasing processing temperature leads to changes in ionomer structure in water-alcohol dispersions, observed by pH and small- and wide-angle x-ray scattering (SAXS/WAXS). The structural changes impact thin film morphology, probed via in situ grazing-incidence x-ray scattering (GIXS), and lead to a reduction in hydration, which is correlated with film function in devices. Furthermore, these conformational changes and impact on hydration are shown to be reversible, after cooling the heated dispersions. These results provide insight into the phenomena governing ionomer structure and the resulting film properties.