Structure and Morphology of Sulfonated Polysulfone and Perfluorosulfonic Acid Ionomers

The limitations of conventional perfluorosulfonic acid (PFSA) based membrane materials have provoked the search for alternative materials which can function as the electrolyte in PEM fuel cells operated at higher temperatures (> 100 °C) and without humidification. A novel class of sulfonated poly(phenylene) sulfone (sPSO2) ionomers have shown much higher proton conductivity than typical PFSA membranes at elevated temperatures. In this dissertation, both computational and experimental methods were used to investigate proton transfer, morphological and structural properties of sPSO2 and PFSA ionomers. We have undertaken ab initio electronic structure calculations to understand the primary hydration and the transfer of protons in oligomeric fragments of sPSO2 ionomers. The effects of equivalent weight, molecular weight and water content on swelling properties of hydrated sPSO2 ionomers were investigated by dissipative particle dynamics (DPD) simulations. The micro-phase separation in hydrated PFSA ionomers was studied by using BF and HAADF imaging in a TEM/STEM. The microstructural evolution as a function of water content is observed and in a good agreement with the results from previous DPD simulations. To understand local chemistry and molecular structures of ionomers, quantitative analyses were conducted based on the results from EELS in the low loss and core loss regions. Finally, the influence of phase transitions and polarization in PTFE chains was determined by comparing experimental and simulated EELS.