Non-fluorous hydrocarbon ionomers as substitutes for perfluorosulfonic acid ionomers in polymer electrolyte membrane fuel cell applications.

Currently, the industry standard for polymer electrolyte membrane fuel cells (PEMFCs) are perfluorosulfonic acid ionomer-based (PFSA) ionomers like Nafion®. However, PFSA-based ionomers are expensive to produce, require controlled substances, and can harm the environment through their degradation by-products. They are also susceptible to material degradation, which affects their long-term viability and economic feasibility. Moreover, they lack an efficient end-of-life management system, making them less sustainable. This thesis proposes fully non-fluorous hydrocarbon ionomers to replace PFSA ionomers in PEMFC applications. Alcohol-soluble, highly stable sulfonated phenylated poly(phenylene) biphenyl (sPPB-H+) hydrocarbon solid polymer electrolytes (SPE) are used as both ionomers within the catalyst layer and membrane. The impact of catalyst ink composition on the polarization characteristics of fuel cells incorporating fully hydrocarbon-based membrane electrode assemblies (MEA) is also analyzed. The dependence of fuel cell performance on the nature of the dispersing medium of the catalyst ink is studied using different low boiling point protic solvents. The thesis further investigates the role of catalyst support on the ionic conduction network within the catalyst layer. A novel methodology for PEMFC conditioning is also introduced, accelerated cathode starvation conditioning procedure, for both hydrocarbon and PFSA-based MEAs. The effect of the standardized conditioning protocol was compared with the cathode starvation conditioning protocols. The conditioning protocol's role in the performance and durability of fully hydrocarbon-based MEAs is reported. Finally, this thesis introduces a new method of enhancing fuel cell performance in both fully hydrocarbon-based and PFSA-based PEMFCs. Hydrocarbon-based proton-conducting ionomers are utilized, and highly-branched sulfo-phenylated poly(phenylene) with terphenyl linker (HB-sPPT-H+) ionomer powder is added to address the characteristic poor kinetics, ionic resistance, and mass transport resistance within the catalyst layer utilizing hydrocarbon-based proton-conducting ionomers.