Alternative materials for proton exchange membranes: Synthesis of imidazole containing solid and liquid electrolytes

Licentiatavhandling, 2026

To achieve a sustainable future with significantly reduced greenhouse gas emissions, hydrogen has been proposed as an alternative energy carrier. With promising applications in balancing the electricity grid and in the transport sector, proton exchange membrane fuel cells (PEMFCs) are a key technology for realizing such a hydrogen-based society. While already commercially available, current PEMFCs are limited to operating temperatures of about 80 °C due to restrictions imposed by the commonly used membrane materials. This restriction reduces the overall efficiency of not only the cell but also the fuel cell system. Consequently, there is a strong interest in alternative materials that exhibit high proton conductivity at elevated temperatures while maintaining mechanical and chemical stability under acidic conditions. Imidazole, a highly stable amphoteric molecule, offers both hydrogen-bonding capability and proton-accepting sites, making it a promising candidate for such applications. This thesis investigates the synthesis and fundamental properties of materials incorporating imidazole into their structures. Specifically, imidazole is introduced into a covalent organic framework by linker-exchange, into functionalized bases for the synthesis of Brønsted acidic protic ionic liquids, and into aqueous solutions. The developed method for the synthesis of imidazole-linked covalent organic framework provides an alternative synthesis route that leads to increased crystallinity and porosity. The functionalization of alkylated imidazole with electron-withdrawing groups increased the acidity of the resulting protic ionic liquid but decreased its ionic conductivity. Furthermore, investigating imidazole in aqueous solution provided insight into its supramolecular organization and its influence on the proton dissociation of sulfonic acid groups. A deeper understanding of imidazole and its effective incorporation into materials contributes to the knowledge required for the rational design of next-generation proton-conducting systems.