Multi-Substituted Phosphonated and Sulfonated Polymer Materials: Characterization and Blends with Basic Polymers

Abstract

The growing demand for energy, limited resources, and climate warming call for alternative sustainable energy production. A promising candidate is the proton-exchange membrane fuel cell (PEMFC) using a proton conducting polymer as an electrolyte membrane. The most common proton-exchange membranes are based on sulfonated polymers, such as Nafion®. Since their proton conduction is driven by hydronium ions (H3O+) and hence require water, the operating temperature is limited to 100°C. Unlike in sulfonated polymer materials, the proton conduction in materials with phosphonic acid groups occurs via a hopping process and does not require water.1 This study introduces a highly substituted phosphonated and sulfonated polymer based on poly(pentafluorostyrene), which makes the material adaptable in anhydrous and hydrous operating conditions since the phosphonic acid and sulfonic acid units can conduct cooperatively. The phosphonic acid group is introduced via the nucleophilic aromatic substitution Michaelis-Arbuzov reaction. The Para-Fluoro-Thiol reaction was used to introduce sulfonic acid groups into the polymer backbone. In the past, both reaction steps were well investigated.2,3 The highly substituted polymer material was blended with a basic polymer to circumvent water solubility and investigated according to its proton conductivity, thermal stability, and mechanical properties.(1) Kumar, A. J. Mater. Chem. A 2020, 8 (43), 22632–22636. DOI: 10.1039/d0ta07732a.(2) Atanasov, V.; Oleynikov, A.; Xia, J.; Lyonnard, S.; Kerres, J. Journal of Power Sources 2017, 343, 364–372. DOI: 10.1016/j.jpowsour.2017.01.085.(3) Delaittre, G.; Barner, L. Polym. Chem. 2018, 9 (20), 2679–2684. DOI: 10.1039/c8py00287h.