Development of Proton Conductive Polymer Electrolytes Composed of Sulfonated Poly(Ether Ether Ketone) and Brønsted Acidic Ionic Liquid (1-Methylimidazolium Tetrafluoroborate)

This article relates to the synthesis, characterization and dielectric measurements of solid polymer electrolytes, derived from the ionic interaction of sulfonated poly(ether ether ketone) (sPEEK) and a Brønsted acidic ionic liquid (1-methylimidazolium tetrafluoroborate, [Hmim][BF4]), for electrochemical applications. The efficiency of the interaction was examined by incorporating different amounts of ionic liquid (IL) with the sulfonated polymer matrices having three different degrees of sulfonation (DS). The composite electrolytes were systematically characterized with FT-IR, SEM, TGA and DMA analysis. Anhydrous proton conductivity and dielectric measurements were studied in detail as a function of temperature. The presented analyzes revealed that sPEEK1.0-2 sample (2.50–3.51×10− 1 Sm-1 at 380–450 K) exhibited maximum proton conductivity and thermomechanical stability under anhydrous environment. Furthermore, sPEEK1.0-2 composite membrane exhibited higher glass transition temperature and reasonable storage modulus value (Tg = 157 ℃; E' = 0.22 GPa) compared to IL doped sPEEK membranes presented in the literature. The work herein opens new prospects for the as-synthesized materials to use as a solid polymer electrolyte for electrochemical applications such as high temperature proton exchange membrane fuel cells (HT-PEMFC) in a wide temperature range.