Development of proton conductive polymer electrolytes composed of sulfonated poly(ether ether ketone) and Brønsted acidic ionic liquid (1-methylimidazolium tetrafluoroborate)

Mesut Yılmazoğlu

doi:10.1007/s10854-021-06089-w

Abstract

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 polymer matrices and composite electrolytes were systematically characterized with 1H NMR, FT-IR, SEM, TGA and DMA. Anhydrous proton conductivity and dielectric measurements were studied in detail with varying temperature and frequencies. 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. Dielectric measurements also provided results confirming proton conductivity measurements. Furthermore, sPEEK1.0–2 composite membrane exhibited higher glass transition temperature and reasonable storage modulus value (Tg = 157 °C; 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.

Highlights

Proton exchange membrane fuel cells (PEMFC) have been received as the most attractive fuel cell type due to rapid start-up, high energy efficiency and environmentally friendly operation conditions
The basic idea in the use of sulfonated poly(ether ether ketone) (sPEEK) and ionic liquid (IL) is that the ionic interaction between the sulfone groups in the polymer matrix and the cation group imidazole in the IL structure improves proton conductivity
In case of Tg values, it was observed that the Tg of the sPEEK-2 membrane was similar to the other studies presented in the literature, whereas in this study, the high proton conductive composite membrane obtained by IL doping process showed a higher Tg value than the IL doped membrane electrolytes presented in the literature (~ 70–90 °C) [51]

Summary

Introduction

Proton exchange membrane fuel cells (PEMFC) have been received as the most attractive fuel cell type due to rapid start-up, high energy efficiency and environmentally friendly operation conditions (no waste other than pure water). Approaches to the usage of ILs in the development of membrane electrolytes in fuel cells are diversified in the literature as processes i) where ILs are used directly as electrolytes [30], ii) using membrane electrolytes obtained by the addition of ILs to the polymer backbone [31], iii) using functional polymer electrolytes obtained by polymerization of IL-soluble monomers [32] and iv) using electrolytes obtained by the polymerization of polymerizable ILs [33] Polymer materials such as poly(arylene ether ketone) (PAEK), polysulfone (PS), polyimide (PI), polybenzimidazole (PBI) and poly(ether ether ketone) (PEEK) have been presented as promising membrane materials for electrochemical applications due to their superior chemical/thermal strength and easy processability. The proton conductivity and dielectric measurements of the composite membranes were determined and the effect of DS and IL addition on the proton conductivity and thermal/mechanical properties were discussed

Materials

Characterizations

Results And Discussion

Proton conductivity tests

Conclusion

Ethical Approval