Performance and stability of ether-free high temperature proton exchange membranes with tunable pendent imidazolium groups?

Journal of Materials Chemistry A Pub Date: 2022-11-01 DOI: 10.1039/D2TA07129K

Abstract

(Benz)imidazoliums are demonstrated to be effective for the retention of phosphoric acid (PA) in PA doped proton exchange membranes (PEMs) due to the formation of (benz)imidazolium–biphosphate ion-pairs. However, there is less research on the stability of the polymer materials with pendent (benz)imidazoliums. Herein, novel ether-free poly(biphenyl isatin-co-imidazolium)s (PIBI-Qx) were prepared as PA doped PEMs via a one-step superacid catalysed polycondensation and methylation process. The dissolution of PA/PIBI-Qx membranes at high temperature can be inhibited effectively via tuning the methylation degree of the pendent imidazole. Moreover, the PA retention and conductivity retention of the PA/PIBI-Q70 (70% imidazolium content) membrane are over 20% and 30% higher than those of the PA/mPBI membrane, respectively, after 100 h at 80 °C/40%RH. Thus, the corresponding cell is stable for at least 60 h at 160 °C with 8% RH, while a significant drop of 27% in the peak power density is observed for the PA/mPBI membrane-based cell. Furthermore, the thermal/acidic stability of PIBI-Qx membranes with pendent imidazolium groups was studied, and two dominating degradation mechanisms e.g. “de-methylation” of imidazolium and “retro-Friedel–Crafts reaction” in the polymer backbone are verified via XPS spectral analysis.

Graphical abstract: Performance and stability of ether-free high temperature proton exchange membranes with tunable pendent imidazolium groups
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