Comparative study of chemically different structured sulfonic acid and sulfonimide acid of Poly(isatine-phenylene) electrolyte for PEMFC

A hydrocarbon polymer of poly (isatine-phenylene) (PiP), which was synthesized in a super acid-catalyzed polyhydroxy alkylation reaction, was introduced as an alternative conducting material in PEMFC. The sulfonimide acid in super gas-phase acidity was used to modify the sulfonic PiP (SPiP) to improve the dimensional stability and enhance proton conductivity. The PiP (SIPiP) showed considerably higher ion exchange capacity (IEC) and proton conductivity than SPiP controls. All the synthesized polymers revealed excellent thermal stability (<170 °C) and higher IEC (maximum 2.56 meq./g) than Nafion 211®. The study revealed comparable proton conductivity (97.46 mS/cm at 80 °C under 90% RH) and reasonable power density (0.58 W/cm2 at 100% RH and 70 °C) of SIPiP. The chemical structures of the synthesized materials were confirmed by 1H nuclear magnetic resonance (1H NMR) and Fourier-transform infrared spectroscopy (FT-IR), and the polymer morphology was discussed via atomic force microscopy (AFM).