Hydroxide exchange composite membrane based on soluble quaternized polyetherimide for potential applications in fuel cells

•QAPEIs were successfully synthesized through homogeneous quaternization.•QAPEIs show good solubility in polar solvents.•QAPEI/PTFE composite membranes exhibit high hydroxide conductivity.•QAPEI/PTFE composite membranes show good thermal stability.

A series of soluble quaternized polyetherimides (QAPEIs) have been successfully synthesized by homogeneous quaternization in trimethylamine aqueous solution. 1H NMR spectra confirm the successful synthesis of QAPEI. The QAPEIs exhibit good solubility in membrane-preparation solvents, making it possible to prepare the QAPEI composite membrane. Novel composite hydroxide exchange membranes have been prepared by incorporating QAPEIs with polytetrafluoroethylene (PTFE) membranes. The SEM images, gas permeation measurements and FTIR spectra show that the QAPEI is successfully filled in PTFE membrane and the resulted composite membrane is dense and smooth. The ion exchange capacity of composite membranes ranges from 0.35 to 0.58 mmol g−1. The composite membranes have appropriate water uptake (≤154%) and moderate swelling ratio (≤42%) even at 60 °C. The hydroxide conductivity of the composite membrane reaches 11.9 mS cm−1 at 20 °C that increases to 35.2 mS cm−1 at 60 °C. TGA curve shows that the composite membrane possesses high thermal stability (TOD: 210 °C). All these properties indicate that the QAPEI/PTFE composite membranes are good candidates for use as HEMs in HEM fuel cells.