Friedel-Crafts self-crosslinking of sulfonated poly(etheretherketone) composite proton exchange membrane doped with phosphotungstic acid and carbon-based nanomaterials for fuel cell applications

In this work, self-crosslinked sulfonated polyether etherketone membrane (C-SPEEK) was synthesized by Friedel-Crafts alkylation at 130 degrees C with chloromethylated sulfonated polyether etherketone (SPEEK-Cl). The water uptake (WU) of the C-SPEEK was 47.75% with a 8.69% swelling rate (SR) at 60 degrees C, compared with the sulfonated polyether etherketone membrane (SPEEK) with WU of 110.60% and SR of 57.99%. The contradiction between dimensional stability and proton conductivity under high sulfonation degree was overcome. The self-crosslinking composite membranes were prepared by doping with carbon nanomaterials (Graphite oxide, GO; reduced graphene oxide, rGO and carbon nanotubes, CNTs) and phosphotungstic acid (HPW). Since HPW and carbon nanomaterials incorporated in membrane facilitate protons conduction via both Grotthuss and Vehicle mechanisms, the hybrid membranes demonstrated the improved conductivities. At 80 degrees C, C-SPEEK/HPW/GO showed proton conductivity as high as 119.04 mS/cm, which was 2.4 folds higher than that of the C-SPEEK. Furthermore, the superior performance of C-SPEEK/HPW/GO was further validated through H-2/O-2 single cell test. The C-SPEEK/HPW/GO produced a higher power output of 876.80 mW/cm(2), whereas only 776.72 mW/cm(2) for C-SPEEK was recorded. Thus, C-SPEEK/HPW/GO and C-SPEEK may be promising membrane materials for potential applications in fuel cells.