Dual cross-linked organic-inorganic hybrid polymer electrolyte membranes based on quaternized poly(ether ether ketone) and (3-aminopropyl)triethoxysilane

Quaternized poly(ether ether ketone)s (QPEEKs) are synthesized to absorb phosphoric acid (PA) and used as high temperature proton exchange membranes (HTPEMs). In order to improve their oxidative and mechanical stability without sacrificing proton conductivities, a series of dual cross-linked organic-inorganic hybrid membranes are prepared using (3-aminopropyl)triethoxysilane (APTES) as a cross-linker. The amine of APTES reacts with two benzyl bromide groups to build the primary cross-linking network. The Si–O–Si network generated by the hydrolysis of triethoxysilane in APTES is the secondary cross-linking network. The dual cross-linking hybrid networks improve the mechanical and oxidative stability of PA doped membranes. They can endure up to 15.3 h in 3 wt.% H2O2, 4 ppm Fe2+ Fenton solution at 80 °C. During the hydrolysis of triethoxysilane, the release of small molecules (H2O and C2H5OH) forms many pores in surfaces and interior of membranes. These pores and the resulted Si–OH groups corporately enhance the PA absorbing ability and proton conductivity. The highest proton conductivity is 61.7 mS cm−1 for PA-QPEEK-10%APTES at 200 °C under anhydrous condition. These membranes show great potential to be used in HTPEM fuel cell. •The dual cross-linked organic-inorganic hybrid membranes were prepared.•The pores were formed in surfaces and interior of membranes by cross-linker.•Both the pores and Si–OH groups contributed to improving proton conductivity.•The connective phosphoric acid clusters could improve proton conductivity.