Phosphoric acid doped imidazolium silane crosslinked poly(epichlorihydrin)/PTFE as high temperature proton exchange membranes

Abstract

Low cost poly(epichlorohydrin) (PECH) was modified with imidazolium groups to prepare high temperature proton exchange membranes. Chloromethyl groups in the structure of the PECH benefit its modification with no need for highly toxic and carcinogenic chloromethylation reagents. Both methylimidazole (MeIm) and triethoxysilylpropyldihydroimidazole (SiIm) were used to carry out the S_N2 nucleophilic substitution for grafting the imidazolium groups onto the PECH. Meanwhile crosslinking of the modified PECH was achieved by forming a crosslinked silane network via the hydrolysis reaction of SiIm in an acid medium. Moreover, porous poly(tetrafluoroethylene) (PTFE) was used as the membrane matrix to enhance the mechanical strength of the fabricated membranes. The obtained PECH–SiIm–MeIm/PTFE membranes displayed phosphoric acid doping capacities of 110–170 wt% with low volume swelling ratios of less than 120%. Anhydrous proton conductivities of 0.010–0.063 S cm⁻¹ were reached at elevated temperatures of 100–180 °C by the membranes with adequate mechanical strength. Fuel cell tests demonstrated the technical feasibility of acid doped PECH–SiIm–MeIm/PTFE membranes for high temperature proton exchange membrane fuel cells.