(226bk) Transport Properties of Sulfonated Poly(ether ether ketone) Membranes with Counter-Ion Substitution

Transport properties of sulfonated poly(ether ether ketone) (SPEEK) were analyzed as a function of counter-ion substitution (Ba⁺², Ca⁺², Mg⁺², Mn⁺², Ni⁺², Cu⁺², Zn⁺², K⁺¹) for direct methanol fuel cell (DMFC) applications. The polymeric membranes were characterized using several techniques: elemental analysis (EA), thermogravimetric analysis (TGA), water swelling, and Fourier-transform infrared spectroscopy (FT-IR). The techniques were used to identify the changes in the chemical and thermal properties of the membranes. Proton conductivity and methanol permeability were measured to understand the influence of the sulfonation level and counter ion substitution on the transport mechanism of protons and methanol. Significant differences in their thermal, physical and transport properties were observed when SPEEK was exchanged with counter-ions. The most promising membrane studied was SPEEK exchanged with Ca⁺²; this membrane presented a normalized selectivity (proton conductivity over methanol permeability divided by the respective values of Nafion®) of 36.7.  In addition, the physical and transport properties of SPEEK suggest a different transport mechanism than other sulfonated polymers created by the synergism of the ether-sulfonic groups and morphology.