Characterization of sulfonated polystyrene-block-poly(ethyl-ran-propylene)-block-polystyrene copolymer for proton exchange membranes (PEMs)

Sulfonated polystyrene-block-poly(ethyl-ran-propylene)-block-polystyrene (S-polySEPS) was synthesized by sulfonation at the phenyl groups of polySEPS with the various concentrations of chlorosulfonic acid (CSA). The proton conductivity of the S-polySEPS films was ranged from 10−2 to 10−1 S/cm. In particular, the S-polySEPS film prepared with polySEPS/CSA (molar ratio, 1.0/1.0) has the best proton conductivity (1.36×10−1 S/cm) and water uptake (68%) at 90 °C. Most of the S-polySEPS films have higher proton conductivity and water content than Nafion® 117 at the considering temperature range. The IEC value of the films was improved with increasing the concentration of ionic groups. The TEM image shows that micro-phase separated channels were comprised of ionic-segments displayed within polySEPS matrix. The size of dark ionic channels was about 5–12 nm. The 1H NMR and FT-IR analysis was used to verify the sulfonation of polySEPS. The TGA was carried out to investigate the thermal stability of the S-polySEPS films. The current density of the S-polySEPS film (1100 mA/cm2) prepared with polySEPS/CSA (molar ratio, 1.0/1.0) was higher than that of the Nafion® 117 (680 mA/cm2) at 0.7 V.