A series
of membranes based on carboxylated polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene (SEBS) were
synthesized via Friedel–Crafts bromoalkylation,
substitution with malonate esters, and heterogeneous ester hydrolysis.
The physicochemical properties of the obtained membranes, including
electrolyte uptake, swelling ratio, and ionic conductivity, were highly
affected by the degree of functionalization and the concentration
of the aqueous KOH solution. Membranes with degrees of functionalization
higher than 100% suffered from excessive swelling and poor mechanical
stability. However, membranes with degrees of functionalization in
the range of 50–75% combined high electrolyte uptake and ion
conductivity with mechanical robustness. The area specific resistance
during electrolysis testing in 15 wt % aqueous KOH at 80 °C was
0.18 Ω cm2 after 1 week, with no signs of degradation.
The H2 in the O2 level at 50 mA cm–2 was about 0.5%, which was considerably lower than that of Zirfon
despite being four times thinner.