Carboxylated\nPolystyrene‑<i>b</i>‑poly(ethylene-<i>ran</i>-butylene)‑<i>b</i>‑polystyrene\nMembranes for Alkaline Water Electrolysis

Abstract

A series\nof membranes based on carboxylated polystyrene-<i>b</i>-poly(ethylene-<i>ran</i>-butylene)-<i>b</i>-polystyrene (SEBS) were\nsynthesized via Friedel–Crafts bromoalkylation,\nsubstitution with malonate esters, and heterogeneous ester hydrolysis.\nThe physicochemical properties of the obtained membranes, including\nelectrolyte uptake, swelling ratio, and ionic conductivity, were highly\naffected by the degree of functionalization and the concentration\nof the aqueous KOH solution. Membranes with degrees of functionalization\nhigher than 100% suffered from excessive swelling and poor mechanical\nstability. However, membranes with degrees of functionalization in\nthe range of 50–75% combined high electrolyte uptake and ion\nconductivity with mechanical robustness. The area specific resistance\nduring electrolysis testing in 15 wt % aqueous KOH at 80 °C was\n0.18 Ω cm² after 1 week, with no signs of degradation.\nThe H₂ in the O₂ level at 50 mA cm^–2 was about 0.5%, which was considerably lower than that of Zirfon\ndespite being four times thinner.