Robust Yet Conductive Blend Anion Exchange Membranes for Hydrogen Production via PPO Reinforcement of Highly Functionalized Styrene–Butadiene-Based Ionomers

Abstract

Herein, vinylbenzyl chloride (VBC)-grafted styrene-butadiene (SB) copolymers, with high contents of VBC (22–32 mol%), were synthesized and blended with low amounts (n = 3–10 wt%) of unfunctionalized poly(phenylene oxide) (PPO). Being well-known for its great chemical compatibility with polystyrene, PPO was selected as non-conductive, hydrophobic and mechanically robust component to be blended with graft copolymers in order to reduce their water uptake, thus improving their dimensional and mechanical stability after quaternization with trimethylamine. The resulting blend membranes were characterized in terms of thermal, mechanical, and ex situ electrochemical properties. Blend membranes generally presented improved mechanical properties, as well as reduced water uptake with respect to AEMs not containing PPO, while retaining ion conductivity values of 11.3–16.6 mS cm−1, higher than that of a commercial hydrocarbon-based benchmark. Among the investigated blend AEMs, g-VBC-32/PPOn membranes were found to have the highest conductivity values (>15 mS cm−1) and the best trade-off between water uptake, mechanical properties and hydrogen permeability. Overall, these results highlight pristine PPO blending as a cost-effective, simple and scalable route to improve the mechanical and dimensional stability of hydrocarbon-based AEMs.