Mechanically robust and highly conductive semi-interpenetrating network anion exchange membranes for fuel cell applications

A series of highly transparent semi-interpenetrating polymer network anion exchange membranes (SIPN AEMs) composed of a flexible and cation cross-linked polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (cQSEBS) component, and a rigid, highly-charged quaternized poly(2,6-dimethyl phenylene oxide) (QPPO) component are prepared. Flexible and rigid polymer backbones endow SIPN AEMs with excellent flexibility and mechanical strength. High charge content and well defined hydrophilic/hydrophobic phase separation patterns ensure SIPN AEMs with improved ionic conductivity. Alkali-resistant SEBS, enhanced dimensional stability and ordered microphase separation morphology contribute to the good chemical stability of SIPN-AEMs. Among these AEMs, SIPN-cQSEBS/QPPO-10 with an IEC of 1.93 mmol g−1 achieves a better trade-off between tensile strength (19.36 MPa at 25 °C in wet state), flexibility (58.43% at 25 °C in wet state) and OH− conductivity (103.1 mS cm−1 at 80 °C). Besides, SIPN-cQSEBS/QPPO-10 shows low swelling degree (15.4% at 80 °C) and high chemical stability (95.9%, 88.7%, 82.7% and 88.5% retention in weight, OH− conductivity, tensile strength and elongation at break, respectively, after immersing in 1 M NaOH at 80 °C for 30 days). Importantly, a fuel cell peak power density of 1.174 W cm−2 is obtained at 80 °C by using SIPN-cQSEBS/QPPO-10 as the separator.