Quaternary Ammonium-Functionalized Siloxane Semi-IPN for SPEEK Membranes: Decoupling the Conductivity–Stability Trade-Off

Balancing high proton conductivity with dimensional stability remains a persistent “trade-off” for sulfonated poly(ether ether ketone) (SPEEK) electrolytes. Herein, an amine-triggered self-catalyzed strategy is reported to construct a quaternary ammonium-functionalized siloxane semi-interpenetrating polymer network (semi-IPN) within SPEEK matrix. The in-situ formed rigid Si─O─Si scaffold effectively confines membrane swelling, while the tethered quaternary ammonium sites synergistically facilitate efficient proton hopping through acid–base interactions with sulfonic acid groups. The optimized membrane (GTM-2) yields a peak conductivity of 277.8 mS cm −1 at 80°C, achieves a power density of 746.26 mW·cm −2 in a single fuel cell. Moreover, the semi-IPN membranes maintain favorable mechanical strength (up to 23.3 MPa). This architectural design provides a robust pathway for developing high-performance, non-fluorinated proton exchange membranes.