Stable ketal-crosslinked anion exchange membranes combining ether-free backbones, piperidinium cations, and rigid–flexible networks

Abstract

Crosslinked anion exchange membranes (NMPDx-NMPy-cQPVB/PVA) are prepared by grafting N-methylpiperidinone and N-methylpiperidine onto poly(4-vinylbenzyl chloride) (PVB) via a Menshutkin reaction, followed by an acid-catalyzed ketal crosslinking with poly(vinyl alcohol) (PVA). The combination of rigid PVB and flexible PVA provides balanced mechanical strength and flexibility, while the ether-free backbone and quaternized N-methylpiperidinium cations ensure promising alkaline stability. The ketal-based crosslinking preserves cation grafting sites, enabling a high degree of functionalization and comparable ionic conductivity. The optimized NMPD20-NMP40-cQPVB/PVA membrane exhibits an in-plane swelling ratio of 3.8% and ionic conductivity of 126.2 mS cm−1 at 80 °C, wet-tensile strength of 10.7 MPa, and elongation at break of 16.6% at room temperature. After 30 days in 1 M KOH at 80 °C, it retains 84.3% of its mass and 91.2% of its conductivity. In water electrolysis operation, the membrane achieves 1.85 A cm−2 at 2.0 V and 80 °C, with a voltage decay rate of 0.125 mV h−1 over 80 h at 1.0 A cm−2.