Tailoring crosslinking in polyketone membranes: Toward stable anion exchange materials for water electrolysis

Polyketone (PK)-based anion exchange membranes (AEMs) were developed and tailored through Paal–Knorr functionalization with 1-(3-aminopropyl)piperidine followed by quaternization using alkyl iodides of different chain lengths. The influence of crosslinker length and degree of crosslinking on thermal, mechanical, and electrochemical properties was systematically investigated. Thermal analysis confirmed sufficient stability for water electrolysis operation, while DSC and stress–strain tests revealed that crosslinking improves mechanical integrity despite the low molecular weight of the PK precursor. Water uptake and ion exchange capacity measurements highlighted the balance between hydrophobicity and charge density, with longer crosslinkers reducing hydration and lower crosslinking degrees increasing swelling. Oxidative and alkaline stability tests demonstrated that membranes crosslinked with longer alkyl chains (DIO, DID) showed improved resistance compared to those with shorter spacers. Conductivity measurements showed that fully crosslinked membranes with long alkyl spacers achieved chloride conductivities close to those of the commercial benchmark Fumasep FAA-3-PK-130, despite exhibiting lower IEC values. Electrochemical testing under alkaline conditions confirmed behavior consistent with AEM water electrolysis systems, indicating promising functional performance. Overall, these findings underscore the decisive role of crosslinker length and density in governing membrane properties and demonstrate that a rational design of PK-based AEMs can effectively balance conductivity, stability, and mechanical integrity, supporting their potential application in green hydrogen production.