Reinforced Saloplastic Anion Exchange Membranes: Balancing Ionic Transport and Mechanical Stability

Abstract

Developing anion exchange membranes (AEMs) that combine affordability, high conductivity, chemical stability, and durability is critical to the practical implementation of many electrochemical processes. Saloplastic AEMs based on polyelectrolyte complexes of poly(styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) meet several of these criteria, offering low-cost fabrication, good alkaline stability, and the additional advantage of sustainable processing. A major remaining challenge in the development of saloplastic AEMs is achieving sufficient mechanical stability. In the present study, this limitation was addressed by reinforcing saloplastic AEMs with woven mesh supports. To mitigate conductivity losses from non-conductive reinforcements, membrane thickness was reduced using a spacer-free hot-pressing approach, in which the apparent viscosity of the polyelectrolyte complex was tuned by salt concentration. This strategy allowed the fabrication of thin, mechanically stable, and defect-free membranes, thereby minimising membrane area resistance. Reinforcements spanning a range of thicknesses and open areas were systematically investigated to decouple their effects on mechanical and transport properties. While thinner reinforcements minimised area resistance, a lower reinforcement open area strongly enhanced tensile strength with only a minor impact on ionic conductivity. Guided by these findings, a thin reinforcement with a 22% open area was selected to improve mechanical stability, increasing the tensile strength from 1.1 ± 0.2 MPa for the non-reinforced membrane to 62 ± 2 MPa. Furthermore, a substantial reduction in membrane thickness resulted in ~30% lower area resistance compared to the non-reinforced membrane. Overall, this work demonstrates that saloplastic membrane properties can be tailored to specific applications by tuning reinforcement architecture and membrane thickness to balance mechanical stability and ionic transport.