Development of cation-exchange membranes using solvent-free 3D printing

Abstract

Electromembrane processes are employed in critical applications such as desalination, lithium recovery, and salinity gradient energy conversion. However, issues like fouling and concentration polarisation may limit their effectiveness. Profiled ion-exchange membranes offer several advantages over flat membranes, including improved fluid mixing, enhanced mass transfer, lower pressure drop (thus, lower energy consumption), and elimination of the spacer's shadow effect. Nonetheless, their preparation is considerably more complex than that of flat membranes. In this study, we pioneered the use of solvent-free fused deposition modelling (FDM) 3D printing to fabricate flat and profiled (chevron and stripe) cation-exchange membranes (CEMs). The functionalisation of the 3D-printed membranes into CEMs was achieved via sulfonation. The optimised electrical resistance and permselectivity of the prepared membranes were 10.7 ± 4 Ωcm2 and 97.3 ± 4 %, respectively, after 14 h of sulfonation, closely matching commercial alternatives (e.g., FUMASEP FKB-PK-130, 9.7 ± 3 Ωcm2 and 96.7 ± 1 %). Sulfonation durations exceeding 14 h increased the membranes’ electrical resistance due to the formation of sulfone cross-bridges that do not participate in cations’ exchange. Since FDM 3D printing is a solvent-free and additive manufacturing method, it significantly reduces waste during membrane fabrication, resulting in an E-factor value of 1.5. Therefore, this work opens a path toward customisable, scalable, and greener CEM production for electrochemical applications ranging from the recovery of critical raw materials and water desalination to renewable energy conversion.