The Impact of Quaternization Degree in Polyepichlorohydrin-Based Anion Exchange Membranes on Salinity Gradient Energy Generation by Reverse Electrodialysis

Abstract

Anion exchange membranes with tailored fixed-charge densities can improve monovalent ion selectivity and performance in reverse electrodialysis for salinity gradient power generation. In this study, poly(epichlorohydrin) was blended with polyacrylonitrile and quaternized with 1,4-diazabicyclo[2.2.2]octane at three different molar ratios to produce AEMs with systematically varied quaternization degrees via a one-step amination/ crosslinking procedure. The resulting membranes were characterized for their physicochemical, electrochemical, and RED performance using ATR-FTIR, XPS, SEM, AFM, water uptake, swelling degree, contact angle, surface zeta potential, ion exchange capacity, fixed charge density, and electrical resistance. Higher quaternization increased the IEC, reduced resistance, and shifted surface charge, leading to improved stack power output in model NaCl solutions. In the presence of Na2SO4, power loss was reduced for more highly quaternized membranes, indicating enhanced exclusion of divalent anions (SO42-) and reduced uphill transport. Fouling tests with humic acid/fulvic acid mixtures showed greater stability for quaternized membranes compared to a commercial benchmark. Moreover, stability tests conducted on fouled membranes revealed that the tailor-made membrane exhibits superior durability and lower fouling-induced power loss than commercial Fujifilm Type II AEMs. Overall, these results demonstrate that tuning the degree of quaternization is an effective strategy to balance conductivity and ion selectivity in AEMs for RED applications.