Tuning Interlayer Molecular Weight in Electrodeposited Anion Exchange Membranes for Enhanced Reverse Electrodialysis Performance.

Renewable energy can be harvested from salinity gradients using reverse electrodialysis (RED); however, the open-circuit voltage and power output of this process can be significantly reduced by multivalent ions and natural organic matter found in natural waters. In this work, a tailor-made polyepichlorohydrin-based anion exchange membrane (AEM) surface was modified using an electrophoretic layer-by-layer (LbL) polyelectrolyte assembly. Negatively charged poly(styrene sulfonate) (PSS) and positively charged poly(ethyleneimine) (PEI) were employed to construct three-layer architectures in which PEI served as the interlayer. The results indicate that the molecular weight of the PEI interlayer strongly influences the surface composition and charge of the final AEMs. RED experiments performed in the presence of Na2SO4 revealed that AEMs incorporating the high-molecular-weight PEI exhibited enhanced apparent Cl-/SO42- selectivity and delivered an increased power density. Fouling tests using a real humic-fulvic acid mixture demonstrated that the hydrophilic PSS top layer effectively mitigated organic fouling and preserved RED performance. Furthermore, short-term stability testing provided a preliminary indication of the stability of the polyelectrolyte layers under short-term operating conditions. This study highlights the critical role of interlayer molecular weight in defining the surface chemistry, apparent ion selectivity, and antifouling behavior of LbL-modified tailor-made AEMs, providing important design guidelines for improving RED performance in realistic feedwaters.