Abstract: Sustainable power production from salinity gradients can be achieved through reverse electrodialysis (RED). However, although the use of commercial membranes has been extensively reported for this technology, their characteristics constrain overall energy efficiency, constituting the main bottleneck of this technology. For this reason, the present study proposes the fabrication of a nanocomposite cation exchange membrane (CEM), based on a sulfonated polyether sulfone (SPES) polymer matrix and sulfonated silica nanoparticles (S-SiO2 NPs). Prepared membranes were pretreated with an activation protocol to enhance their conductivity. Their specific resistance (RSP) was then analyzed by electrochemical impedance spectroscopy (EIS) to evaluate the influence of S-SiO2 NPs loading, while their performance was assessed in a lab'scale RED system. The results indicate that the optimal S-SiO2 NPs loading was 2.5 wt%. The best performance was achieved with the SPES-SS-2.5-AP2 nanocomposite membrane, which yielded a maximum power density (Pd max) of 1.36 W·m?². This value exceeded those obtained for both the activated pristine SPES membrane and the commercial benchmark (FKS-50). Furthermore, the Pd max achieved with pure NaCl solutions was maintained when using pretreated seawater (SW) as the high concentration (HC) solution with the SPES-SS-2.5-AP2 nanocomposite membrane, suggesting that membrane performance was not dramatically affected by the presence of divalent ions. The findings of this work highlight nanocomposite CEM development, based on S-SiO2 NPs additions into a SPES polymer matrix, as a promising approach for enhancing power production in reverse electrodialysis systems.

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