Investigation of the Sulfonation Degree on the Membrane's Properties and Its <scp>MFC</scp> Performance

ABSTRACT Proton transport efficiency is a key determinant of the performance of polymer electrolyte membranes in green energy technologies. However, achieving both high proton conductivity and long‐term structural stability simultaneously remains a critical challenge. In this study, a series of sulfonated polysulfone (sPSU) based polymers bearing pendant sulfonic acid chains was synthesized via a facile post‐sulfonation strategy, and the degree of sulfonation was successfully determined. The incorporation of sulfonated pendant chains was designed to promote continuous proton transport pathways and enhance membrane functionality for sustainable energy applications. Comprehensive physicochemical characterization demonstrated that increasing the DS led to an enhancement in water uptake, proton conductivity, and ion exchange capacity. The highly sulfonated sPSU membrane exhibited higher proton conductivity (8.98 mS/cm) than pristine polysulfone (6.92 mS/cm). This improvement is ascribed to the formation of well‐connected hydrogen‐bonded networks facilitated by the pendant sulfonic acid groups, which enable efficient proton hopping through the polymer matrix. Furthermore, the sulfonated membranes demonstrated improved electrochemical performance relative to PSU, showing increases in current density, power density, and energy recovery efficiency. Overall, these findings demonstrate that sPSU membranes with tunable degrees of sulfonation represent promising, cost‐effective, and eco‐friendly candidates for green energy technologies such as MFCs and related electrochemical systems.