Enhanced Proton Conductivity of Sulfonated Polysulfone Membranes under Low Humidity via the Incorporation of Multifunctional Graphene Oxide

Development of proton exchange membranes with sufficiently high proton conductivity, especially at low relative humidity (RH), remains a big challenge in the field of fuel cells. In this study, graphene oxide-based nanoscale ionic materials (NIMs-GO) were prepared by sulfonation with 3-(trihydroxysilyl)-1-propanesulfonic acid and subsequent neutralization with amino-terminated polyoxypropylene (PO)–polyoxyethylene (EO) block copolymer. The resultant NIMs-GO with acid–base pairs and hygroscopic EO units were incorporated into sulfonated polysulfone (SPSF) to fabricate nanocomposite membranes. A matrix-softening phenomenon was found due to the extensive interaction between the SPSF matrix and the amphiphilic NIMs-GO, which primarily contributes to the homogeneous dispersion of the NIMs-GO filler in the nanocomposite membranes. The acid–base pairs and the interconnected hydrogen-bonded networks formed between the EO units and water molecules imparted efficient proton transfer via the Grotthuss mechanism. The water uptake and retention ability of the SPSF/NIMs-GO nanocomposite membranes were enhanced due to the hydrophilic EO units on NIMs-GO. As a result, the nanocomposite membrane exhibited a 52% increase compared with the pristine SPSF membrane in proton conductivity at 75 °C, 100% RH and a 24-fold increase at 75 °C, 40% RH. This enhanced proton conductivity led to an elevated fuel cell performance under both hydrous and low RH conditions.