Nanocomposite membrane with superior proton conductivity based on sulfonated poly (ether ether ketone)/carbon quantum dot/sulfonated graphene for direct methanol fuel cell

In the present study, a novel membrane was prepared by integrating carbon quantum dot/sulfonated graphene (CQD/SG) into sulfonated poly (ether ether ketone) (SPEEK). The functionalization of graphene and the anchoring of hydrophilic CQD on it creates new and continuous proton transfer sites in the polymer matrix. Incorporating CQD/SG in SPEEK resulted in increased proton conductivity compared to pure SPEEK. This improvement is due to increasing polymer and nanosheet interface interactions and reduction of the energy barrier through the Grotthuss mechanism. Nanocomposite membrane with 5%wt of CQD/SG as an optimized nanocomposite has the lowest swelling ratio (14.63%) and the highest ion density (3.58 mol/L), effective proton mobility (1.9 × 10⁻⁴ cm² /s V), proton conductivity (0.066 S/cm), and water absorption (44.66%) than other membranes at 30 °C. Also, this nanocomposite membrane has a higher proton conduction (0.195 S/cm) at 80 °C than Nafion 117.