Magnetic Field-Assisted Carbon-Based Magnetite Reinforced Chitosan Membranes: The Role of Sulfur Modification in Proton Conductivity and Methanol Barrier for Direct Methanol Fuel Cell

The development of sustainable polymer electrolyte membranes with high proton conductivity and low methanol crossover is a major challenge for direct methanol fuel cells (DMFCs). In this study, chitosan-based composite membranes reinforced with graphene, sulfur-modified graphene, graphene-magnetite, and sulfur-modified graphene-magnetite were fabricated with and without magnetic-field-assisted casting. The effects of sulfur modification and magnetic field-induced structural organization on membrane properties were systematically investigated. FTIR revealed characteristic band shifts and changes consistent with the interfacial interactions between chitosan and graphene-derived fillers, whereas SEM analysis revealed that magnetic field assistance was associated with a more compact and homogeneous morphology. Sulfur modification altered the interfacial characteristics of the graphene-derived filler and was associated with increased water uptake and proton conductivity. Among the investigated membranes, Chi/GEMF exhibited the most favorable membrane-level transport balance, with a proton conductivity of 32.14 mS cm -1 , methanol permeability of (6.65 ± 3.47) × 10 -6 cm 2 s -1 , and the highest membrane selectivity. The observed transport behavior suggests that magnetic field-assisted fabrication can modify the membrane microstructure and transport balance. The results demonstrate the potential of combining a hybrid filler architecture and magnetic-field-assisted processing as a strategy for tuning membrane-level transport properties relevant to DMFC-oriented applications. However, device-level validation using membrane electrode assemblies and single-cell testing is required to establish their practical fuel-cell performance.