Synergistic role of graphene oxide-magnetite nanofillers contribution on ionic conductivity and permeability for polybenzimidazole membrane electrolytes

Abstract Efficient nanofillers within polymeric electrolytes are an interesting design for constructing high-performance membranes for direct methanol alkaline fuel cells. In this work magnetite (Fe3O4) particles are synthesized onto graphene oxide (GO) nanofillers and incorporating into a polybenzimidazole (PBI) matrix for membrane formation. The Fe3O4 nanoparticles are simultaneously anchored onto GO carbon basal planes to form GO-Fe3O4 via the solvothermal process. The pristine PBI, PBI/GO, PBI/Fe3O4, and PBI/GO-Fe3O4 composites are formulated and doped with potassium hydroxide solution to form ionic conductors. GO nanofillers suppress the methanol permeation rate in PBI/GO-Fe3O4 composite membranes while the anchored Fe3O4 nanoparticles result in a bumpy surface, reducing chain packing and promoting anionic conductivity via the loose polymeric free volume. Therefore, the conductivity-to-permeability selectivity of PBI/GO-Fe3O4 composite membrane is improved three times than other samples. The maximum peak power density (Pmax) of a fuel cell employing the PBI/GO-Fe3O4 composite membrane achieves 233 mW cm−2 at 80 °C. The superior power output is attributed to the combined effect of the enhanced anionic conduction resulting from anchored GO-Fe3O4 particles' steric hindrance on polymer chains to enlarged ion diffusion pathways, and the reduced methanol cross-over from the GO's high aspect ratio to retard molecular permeation in the composite membrane.