An effective alkaline solid electrolyte with magnetic field-aligned Fe₃O₄–GO nanofillers in a polybenzimidazole membrane for methanol fuel cells

In this work, alkaline-doped polybenzimidazole/magnetite–graphene oxide (PBI/Fe₃O₄–GO) nanocomposite membranes are successfully synthesized for enhanced ion conduction and suppressed alcohol permeation for use in direct methanol alkaline fuel cells (DMAFCs). The structural, morphological, and magnetic properties of Fe₃O₄–GO nanofillers are thoroughly investigated. During the membrane drying step, the Fe₃O₄–GO nanofillers are aligned in a polymeric PBI matrix using an applied magnetic field (MF). Without an MF, the nanofillers are randomly distributed in the PBI matrix. The composite membrane with the MF demonstrates a 2- to 3-fold increase in hydroxide conductivity (7.6 × 10⁻² S cm⁻¹) and a one-order of magnitude reduction in fuel permeability (9.96×10⁻⁷ cm² s⁻¹) compared to the other samples. The potassium hydroxide (KOH)-doped PBI/Fe₃O₄–GO composite with MF achieves a higher maximum power density (P_max) of 226 mW cm⁻² at 80 °C than the other samples. The composite membrane with an MF demonstrates good long-term durability of 107 h with low voltage decay (6.5 × 10⁻⁴ V h⁻¹) at high alkaline concentrations (6 M KOH). The results indicate that a small amount (0.5 wt%) of Fe₃O₄–GO nanofillers has an extensive effect on membrane properties in DMAFCs.