Perfluorosulfonate ionomer membranes with improved through-plane proton conductivity fabricated under magnetic field

► Superparamagnetic Fe3O4 nanoparticles were synthesized in-situ. ► Fe3O4 nanoparticles were clearly uniaxially aligned in PFSI/Fe3O4 membrane. ► The Fe3O4 in the composite membranes was discarded after membrane fabrication. ► PFSI membranes with through-plane proton conductivity enhanced were fabricated. ► The optimized membrane is anisotropic in through-plane proton conducting.