Magnetically aligned composite membranes based on sulfonated poly(ether ether ketone) and phosphotungstic acid-loaded magnetic nanoparticles for fuel cell

In this work, phosphotungstic acid (HPW)-loaded polydopamine-coated magnetic nanoparticles (DMNPs@HPW) were prepared and incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix with magnetic field assistance to construct aligned channels to shorten proton transport pathways. The structure of the prepared composite membranes (M-SP/DMNPs@HPW) with magnetic field-induced proton channels was confirmed by SEM. The proton conductivity of M-SP/DMNPs@HPW-2 was significantly improved, with in-plane proton conductivity (σ//) of 159.3 mS/cm and through-plane proton conductivity (σ⊥) of 129.2 mS/cm in the hydrated state at 80 °C, which were 1.31 and 1.57 times higher than the pristine SPEEK membrane, due to the strong acidity of HPW and acid-base interaction of amine and sulfonic acid groups. Meanwhile, the σ⊥ of M-SP/DMNPs@HPW-2 was 1.14 times higher than that of SP/DMNPs@HPW-2 membrane prepared without magnetic field assistance. The fuel cell power output of M-SP/DMNPs@HPW-2 was 433 mW/cm2, while SP/DMNPs@HPW-2 and pristine SPEEK membranes tested under the same conditions were 360 mW/cm2 and 277 mW/cm2, respectively. The hydrogen crossover of M-SP/DMNPs@HPW-2 was slightly increased compared to SP/DMNPs@HPW-2 due to the construction of through-plane proton transport channels in the membrane.