Sulfonated Poly (Ether Ether Ketone)-Filled Nanofiber-Based Composite Proton Exchange Membranes for Direct Methanol Fuel Cells

Proton exchange membranes (PEMs) with high proton conductivity, good methanol barrier ability, and reliable mechanical stability are crucial for their practical application in direct methanol fuel cells (DMFCs). Preparation of nanofiber-based composite PEMs is a facile and effective way to balance the trade-off between proton conductivity and mechanical stability of sulfonated poly (ether ether ketone) (SPEEK). Herein, surface amino functionalized silica coated polyvinylidene fluoride (N-SiO2@PVDF) electrospun nanofibers were prepared and used as a mechanical support for SPEEK. The obtained SPEEK-filled N-SiO2@PVDF composite membrane showed a high mechanical strength (27.3 MPa) and good toughness with the aid of the reinforcement effect of nanofibers together with the ionic crosslinking between surface grafted -NH2 and the filling polymer SPEEK. Moreover, the composite membrane demonstrated considerable conductivities especially at 80 degrees C (46.1 mS cm-1), which was very close to that of SPEEK (53.5 mS cm-1). Thanks to its low methanol crossover and high proton conductivity, the single DMFC assembled with SPEEK-N-SiO2@PVDF output higher open circuit voltage of 0.78 V and power density of 70.5 mW cm-2, which were far beyond those of SPEEK (0.66 V and 42.5 mW cm-2).