Sulfonated silica coated polyvinylidene fluoride electrospun nanofiber-based composite membranes for direct methanol fuel cells

A sulfonated silica coated polyvinylidene fluoride (S-SiO2@PVDF) nanofiber substrate with high strength and ultrahigh surface concentration of sulfonic acid groups was prepared by a three-step simple surface functionalization process. The S-SiO2@PVDF substrate was then used as both mechanical reinforcement support and inter-connected three-dimensional proton transport network for chitosan (CS) to prepare thin composite proton exchange membranes for direct methanol fuel cells (DMFCs). As the mechanical support for CS matrix, the S-SiO2@PVDF nanofiber framework could significantly improve the dimensional stability, tensile strength, elongation and mechanical damage resistance. Meanwhile, as a proton conduction network, the conductivity of the composite membrane was remarkably enhanced to 21.2 mS cm−1 (about 2.8 times than that of pure CS). Moreover, due to the excellent methanol barrier ability of CS matrix itself as well as the limitation role of the nanofibers, the methanol crossover of the composite membrane was as low as 4.2 × 10−7 cm2 s−1 that was only 26% of commercial Nafion 115. DMFC test showed the composite membrane exhibited the maximum power density of 86.3 mW cm−2 (80 °C), and the power density loss was only 5.4% even after operating at a constant current of 0.35A cm−2 for 100 h.