Sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) electrolyte membranes reinforced by electrospun nanofiber porous substrates for fuel cells

This study reports on a novel non-fluorinated composite polymer electrolyte membrane reinforced by an electrospun nanofiber porous substrate (NFPS) having a symmetrically pore-filled structure. Sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) was mechanically reinforced by electrospun and cross-linked bromomethylated poly(2,6-dimetyl-1,4-phenylene oxide) (cBPPO), and the effect of pore-filled SPPO with different ion exchange capacities was investigated. After physical and chemical treatments of the electrospun BPPO nanofiber mat (NFM), proton conducting membranes were successfully fabricated without additional surface conducting layers. In particular, the affinity between hydrophilic conducting SPPO and hydrophobic reinforcing BPPO was considerably improved as both have the same backbone structure. As a result, SPPO based membranes with a high water swelling of 90% were significantly suppressed to 20% due to the mechanical support of cBPPO NFPS. Moreover, the proton conductivities of the prepared membranes were improved from 0.03 to 0.08 S/cm by the increasing IEC, and greatly enhanced performances were confirmed in a H2/O2 fuel cell. Finally, advantages for water management using the prepared thin membranes were discussed in terms of their corresponding polarization behaviors.

Research highlights▶ Chemically and physically processable nanofiber porous substrate (NFPS) is developed. ▶ The NFPS composite polymer electrolyte membranes are successfully fabricated. ▶ The same backbone structure of conductive and support polymer enhances the affinity. ▶ Water swelling of highly sulfonated polymer is significantly suppressed by the NFPS. ▶ Greatly enhanced fuel cell performance and efficient water diffusion are discussed.