Coaxial electrospun sulfonated poly (ether ether ketone) proton exchange membrane for conductivity-strength balance

Abstract

Coaxial electrospun strategy is proposed to resolve the typical conductivity-strength dilemma of proton exchange membrane and then improve performance of fuel cell. The advantages of co-electrospinning and effects of coaxial components are demonstrated through a simple design of co-electrospun nanofibers, i.e. sulfonated poly(ether ether ketone) with different degree of sulfonation for the core and shell components. The inner nozzle-wall provides extra electrostatic force and enhances microphase separation, as evidenced by the larger ionic clusters and ordered hydrophilic-hydrophobic domains through TEM and SAXS. As a result, the co-electrospun membranes even with the same degree of sulfonation as both the core and shell components exhibit 15.5% increase in proton conductivity and 8.3% decrease in swelling ratio at 80 oC as compared with the uni-electrospun membranes. The low degree of sulfonation core@high degree of sulfonation shell design endows the co-electrospun membranes with relatively high abilities of reinforce (about 51.6 MPa) and proton conduction (about 222.7 mS cm−1 at 80 °C), which indicates the core layer control of strength and shell layer control of proton conduction in the co-electrospun membranes. The H2/O2 cell assembled with the coaxial electrospun membrane exhibits a power density of about 1.3 times that assembled with the commercial benchmark Nafion115.