Submicro-pore containing poly(ether sulfones)/polyvinylpyrrolidone membranes for high-temperature fuel cell applications

A submicro-pore containing proton exchange membrane (PEM) consisting of poly(ether sulfones) (PES) and polyvinylpyrrolidone (PVP) was successfully prepared through a scalable polymer blending method with monodispersed SiO₂ solid spheres as a hard template. After doping with phosphoric acid (PA), an outstanding balance between proton conductivity and mechanical strength in these blends is obtained. The tensile strength of all the porous PES/PVP membranes ranges from 5.98 to 3.69 MPa with an increasing content of SiO₂ from 10 wt% to 50 wt%, which satisfies the mechanical requirements of high-temperature proton exchange membrane fuel cells (PEMFCs). A proton conductivity of 0.09 S cm^-1 is obtained for the as prepared composite membrane with a PA doping level of 350 wt% at 180 °C under anhydrous conditions, comparable with the state-of-the-art PBI/PA membranes. The mechanism for the "balanced" properties is that after the PA doping treatment, the mechanical strength satisfies the requirements of high-temperature PEMFCs with a decreased content of PVP at 50 wt%, while the proton conductivity is improved under the cooperative proton transfers both along the "bonded acid" caged inside the pores and the PA-rich domain formed by "free acid" in the submicro-pores. Furthermore, the PEM fuel cell with PA doped porous PES/PVP exhibits a power density of 454 mW cm^-2 at 180 °C H₂/O₂ without external humidification. A fuel cell performance of ∼520 mV at 0.2 A cm^-2 is maintained for 150 h without obviously decreasing. The submicro-pore containing PES/PVP blends allowed for a higher PA doping level, and consequently, enhanced proton conductivity, as well as improved mechanical strength and cell performance, showing potential for use as an alternative high-temperature PEM for fuel cells under anhydrous conditions.