Construction of proton transport channels in cross-linked composite membrane with highly sulfonated SPEEK nanofibers

Abstract

A series of novel nanofiber composite proton exchange membranes were fabricated by embedding highly sulfonated poly (ether ketone) (SPEEK) nanofibers in a cross-linked SPEEK matrix, showing both high proton conductivity and excellent stability. Composite membranes were prepared with salt-form SPEEK nanofiber mats filled with acid-form SPEEK solution. After thermal treatment at 180 °C in the presence of dimethyl sulfoxide, the cross-linking reaction occurred in the acid-form SPEEK matrix but not in nanofibers. The dimensional stability, mechanical strength, and oxidative stability of the composite membrane were significantly improved due to thermal cross-linking treatment. The swelling ratio of all the cross-linked membranes was below 30% in hot water, and the maximum tensile strength reached 68 MPa. The nanofibers formed non-cross-linked regions and retained rich sulfonic acid groups to construct fast, long-range proton transport channels. The proton conductivity of the nanofiber composite cross-linked membrane reached 200 mS/cm exceeding the pristine cross-linked membrane (135 mS/cm). The fuel cell performance showed a peak power density of 485 mW/cm2 at 80 °C under 100% relative humidity.