The effects of EB-irradiation doses on the properties of crosslinked SPEEK membranes

In this study, sulfonated poly(ether ether ketone) (SPEEK) membranes with a crosslinked structure were prepared by the EB-irradiation crosslinking of a mixture of SPEEK and crosslinkers with various irradiation doses. The crosslinked membranes were utilized as proton exchange membranes (PEM) for fuel cell application. The pure SPEEK and crosslinked SPEEK (CSPEEK) membranes were characterized by using 1H and 13C NMR spectroscopy, gel fraction, and a dynamic mechanical analysis (DMA). It was observed that the sulfonic acid groups were introduced exclusively to the hydroquinone segments after the treatment of PEEK with concentrated sulfonic acid and the degree of sulfonation was measured to be 0.69 from the NMR peak integration. The gel fraction study of EB-treated SPEEK membranes indicates that the EB-irradiation doses have a direct effect on the degree of crosslinking. The DMA and SAXS results showed that the CSPEEK membranes have well-developed ionic aggregation in the cluster region. These results indicate that the ionic aggregations of the SPEEK membranes are not largely affected by irradiation. The water uptake of the CSPEEK membranes was found to be lower than 30% at room temperature, and the proton conductivity to be higher than 10−2 S/cm. Finally, the current densities of the CSPEEK membranes irradiated with 50, 100, and 200 kGy, were measured to be 221, 482, and 522 mW/cm2, respectively, at a violated of 0.4 V and at 80 °C. The overall findings suggest that the CSPEEK membranes prepared by EB irradiation are expected to be useful for PEMFC since they exhibit high dimensional stability as well as good cell performance.

► Crosslinked SPEEK membranes were prepared by EB-irradiation method.
► SPEEK with crosslinker mixture was crosslinked successfully by the EB-irradiation.
► The crosslinked SPEEK (CSPEEK) membrane has well-developed ionic aggregation.
► The CSPEEK membrane has a good dimensional stability at high temperature.