The composite comprises a polymer matrix formed from a proton-exchange polymer and ionomer particles. The proton-exchange polymer has side chains which have ionic groups. The ionomer particles have an average particle size of less than 20 nm and comprise an oligomeric ionomer that interacts with the proton-exchange polymer and attracts the ionic groups on the side chains of the proton-exchange polymer.
FIG. 12A shows a field emission scanning electron microscopic (FESEM) image of a cross-section of a SPFP Membrane Doped with PSPA-Silica where aggregation of the silica particles can be clearly seen (shown as white dots). The sizes of the silica particles were up to about 0.1 micron. FIG. 12B shows an FESEM image of a cross-section of the SPFP Membrane Doped with PSPA-Silica, where no significant agglomerates were observable. Further, it was observed that the oligomeric ionomer grafted silica particles were uniformly distributed in the membrane matrix, as can be seen in FIG. 12B.