Polymer blends for fuel cells based on SPEKK: effect of co-continuous morphologies on water sorption and ionic conductivit

Proton-exchange membranes (PEM), suitable for micro and small sized fuel cells, were obtained by blending sulfonated poly(ether ketone ketone) (SPEKK) polymers with different ionic exchange capacity (IEC). This approach was used to limit the amt. of swelling caused by water sorption without significantly decreasing the proton cond. of the membrane. In particular a membrane with a cocontinuous biphasic morphol. was obtained by blending two SPEKKs, with resp., an IEC equal to 1.2 and 2.08 in the wt. ratio 60/40, casted from 5% (w/v) solns. in dimethylacetamide. The effect of a cocontinuous morphol. on water sorption and proton cond. in comparison to neat SPEKK was investigated. In the range of temps. between 40° and 70°, which is typical for small and micro fuel cells conditions, it was found that the ratio of proton cond. to water sorption could be maximized. This has been attributed to the presence of percolative pathways for proton transport provided by the cocontinuous morphol. along with the constraint effect of the less sulfonated component on the overall capacity of swelling of the membrane.