Polymer blends for fuel cells based on SPEKK: effect of co-continuous morphologies on water sorption and ionic conductivity
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 amount of swelling caused by water sorption without significantly decreasing the proton conductivity of the membrane. In particular a membrane with a cocontinuous biphasic morphology was obtained by blending two SPEKKs, with respectively, an IEC equal to 1.2 and 2.08 in the weight ratio 60/40, casted from 5% (w/v) solutions in dimethylacetamide. The effect of a cocontinuous morphology on water sorption and proton conductivity in comparison to neat SPEKK was investigated. In the range of temperatures between 40 and 70 °C, which is typical for small and micro fuel cells conditions, it was found that the ratio of proton conductivity to water sorption could be maximized. This has been attributed to the presence of percolative pathways for proton transport provided by the cocontinuous morphology along with the constraint effect of the less sulfonated component on the overall capacity of swelling of the membrane.