Synthesis of sulfonated poly(bis(phenoxy)phosphazene) based blend membranes and its effect as electrolyte in fuel cells

In the present study, acid-base blend membranes are synthesized to imply as electrolytes in polymer electrolyte membrane fuel cells (PEMFCs). Poly(bis(phenoxy)phosphazene) (POP) is sulfonated with sulfuric acid to impart the ionic conductivity and then blended with sulfonated poly(ether ether ketone) (sPEEK). The blend membranes are fabricated by varying the sulfonated poly(bis(phenoxy) phosphazene) (sPOP) content from 2 to 4 wt.% in relation to sPEEK. The strong hydrophobic backbone of POP improves the mechanical strength of the membrane which is critical for the long term operation of PEMFCs. SAXS analysis suggests the change and enhanced dimension of ionic clusters in sPOP-sPEEK blend membrane in comparison with pristine sPEEK. Hydrophobic and hydrophilic phase distinction in the blend is determined by AFM analysis. Blend membranes exhibit higher ionic conductivity than pristine sPEEK membrane due to the acid-base interactions between sPEEK and sPOP. When subjected to cell polarization, blend membranes of sPOP-sPEEK attain peak power density of 935 mW cm− 2 in PEMFCs which is on par with the peak power density observed for commercial Nafion-212 membrane. Apart from its higher performance, the sPOP (3 wt.%)-sPEEK blend also shows low fuel crossover and comparable stability to Nafion-212 membrane under cell operation.