Synthesis and characterization of multi-block poly(arylene ether sulfone) membranes with highly sulfonated blocks for use in polymer electrolyte membrane fuel cells

• Multi-block sulfonated poly(arylene ether sulfone)s were synthesized.
• SPAES 5 X15Y5 showed similar fuel cell performance to that of NRE212 at 80 °C and 30% RH.
• Distinct phase separation were observed in block copolymer membranes.
• High local concentration of sulfonic acid of naphthalene moiety resulted in higher proton conductivity.

We synthesized novel sulfonated poly(arylene ether sulfone)s (SPAESs) multi-block copolymer membranes containing highly sulfonated hydrophilic blocks. Two different kinds of multi-block SPAESs sharing the same structure of hydrophobic blocks were proposed to investigate the membrane properties based on the effects of the hydrophilic blocks bearing sulfonic acids. The higher local concentration and acidity of the sulfonic acid groups in the hydrophilic block induced higher proton conductivity. The block SPAESs showed comparable proton conductivities to those of the state-of-the-art perfluorinated sulfonic acid (PFSA) membranes, and their transmission electron microscopy (TEM) images revealed a well-developed phase separation. In particular, the SPAES 4 X10Y10 membrane showed excellent proton conductivity, which was higher than that of the PFSA over the entire relative humidity (RH) range at 80 °C. Moreover, the multi-block SPAES membranes showed a comparable fuel cell performance to the Nafion membranes, even at 50% and 30% RH.

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