Poly(sulfonated phenylene)-block-poly(arylene ether sulfone) copolymer for polymer electrolyte fuel cell application

Abstract Novel poly(2-(3-sulfo)benzoyl-1,4-phenylene)- block -poly(arylene ether sulfone) copolymers (PSP- b -PAESs) were successfully synthesized by Ni(0)-catalyzed copolymerization of 2,5-dichloro-3′-sulfo-benzophenone (DCSB) and chlorobenzophenone-endcapped oligo(arylene ether sulfone). Their physical property, morphology and polymer electrolyte fuel cell (PEFC) performance were investigated compared to those of the DCSB-based random copolymers and Nafion112. PSP- b -PAES with a measured ion exchange capacity (IEC) of 1.82 meq g −1 , of which the hydrophilic/hydrophobic block lengths were evaluated as 17/8.4, showed the relatively small number of water molecules sorbed per sulfonic acid group ( λ  = 15) in water and the anisotropic membrane swelling with 2.4 times larger through-plane swelling than in-plane one, whereas it showed the almost isotropic proton conductivity. The PSP- b -PAES exhibited a microphase-separated structure composed of hydrophobic and hydrophilic domains, whereas the random copolymers exhibited a homogenous morphology. The PSP- b -PAES had the larger proton conductivity than the random copolymer with an IEC of 2.01 meq g −1 , especially under the low relative humidities. Even at a low humidification of 17% RH at 90 °C and 0.2 MPa, the PSP- b -PAES exhibited the high PEFC performance; namely, cell voltage of 0.69 V at load current density of 0.5 A cm −2 and maximum output of 0.73 W cm −2 , which were much higher than those at 30% RH for the random copolymer (0.65 V and 0.51 W cm −2 ) and Nafion112 (0.70 V and 0.61 W cm −2 ). The PSP- b -PAES showed the fairly high durability of 750 h under PEFC operation at 90 °C in spite of the relatively low molecular weight. PSP- b -PAESs have the high potential as polymer electrolyte membrane for PEFC applications.