Highly reinforced pore-filling membranes based on sulfonated poly(arylene ether sulfone)s for high-temperature/low-humidity polymer electrolyte membrane fuel cells

Abstract

A series of pore-filling membranes are prepared by impregnating porous cross-linked benzoxazine-benzimidazole copolymer P(pBUa-co-BI) substrates with sulfonated poly(arylene ether sulfone)s (SPAES)s having different degree of sulfonation for polymer electrolyte membrane fuel cells operating at high-temperatures (>100°C) and low-humidity (<50% RH) conditions. The SPAESs are synthesized by reacting 4,4’-dihydroxybiphenyl with the mixtures of disulfonate-4,4’-difluorodiphenylsulfone and 4,4’-difluorodiphenylsulfone in different ratios. The porous P(pBUa-co-BI) substrates are prepared by extracting dibutyl phthalate (DBP) included in P(pBUa-co-BI) films using methanol. The P(pBUa-co-BI) films are prepared by stepwise heating the casted N,N-dimethylacetamide solution containing the mixtures of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI), 3-phenyl-3,4- dihydro-6-tert-butyl-2H-1,3-benzoxazine (pBUa), and DBP to 220°C. The pore-filling membranes are found to have much improved dimensional stability and mechanical strength compared with the SPAES membranes. Although the proton conductivity values of the pore-filling membranes are slightly smaller than those of the SPAES membrane, their cell performance is superior to that of the SPAES membrane at 120°C and 40% RH conditions because ultrathin pore-filling membranes (15–20µm) having high mechanical strength can be prepared and they can contain a larger content of chemically-bound water.