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( p BUa- 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 ( p BUa- co -BI) substrates are prepared by extracting dibutyl phthalate (DBP) included in P( p BUa- co -BI) films using methanol. The P( p BUa- 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-2 H -1,3-benzoxazine ( p BUa), 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 (15–20 µm) having high mechanical strength can be prepared and they can contain a larger content of chemically-bound water.