Use of a proton exchange membrane M in proton exchange membrane fuel cells, wherein the membrane M comprises a blend of (I) at least one polybenzimidazole polymer PBI which comprises, in polymerized form, at least 90 mol-% monomeric units U of formula (I) and/or (II), based on the total amount of monomeric units of the polybenzimidazole polymer PBI, wherein Y is a substituted element selected from O and S; or Y is a single carbon-carbon bond; Z is selected from the group consisting of divalent C1-C10 alkanediyl; divalent C2-C10 alkenediyl; divalent C6-C15 aryl; divalent C5-C15 heteroaryl; divalent C5-C15 heterocyclyl; divalent C6-C19 aryl sulfone; and divalent C6-C19 aryl ether; and wherein the total amount of monomeric units U in the polybenzimidazole polymer PBI is from about 100 to about 10,000; and (III) at least one sulfonated polymer SP, which comprises, in polymerized form, at least 50 mol-% monomeric units U, based on the total amount of monomeric units of the sulfonated polymer SP, wherein at least one of the monomeric units U carries at least one moiety SO3H; wherein the membrane M is essentially free of water and exhibits a proton conductivity at a temperature of 100° C. or more, preferably in the range of from 100 to 250° C. of at least 105 S/cm, as measured by impedance method.
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