Use of a proton exchange membrane M in proton exchange membrane fuel cells, in particular in a polymer electrolyte membrane fuel cell or a direct methanol fuel cell, wherein the proton exchange membrane M comprises at least one partly-sulfonated polybenzimidazole polymer ps-PBI which comprises, in polymerized form, at least 90 mol-% monomeric units U of formula and/or, based on the total amount of monomeric units in the partly-sulfonated polybenzimidazole polymer ps-PBI, wherein L, L 1 and L 2 are selected independently for each of the monomeric units U and are selected, independently from one another, from the group consisting of hydrogen and -A-SO 3 H, wherein A is selected from the group consisting of divalent C 1 -C 10 alkanediyl; divalent C 1 -C 10 fluoroalkanediyl; and divalent C 7 -C 15 arylalkyl; wherein A preferably is selected from the group consisting of divalent linear C 1 -C 10 alkanediyl; divalent linear C 1 -C 10 fluoroalkane; and divalent C 7 -C 12 arylalkyl; Y is selected from the group consisting of O and S, or Y is a single carbon-carbon bond; Z is selected from the group consisting of divalent C 1 -C 10 alkanediyl; divalent C 2 -C 10 alkenediyl; divalent C 6 -C 15 aryl; divalent C 5 -C 15 heteroaryl; divalent C 5 -C 15 heterocyclyl; divalent C 6 -C 19 aryl sulfone; and divalent C 6 -C 19 aryl ether; wherein Z preferably is selected from the group consisting of divalent C 4 -C 8 alkanediyl; divalent C 2 -C 4 alkenediyl; divalent C 6 -C 12 aryl; divalent C 5 -C 12 heteroaryl; divalent C 5 -C 12 heterocyclyl; divalent C 6 -C 12 aryl sulfone; divalent C 6 -C 12 aryl ether; and wherein the total amount of monomeric units U in the partly-sulfonated polybenzimidazole polymer ps-PBI is from about 100 to about 10,000; wherein from about 40 to about 85 mol-% of L, L 1 and L 2, based on the total amount of L, L 1 and L 2, is a moiety -A-SO 3 H; and characterized in that 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 10 -5 S/cm, as measured by impedance method, wherein the proton exchange membrane fuel cell is operated at a temperature of 100 °C or more, preferably in the range of from 100 to 250 °C, under conditions where the proton exchange membrane M is essentially free of water, and wherein the membrane M has a water content of 10 wt.-% or less, based on the total weight of the membrane M. A is selected from the group consisting of divalent C 1 -C 10 alkanediyl; divalent C 1 -C 10 fluoroalkanediyl; and divalent C 7 -C 15 arylalkyl; wherein A preferably is selected from the group consisting of divalent linear C 1 -C 10 alkanediyl; divalent linear C 1 -C 10 fluoroalkane; and divalent C 7 -C 12 arylalkyl; Y is selected from the group consisting of O and S, or Y is a single carbon-carbon bond; Z is selected from the group consisting of divalent C 1 -C 10 alkanediyl; divalent C 2 -C 10 alkenediyl; divalent C 6 -C 15 aryl; divalent C 5 -C 15 heteroaryl; divalent C 5 -C 15 heterocyclyl; divalent C 6 -C 19 aryl sulfone; and divalent C 6 -C 19 aryl ether; wherein Z preferably is selected from the group consisting of divalent C 4 -C 8 alkanediyl; divalent C 2 -C 4 alkenediyl; divalent C 6 -C 12 aryl; divalent C 5 -C 12 heteroaryl; divalent C 5 -C 12 heterocyclyl; divalent C 6 -C 12 aryl sulfone; divalent C 6 -C 12 aryl ether; and