TECHNOLOGY FOCUS - POLYMERS - Preferred Film: The polymeric electrolyte film comprises hydrocarbon group polymer. The polymer electrolyte film has ion exchange capacity of 2-4 mequivalent/g, and electric conductivity of 0.2 S/cm or more and 0.01 S/cm or more at 80degreesC and relative humidity of 95%, and 80degreesC and relative humidity of 50%, respectively. The polymer electrolyte film does not dissolve in 80degreesC water. The polymeric electrolytic film comprises co-polymerized aromatic polymer having sulfonic acid group chosen from polysulfone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone and polyether ketone. Preferred Polymer: The aromatic polymer has sulfonyl group-containing structure of formula (1) in a molecule, aromatic group-containing structure of formula (3): -(Ar1-Z3-Ar'-Z3), sulfonyl group-containing structure of formula (11) and aromatic group-containing structure of formula (12).X=-S(=O)2- group or -C(=O)- group, preferably -S(=O)2;Y'=hydrogen or monovalent cation, preferably hydrogen atom;Z1=oxygen atom or sulfur atom, preferably oxygen atom;Ar,Ar'=bivalent aromatic group, preferably group of formula (2), or group chosen from 7 claimed groups, such as group of formulae (9A,9B), more preferably group of formula (10);Ar1,Ar2=bivalent aromatic group, preferably group chosen from group of formulae (5-8), more preferably group of formula (8);Z2=oxygen atom, sulfur atom, -C(CH3)2-, -C(CF3)2-group, -CH2- group or cyclohexyl group, preferably oxygen atom;n1=3 or more;R=1-4C alkyl;r=0-2;X=-S(=O)2- or -C(=O)-group;andZ5,Z6=oxygen atom or sulfur atom.Preferred Composition: The ratio of moles of structure (1) with respect to total of moles of structure of (1) and structure (3) is 0.3-0.7. The ratio of sum of moles of structures (11,12,1,3) with respect to sum of moles of structures (1,3,11,12), and other repeating unit is 0.9-1. The ratio of sum of moles of structures (11,12) with respect to sum of moles of structures (1,3,11,12) is 0.3-0.7. The ratio of sum of moles of structures (1,3) with respect to sum of moles of structures (1,3,11,12) is 0.01-0.95.