TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Arrangement: A fuel cell is provided with electrolyte film, and located between a cathode and an anode.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Clay: The non-modified clay is smectite type clay chosen from montmorillonite, bentonite, saponite, beidellite, nontronite, hectorite and/or stevensite. A clay modifier is added during polymerization.    TECHNOLOGY FOCUS - POLYMERS - Preferred Compounds: The electrolyte film further contains acrylic type polymer which is obtained by curing polyester and hardener of polyhydric alcohol. The polymer (A) is sulfonated polysulfone of formula (1) or (2). The basic polymer (A1) is polybenzimidazole, poly(4-vinylpyridine), polyethylene imine, (acrylamide chlorinated diaryl-di-methyl-ammonium) copolymer, poly(chlorinated diaryl-di-methyl-ammonium), polyacrylamide, polyurethane, polyamide, polyimine, polyurea, polybenzoxazole and/or polypyrrolidone. The polymerizable monomer (B1) is dihalide compound of formula (3), 4,4'-difluoro benzophenone, 4,4'-dichloro benzophenone, m-dichloro benzene, m-difluoro benzene and/or their mixture. The polymerizable monomer (B2) is of formula (4). The diol compound is of formula (5).R1=1-10C alkyl, 2-10C alkenyl, phenyl or nitro group;X=-C(CF3)2-, -C(CH3)2- or -PY'(=O)-;Y'=H or phenyl group;M=H, sodium or potassium;A=sulfonate compound of formula (1-a);A'=sodium sulfonate compound of formula (2-a);Y"=chloride, fluoride, bromide or iodide;p=0-4;m,n=0.1-10;andk=5-500.Preferred Properties: The content of basic polymer (A1) is 0.1-40 mass parts with respect to 100 mass parts of polymer (A). The polymer (A) has number average molecular weight of 10000-300000, mass mean molecular weight of 20000-500000, and sulfonation degree of 40-80%. The reactant mixture is refluxed at 100-160 degrees C to remove water content, and heated at 140-195 degrees C to polymerize the refluxed mixture. EXAMPLE - Sulfate-4,4'-dichloro diphenyl sulfone (0.1 mol), 4,4'-dichloro diphenyl sulfone (0.35 mol), N-methyl-2-pyrrolidone, toluene and potassium carbonate (0.55 mol) were refluxed at 150 degrees C for 12 hours to remove water, and polymerized at 180 degrees C for 6 hours to obtain polymer. The obtained polymer was cooled at 70 degrees C, and montmorillonite (2 g) was dispersed in N-methyl-2-pyrrolidone (20 g). The mixture was stirred, cooled and precipitated to recover sulfonated polysulfone nano composite having sulfonation degree of 60% and number average molecular weight of 60000. The obtained composite (100 mass parts) was dissolved in dimethyl acetamide (200 mass parts), and stirred with polybenzimidazole (5 mass parts). The resulting mixture was applied to a glass substrate, dried at 90 degrees C for 30 minutes to obtain electrolyte film with thickness of 50 mu m. The obtained film, anode and cathode were joined to obtain fuel cell having excellent ionic conductivity, operation efficiency, durability and mechanical strength.