TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The polymeric acid halide is a polyethersulfone, polysulfone, polyphenylsulfone, polyetherethersulfone, polyetherketone, polyetheretherketone, polyphenylene ether, polydiphenylphenylene ether and/or polyphenylene sulfide. The salt, metal oxide or metal hydroxide is prepared by hydrolysis and/or a sol-gel reaction of a precursor, preferably an alkoxide/ester of Ti, Zr, Sn, Si, B or Al, a metal acetylacetonate, preferably Ti(acac)4 or Zr(acac)4 or is a mixed metal/element-alkoxide and metal acetyl acetonate, preferably Ti(acac)2(OiPr)2 or is an organic amine compound of Ti, Zr, Sn, Si, B or Al. The SO2X-, POX2-, COX- or BX2- groups are converted to SO3Y-, PO3Y2-, COOY-, or B(OX)2- groups (Y=H, mono- or divalent metal cation, ammonium, imidazolium, pyrazolium or pyridinium by a hydrolysis reaction after formation of the membrane. The membrane is covalently cross-linked and is post treated with phosphoric acid to generate metal- or element phosphate or -hydrogen phosphate or -dihydrogen phosphate to contribute to proton conductivity.Preferred Process: A thin film is drawn from the polymer solution onto a support (glass or metal plate, textile, felt or porous (polymer) membrane) and the solvent evaporated at 80-150 degreesC at normal pressure or under vacuum and the resulting thin film is post-treated by the following steps which may be carried out in a variable order with the option of not carrying out steps (1), (2) and/or (3), where (1) in water at 50-100 degreesC, (2) in 1-100 wt.% mineral acid (hydrohalic acid, sulfuric acid or phosphoric acid) at 50-100 degreesC, (3) in 1-50 wt.% alkali (ammonia solution, amine solution, sodium hydroxide, potassium hydroxide, sodium carbonate solution, calcium hydroxide solution, barium hydroxide solution) or in an anhydrous liquid amine or mixture of amines, (4) in water at 50-100 degreesC. EXAMPLE - A 70 wt.% solution of zinc (IV) propylate in 1-propanol (0.5307 g) was added to a polysulfone-sulfochloride (0.5 g, 1 sulfochloride group per repeating unit) dissolved in THF (3 g). The resulting mixture was degassed and cast onto a glass dish and allowed to stand overnight at room temperature. The resulting membrane was then treated in 1% NaOH for 24 h at 80 degreesC, in 10% sulfuric acid at 80 degreesC for 24 h and in water for 16 h at 85 degreesC. The membrane had an ion exchange capacity of 0.77 meq SO3H/g, swelling value of 30.9 % and resistance (0.5 NHCl) of 28.9 ohmcm.