NOVELTY - Ionic liquid (A) comprises a polymer or copolymer derived from allyl- or vinyl-monomer and containing ammonium-cation (I) and an anion.    USE - (A) is useful as an electrolyte, and in the manufacture of fuel cell membrane or of fuel cell membrane-electrode-unit, preferably a membrane separation process from solvents. (A) is used in polymer membrane matrix (preferably polytetrafluoroethylene or polyethylene terephthalate based systems or oxidic, preferably nanoparticle, coated system and its derivative), which is optionally impregnated with other liquid electrolyte, preferably phosphoric acid. (A) is used as an electrolyte substituent or as an electrolyte additive for protonic acid in membrane systems based on base polymer including polybenzimidazole (preferred), poly(pyridine), poly(pyrimidine), polyimidazole, polybenzthiazole, polybenzoxazole, polyoxadiazole, polyquinoxaline, polythiadiazole or poly(tetrazapyrene) and its derivative. (A) is useful for the retroactive impregnation of porous membrane matrix. (A) is used directly in the separating solution in the manufacture of membranes, or in the polymerization solution in the manufacture of base polymer. (A) is useful in the manufacture of membrane electrode assembly for the impregnation or wetting of electrodes. (A) is useful in a solution for applying or sprinkling the electrode. (A) in combination with a volatile solvent is useful for coating the electrode, preferably in the course of a hot-pressing procedure. (A) is useful as an electrode of membrane electrode assembly (all claimed). The fuel cells are used in mobiles.    ADVANTAGE - (A) influences the water supply or the liquid electrolyte retention of the polymer electrolyte membrane, and reduces the direct methanol fuel cell permeability (claimed). (A) increases the thermal stability of fuel cells, even at high operating temperature. (A) exhibits mechanical stability. The fuel cell from (A) exhibits high oxidation stability, high reduction stability, and low water solubility over the entire operating temperature.    DETAILED DESCRIPTION - Ionic liquid (A) comprises a polymer or copolymer derived from allyl- or vinyl-monomer containing an ammonium-cation of formula (-Q1(X)-Q2(Y1)-) (I) and an anion.    Q1, Q2 = -CH(CH3)-CH2- or -CH2-CH(CH3)-CH2-;    X, Y1 = N+HR1R2, SO3+H, imidazolium, 1-6C alkanesulfonic acid-imidazolium or pyridinium; and    R1, R2 = H or 1-6C alkyl.    INDEPENDENT CLAIMS are included for:    (1) the preparation of the ionic liquid comprising polymerizing the allyl- or vinyl monomer, and subsequently reacting with the corresponding acid compound under anion exchange;    (2) the use of (A) as an electrolyte;    (3) the use of (A) in the manufacture of fuel cell membrane or of fuel cell membrane-electrode-unit, preferably a membrane separation process from solvents; and    (4) a thermal procedure for the preparation of a membrane form (A) comprising the impregnation step.