Abstract: A method is disclosed of making an ion-conducting composite membrane, the method including: a) combining an electronically and ionically non-conducting polymer, or a blend of at least two such polymers, in solution or in the molten state with low melting point salt; and then b) combining the product obtained from step (a) with hydrolysable organic precursor of silica; and then c) combining the product of step (b) with compatible organic solvent solution of heteropolyacid; and then casting, from the product of step (c), a membrane as a film, preferably a thin film.