A method of making a chloride anion transport membrane comprising preparing a mixture of a rubber, a solvent for said rubber and a powdered ion transport material, providing a layer of the mixture and removing the solvent to produce a dried sheet, said sheet comprising about 50 to 80 volume percent rubber and about 50 to 20 volume percent of said ion transport material, said ion transport material having particle sizes ranging from about 0.01 to 10 microns, said sheet having micropores less than 100 angstroms in diameter, said ion transport material being a salt of a chloride anion and a phosphonium, tertiary ammonium or quaternary ammonium cation.