TECHNOLOGY FOCUS - POLYMERS - Preferred Substrate: The porous polymer substrate comprises a lyotropic liquid crystalline polymer, e.g. a polybenzoxazole, polybenzothiazole, polybenzimidazole or polyaramid, e.g. poly(p-phenylene terephthalamide), or a solvent soluble thermoset or thermoplastic aromatic polymer, e.g. a polysulfone, polyethersulfone, polyetherethersulfone, polyarylethersulfone, polyphenylsulfone, polyphenylsulfone, polyimide, polyetherimide, polyphenylene oxide, polyphenylene sulfoxide, polyphenylene sulfide, polyphenylene sulfide sulfone, poly-p-phenylene, polyphenyl-quinoxaline, polyarylketone, polyetherketone, polyether-ether ketone or polyetherketoneketone. The pore size of the substrate polymer is 50-150nm.Preferred Material: The ion conducting material is a sulfonated, phosphonated or carboxylated aromatic polymer, e.g. a sulfonated, phosphonated or carboxylated polyimide or fluoropolyimide, polystyrene-sulfonic acid, poly(trifluorostyrene)sulfonic acid, polyvinyl-phosphonic acid, polyacrylic acid or polyvinylsulfonic acid, or a sulfonated thermoset or thermoplastic aromatic polymer as listed above, or a perfluorinated ionomer, e.g. a carboxyl-, phosphonyl- or sulfonyl-substituted poly(perfluorinated vinyl ether) and has an ion conductivity of 0.1-0.5 S/cm. The membrane is prepared by extrusion or casting a mixture in a common solvent. Alternatively the porous polymer substrate can be impregnated with a solution of the ion conducting polymer or with monomers which are polymerized to produce the ion conducting polymer. The membrane is 0.1-0.5 mil thick and has a specific resistance of 0.2-20 ohm sq.cm. EXAMPLE - Microporous polybenzoxazole film soaked with N-methylpyrrolidone (NMP) was added to a 5 wt.% solution of a 100% sulfonated polyether sulfone in NMP. After 12 hours the film was removed and placed in a 20 wt.% solution of the sulfonated polysulfone in NMP. After 12 hours, the film was removed, stretched in tensioning rings and dried at 5% humidity for 2 days then vacuum dried in an oven at up to 200 degreesC. The composite was hot pressed at 200 degreesC for 5 minutes. The membrane produced had resistance 5.1 ohm sq.cm.