Patent ID: 8148030

Claim:
A production method for making a separation membrane for a fuel cell comprising: preparing a cross-linked hydrocarbon-based anion-exchange membrane; modifying the cross-linked hydrocarbon-based anion-exchange membrane by impregnating at least one side of the cross-linked hydrocarbon-based anion-exchange membrane with a polymerizable acidic compound having weight-average molecular weight, where a weight of a counter cation is eliminated from the molecular weight when its acidic moiety of the compound is neutralized by the counter cation, of 700 or more to less than 8000; and after said impregnating, polymerizing the polymerizable acidic compound; wherein said polymerizable acidic compound is at least one selected from a polyacrylic acid polymer, a polymethacrylic acid polymer, a poly(acrylic acid-methacrylic acid) copolymer and salts thereof; wherein a surface region on at least one side of the separation membrane is highly ion-complexed compared to a central region of the separation membrane.