Successful development of hydrogen separation membranes based on mixed ionic and electronic conductors will improve the economy of hydrogen production. For a gas separation process, interfacial polarization plays an increasingly important role as the ceramic membrane is made thinner to reduce the bulk resistance. In this paper, we report the effect of surface modification on surface properties of a composite membrane consisting of nickel and yttrium-doped barium cerate (Ni-BCY). The application of a Pd thin film on the surface of a Ni-BCY composite membrane significantly reduces the interfacial polarization resistance at temperatures from 500 to 900degreesC. The composition, morphology, and microstructure of the modified membrane surface dramatically influence the catalytic properties for hydrogen separation, (C) 2002 The Electrochemical Society.