A novel oxygen separation membrane using oxygen ions and a mixed oxygen ion-electron conducting CGO-GBCO (Ce0.8Gd0.2O2 (-) (delta)-GdBaCo2O5 + delta,) dual phase composite has been proposed. The transport and surface exchange properties of the CGO-GBCO composite membrane are investigated as a function of oxygen partial pressure (OPP) over the OPP range of 10(-4) <= pO(2)/atm <= 0.21 at 1073 <= T/K <= 1323 using DC conductivity relaxation experiments. The surface exchange coefficient and the oxygen chemical diffusion coefficient of the composite are similar to those of the CGO-based composite membrane under oxidizing conditions. The characteristic thickness of the specimen, calculated from the oxygen chemical diffusion coefficient and surface exchange coefficient, L-c = (D) over tilde /X is 0.25 mm at 1223 K. The thermally activated oxygen permeation flux monotonically increased with increasing oxygen chemical potential gradient, yielding a maximum of 0.28 cc/min . cm(2) at air/He condition for the 0.62 mm-thick CGO-GBCO specimen at 1223 K. This value is an order of magnitude higher than that of GBCO at the same condition. (C) 2010 Elsevier B.V. All rights reserved.