A novel series of cobalt tree dense oxygen permeable dual phase membranes with a composition of 60 wt% Ce0.8Sm0.2O2-delta and 40 wt% Ba0.95La0.05Fe1-xZrxO3-delta (SDC-BLFZ, x=0-0.20) are successfully developed and systematically evaluated as potential oxygen transport membranes for oxy-fuel combustion. The effects of substituting zirconium for iron on the structural characteristics, oxygen permeability, and CO2 resistance of these membranes are studied. Experimental results show that appropriate doping of zirconium slightly decreases the oxygen permeability of the SDC-BLFZ membranes under helium but significantly enhances the structural stability and CO2 tolerance. For the sample with x=0.15, a stable oxygen permeation flux of 0.24 ml min(-1) cm(-2) was achieved at 925 degrees C for a 1.0 mm thick membrane with CO2 as the sweep gas for more than 80 h. This flux value is only 19% lower than that under an air/He gradient, which is much better than that obtained with must alkaline-metal-containing composite dual phase membranes. The enhanced CO2 tolerance of the Zr-cloped SDC-BLFZ membranes is attributed to the declining basicity of BLFZ induced by the substitution of Fe by Zr, as revealed by X-ray photoelectron spectroscopy (XPS). The stable oxygen permeability of the SDC-BLFZ membranes under CO2 demonstrates the potential application of SDC-BLFZ in oxy-fuel combustion technology. (C) 2015 Elsevier B.V. All rights reserved.