Abstract: Fluorite Ce_0.8Sm_0.2O_2-δ (SDC) nanopowder with a crystallite size of 15 nm was synthesized by a co-precipitation method. An SDC porous layer was coated onto a BaCo_0.7Fe_0.2Nb_0.1O_3-δ (BCFN) mixed conductor to improve its oxygen transport behavior. The results show that the SDC-coated BCFN membrane exhibits a remarkably higher oxygen permeation flux (J_O2) than the uncoated BCFN in the partial oxidation of coke oven gas (COG). The maximum (J_O2) value of the SDC-coated BCFN is 18.28 mL·min^-1·cm^-2 under a COG/air flux of 177 mL·min^-1/353 mL·min^-1 at 875℃ when the thickness of the BCFN membrane is 1 mm; this (J_O2) value is 23% higher than that of the uncoated BCFN membrane. This enhancement is likely because of the higher oxygen ionic conductivity of SDC, which supplies oxygen vacancies and accelerates oxygen exchange on the membrane/coating layer/gas three-phase boundary.