Zr0.84Y0.16O1.92 (YSZ)-La0.8Sr0.2Cr0.5Fe0.5O3-delta (LSCrF) planar membranes consisting of an oxygen-permeable dense layer and a finger-like porous support were prepared using the phase inversion tape casting/sintering method. The thickness of the dense layer was varied in the range of 75-25 mu m by adjusting the blade gap for the tape casting. The oxygen permeation flux through the membranes was measured at elevated temperatures with the dense layer side exposed to air and the porous support side swept with CO to remove the permeated oxygen. At 850 degrees C, oxygen permeation fluxes of 0.8, 0.9, 1.1 ml cm(-2) min(-1) (STP) were observed for the membranes with a 75, 50, 25 mu m thick dense layer, respectively. The oxygen permeation flux increased with decreasing the thickness of the dense layer appreciably, but the increment was much smaller than the extrapolated value assuming the linear dependence of the oxygen permeation flux on the reciprocal thickness, revealing that the overall oxygen permeation process was mainly controlled by the surface oxygen exchange step in the given thickness range. To enhance the surface oxygen exchange activity, the membrane was modified by applying a 10 mu m thick porous YSZ-LSCrF layer on the dense layer side surface and depositing samarium doped ceria (SDC) nano-particles on the inner surface of the porous support. The membranes with modified surfaces exhibited much increased oxygen permeation flux. An increased flux of 2.1 ml cm(-2) min(-1) was obtained at 850 degrees C for the membranes with a 25 mu m thick dense layer, which was almost twice as large as that for the un-modified membrane. The membrane with a thin dense separation layer and modified surfaces shows much increased oxygen permeation flux, promising for practical applications. (C) 2016 Elsevier B.V. All rights reserved.