One of the most promising materials for oxygen separation amongst ceramic oxygen transport membranes (OTMs) is La0.6Sr0.4Co0.2Fe0.8O3 (-delta) (LSCF) due to its relatively high oxygen permeability combined with high stability. In this work, asymmetric thin-film LSCF membranes supported over a porous LSCF support were manufactured by inverse sequential tape casting. Moreover, surface activation was accomplished by depositing a porous LSCF activation layer in order to promote oxygen evolution reaction, i.e. O2- to O-2 oxidation, in the permeate membrane side. In this case, the porous layer allows the surface area available for oxygen activation to be enlarged. Both the manufacturing of the asymmetric thin-film membranes and the surface activation are described in detail. A thorough study of the oxygen permeation is presented for disk-shaped 30 mu m thick LSCF-supported membranes considering the following operating parameters: temperature (1000-600 degrees C), sweep flow rate (300-750 ml min(-1) argon) and oxygen partial pressure in the feed (0.21-1 atm). High permeation fluxes were achieved, e.g., 11.87 ml min(-1) cm(-2) at 1000 degrees C and 300 ml min(-1) argon sweep when using pure oxygen as feed. A change in the apparent activation energy at about 850 degrees C was related to a reversible structural change in the perovskite symmetry (cubic <-> rhombohedral), as revealed by XRD measurements. Furthermore, the application of an activation layer allowed the permeation process to be improved, especially at low temperatures, i.e. below 800 degrees C. Specifically, an improvement of up to about 300% at 600 degrees C is observed upon application of the activation layer. The activated membrane reached a flux of 13.3 ml min(-1) cm(-2) at 1000 degrees C under an O-2/Ar gradient. Additional permeation tests using CO2-rich sweep gas demonstrated the good stability and performance of these LSCF asymmetric membranes at 900 and 1000 degrees C. (c) 2013 Elsevier B.V. All rights reserved.