We have developed double layer-type (catalyst layer/current collecting layer) oxygen electrodes (DLE) for reversible SOFCs. As the catalyst layer (cathode for SOFC and anode for steam electrolysis) interfaced with a samaria-doped ceria [(CeO2)(0.8)(SmO1.5)(0.2), SDC] interlayer/YSZ solid electrolyte, mixed conducting La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and SDC particles were employed. The current collecting porous LSCF layer was formed on the catalyst layer. By controlling the SDC content, as well as the thickness and porosity of the catalyst layer, the gas diffusion rate and the conduction networks for electrons and oxide ions were optimized, resulting in a marked reduction of the overpotential. The LSCF + SDC/LSCF DLE exhibited higher performance than single-layer electrodes of LSCF + SDC or LSCF; the IR-free anode potential vs. an air reference electrode was 0.12V (corresponding to an overpotential of 0.08 V) at 0.5 Acm(-2) and 900 degrees C under an atmosphere of O-2 (1 atm). (C) 2008 Elsevier Ltd. All rights reserved.