The electrode reaction of porous La0.6Sr0.4Co0.8Fe0.2O3-delta films deposited onto Ce0.9Gd0.1O1.95 (CGO) Was investigated by impedance spectroscopy within the temperature and oxygen partial pressure (pO(2)) ranges of 500 <= T <= 700 degrees C and 10(-4) < pO(2) <1 atm, respectively, using At and He as gas carriers. The electrochemical impedance spectroscopy (EIS) measurements reveal a high frequency (HF) and a low frequency (U) regions in the Nyquist plane. The high frequency (HF) region was fitted with a Warburg-type impedance element, and the low frequency (LF) region was reproduced with a resistance in parallel to a constant phase element. Both, the slight dependence of the polarization resistance (R-W) and the small variation of the apex frequency (f(v)) of the HF Warburg-type element, on pO(2). Suggest that this contribution corresponds to the oxygen diffusion in the bulk of the La0.6Sr0.4Co0.8Fe0.2O3-delta electrode material. The variation of the polarization resistance of the LF region (R-rcpe) with pO(2) indicates that as T increases, the limiting step evolves from dissociative oxygen adsorption to oxygen gas diffusion in the pores of the mixed ionic/electronic conductor (MIEC) electrode. (C) 2009 Elsevier B.V. All rights reserved.