Electrochemical behavior of the oxygen reduction reaction on La0.72Sr0.18MnO3/Y2O3-ZrO2 (LSM/YSZ) composite and Gd-doped CeO2 (GDC)-impregnated LSM electrodes was investigated in the absence and presence of a Fe-Cr alloy at 900 degrees C in air. The results indicate that for the O-2 reduction on the LSM-based composite electrodes there is an electrochemical transition from a dominant electronic conducting LSM electrode to that of the mixed ionic and electronic conducting (MIEC) oxide such as (La, Sr)(Co, Fe)O-3 (LSCF) as the YSZ content in the LSM/YSZ composites increases. Such a transition occurs at a YSZ content well below the percolation limit of the ionic connectivity of the LSM/YSZ composites. This indicates that addition/impregnation of ionic conducting phases such as YSZ and GDC not only enhances the three phase boundary but also significantly promotes the surface exchange processes for the O-2 reduction reaction on the LSM-based composite cathodes. (c) 2006 The Electrochemical Society.