Cathode degradation is a major issue for solid oxide fuel cells servicing under severe high temperature environments. This work studies the effect of stoichiometry on (La0.6Sr0.4)(x)Co0.2Fe0.8O3 (LSCF) cathode evolution at 800 degrees C by investigating the interfacial reaction and degradation through an AISI 441 interconnect/LSCF electrode/yttria-stabilized zirconia (YSZ) electrolyte half-cell structure under an electric load. Detailed high resolution composition analysis shows that Sr, Co, Fe, and Cr distributions vary with stoichiometry after the thermal treatment. Electron diffraction shows that the new phases are CoFe2O4 and amorphous Cr-oxide for LSCF95, SrCrO4 and CoFeO4 for LSCF100, and CoFe2O4 and CoCr2O4 for LSCF105. Based on the elemental distribution and phase analysis, the evolution of the LSCF electrodes and the interaction mechanisms between the LSCF electrodes and the AISI 441 alloy are proposed. (C) 2014 Elsevier B.V. All rights reserved.