Polarization losses associated with the cathode oxygen reduction reaction and degradation of cathode materials remain as hurdles for widespread implementation of solid oxide fuel cells (SOFC). Rates of degradation depend significantly on the operating temperature and gas conditions, such as the presence of unwanted oxygen- containing compounds, namely H2O and CO2. In this study we explore degradation mechanisms for a common composite cathode material, La0.6Sr0.4Fe0.8Co0.2O3-δ (LSCF) - Ce0.90Gd0.10O1.95 (GDC). Three-electrode cells have been tested under various temperatures, PO2s and contaminant conditions in order to observe changes through electrochemical impedance spectroscopy (EIS). EIS is a powerful tool, which allows us to identify changes in the reaction steps comprising the overall ORR. Our EIS results indicate a strong correlation between blocking effects, caused by CO2 and H2O, and the operating temperature of the cell. Using EIS to deconvolute the overall cathode polarization helps to identify the mechanisms by which degradation occurs.