Exposure of solid oxide fuel cell (SOFC) cathode materials to contaminants has an immediate affect on the kinetics of the oxygen reduction reaction (ORR), as well as the performance of the cell as a function of time. Typical contaminants that are found during operation of SOFCs are CO₂ and H₂O from ambient air, and chromium from stack or interconnect materials. It is important to note that during regular operation, cathode mateirals may be exposed to all of these contaminants simultaneously. Our results show a significant effect of CO₂, H₂O, and Cr, on the performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF)-Ce_0.90Gd_0.10O_1.95 (GDC) composite cathodes. Interestingly, this effect varies depending on the concentrations of oxygen and the contaminants, as well as temperature and other operating conditions, such as applied bias. We have found that at decreased temperatures, both CO₂ and H₂O decrease the performance of LSCF-GDC cathodes. This will become more significant as the field as a whole drives toward reduced-temperature SOFCs. We have focused on the effects of these contaminants on LSCF-GDC composite cathodes, as LSCF is still one of the most promising materials for intermediate and low-temperature SOFCs, but have also extensively investigated the effect of contaminants on LSM and LSM-YSZ composite cathodes. Experiments have been performed to investigate both the short-term (kinetic) and long-term (stability) influence of contaminants on cathode materials using electrochemical impedance spectroscopy (EIS) as the main tool. Post-mortem X-ray diffraction and electron microscopy was used to investigate irreversible changes that occurred in the samples. The results suggest that in the presence of different contaminants surface reaction kinetics on LSCF vary, and that the changes in kinetics correlate to the concentration of contaminants. In addition, applied bias shows a high impact on the interactions of contaminants with cathodes. Further, cross-contamination, such as air with H₂O+CO₂, increases overall polarization resistance of the cathode beyond exposure to a each individually. This study aims to elucidate mechanistic routes for contaminant degradation, and in doing so, provide information useful for the further development of reduced temperature SOFCs.Exposure of solid oxide fuel cell (SOFC) cathode materials to contaminants has an immediate affect on the kinetics of the oxygen reduction reaction (ORR), as well as the performance of the cell as a function of time. Typical contaminants that are found during operation of SOFCs are CO₂ and H₂O from ambient air, and chromium from stack or interconnect materials. It is important to note that during regular operation, cathode mateirals may be exposed to all of these contaminants simultaneously. Our results show a significant effect of CO₂, H₂O, and Cr, on the performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF)-Ce_0.90Gd_0.10O_1.95 (GDC) composite cathodes. Interestingly, this effect varies depending on the concentrations of oxygen and the contaminants, as well as temperature and other operating conditions, such as applied bias. We have found that at decreased temperatures, both CO₂ and H₂O decrease the performance of LSCF-GDC cathodes. This will become more significant as the field as a whole drives toward reduced-temperature SOFCs. We have focused on the effects of these contaminants on LSCF-GDC composite cathodes, as LSCF is still one of the most promising materials for intermediate and low-temperature SOFCs, but have also extensively investigated the effect of contaminants on LSM and LSM-YSZ composite cathodes. Experiments have been performed to investigate both the short-term (kinetic) and long-term (stability) influence of contaminants on cathode materials using electrochemical impedance spectroscopy (EIS) as the main tool. Post-mortem X-ray diffraction and electron microscopy was used to investigate irreversible changes that occurred in the samples. The results suggest that in the presence of different contaminants surface reaction kinetics on LSCF vary, and that the changes in kinetics correlate to the concentration of contaminants. In addition, applied bias shows a high impact on the interactions of contaminants with cathodes. Further, cross-contamination, such as air with H₂O+CO₂, increases overall polarization resistance of the cathode beyond exposure to a single contaminant. This study aims to elucidate mechanistic routes for contaminant degradation, and in doing so, provide information useful for the further development of reduced temperature SOFCs.