The effects and affecting mechanisms of carbon dioxide on oxygen reduction reactions on the La0.6Sr0.4CoO3-delta (LSC) and La0.8Sr0.2MnO3+delta (LSM) cathodes have been investigated. The presence of CO2 in O-2 flow reduces the LSC and LSM cell performance and increases polarization resistance. CO2 impedes oxygen dissociative adsorption on the LSC cathode, whereas CO2 inhibits dissociation of adsorbed oxygen molecule or diffusion of O-species on the LSM cathode. CO2 adsorption on the LSC cathode obeys Temkin model in 550-650 degrees C and Freundlich model in 700-800 degrees C. Different CO2 adsorption behaviors are ascribed to the change in LSC structure and the change in oxygen reduction mechanism. CO2 adsorption on the LSM cathode obeys Freundlich model in 650-800 degrees C. The differences in the effects and affecting mechanisms of CO2 on LSM and LSC are related to their differences in composition and structure. (C) 2012 Elsevier By. All rights reserved.