Impedance spectroscopy was used to study the electrochemical performance of pure and ion-impregnated La0.7Sr0.3MnO3 (LSM) cathodes on YSZ (Y2O3-stabilized ZrO2) electrolytes in single chamber fuel cell conditions, i.e. a mixture gas with oxygen as oxidant, methane as fuel and nitrogen as dilute gas. Measurements were taken at the furnace temperature range of 550-750 degrees C and the CH4/O-2 ratios from 1 to 2. Polarization resistances (R-p) for pure and impregnated LSM cathodes increased obviously as the CH4/O-2 ratio increased at 650-750 degrees C. Polarization resistances of Sm0.2Ce0.8O1.9 (SDC) impregnated LSM cathode were much smaller than the ones of pure LSM cathode under the same conditions. Overtemperatures were occurred at both cathodes due to the partial oxidation of methane. (C) 2009 Elsevier Ltd. All rights reserved.