Time dependences of the total and partial polarization resistances of Ni-cermet electrode with addition of Cu and impregnated with CeO2-delta in contact with the YSZ electrolyte in the reducing gas mixtures of different composition were studied by means of impedance spectroscopy at the temperature of 900 degrees C. In H-2 + H2O binary gas mixtures the degradation rate (decrease of electrochemical activity over time) of the Ni-cermet electrode increases sharply at the partial pressure of water over 45 vol.%. The degradation rate of the Ni-cermet electrode in the 10%CO + 90%CO2 gas mixture is significantly slower than in the 10%H-2 + 90%H2O gas mixture. The analysis of the impedance spectra showed that at the equilibrium potential the electrode reaction is limited by three stages. Major changes in the characteristics of the electrode during long exposures under working condition are associated with the changes ranger of the partial polarization resistances high- and middle-frequency. (C) 2013 Elsevier B.V. All rights reserved.