The cathode-electrolyte interface microstructure and surface overpotential are important factors to decide the oxygen reduction rate. Thus, the effects of the surface overpotential and temperature at the strontium- and iron-doped lanthanum cobaltite (LSCF)/gadoliniadoped ceria (GDC) electrode interface on yitria-stabilized zirconia (YSZ) have been analyzed by AC impedance. At low anodic overpotential near the equilibrium, the impedance diagram is characterized by a resistance with approximately a constant value of 0.078 Omega cm(2) at 1073 K. The resistance activation energy is 1.68 eV at zero applied overpotential. However, at high anodic overpotential such as 300 mV, the polarization resistance is significantly decreased with relatively low resistance activation energy of 1.33 eV. tinder cathodic overpotential, the observed behavior is similar to that under the anodic overpotential. At low cathodic overpotential, a high resistance value of 0.215 Omega cm(2) at 1073 K is obtained; whereas a high activation energy of 1.98 eV at -300 mV overpotential is estimated. in addition, both the resistance-overpotential curves at high anodic and cathodic overpotentials obey an exponential law. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.