Cubic perovskite oxide La0.5Ba0.5CoO3-delta (LBCO) and its composite with Gd0.1Ce0.9O1.95 (GDC) electrolyte, LBCO-GDC in 1:1 weight ratio were prepared. Chemical compatibility between LBCO and GDC was studied and no serious phase reaction occurred at temperatures up to 1050 degrees C in air. Electrochemical performance of the cathodes was measured by Electrochemical Impedance Spectroscopy (EIS) as a function of temperature and oxygen partial pressure. Electrode reaction mechanism was analyzed based on fitting results of the EIS with proper equivalent circuit models. Comparison of the results demonstrated that introduction of the ionic conductive GDC component to the LBCO-GDC composite cathode hardly influenced gas diffusion through bulk of the cathode (low-frequency process) while greatly enhanced oxygen ionic transfer across the cathode/electrolyte interface (high-frequency process) and the electrode reaction occurring in the medium-frequency range. As a result, the LBCO-GDC composite cathode exhibited lower area-specific resistance (ASR) than the LBCO cathode, with ASR value ranging from similar to 0.12 Omega cm(2) at 600 degrees C to similar to 0.01 Omega cm(2) at 800 degrees C. These results have demonstrated that the LBCO-GDC composite (1:1 weight ratio) is highly promising as a cathode for intermediate temperature solid oxide fuel cell. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.