Bismuth ruthenate and erbia-stabilized bismuth oxide (ESB) composites were studied as prospective cathode materials for solid oxide fuel cells (SOFCs) operating at intermediate temperatures (IT). Phase chemistry between bismuth ruthenate and ESB was studied using differential thermal analysis and X- ray diffraction (XRD). Symmetrical cells were fabricated on gadoliniumdoped ceria electrolytes and studied by electrochemical impedance spectroscopy. Bi2Ru2O7-ESB composite electrodes showed area specific resistance values significantly lower than single-phase bismuth ruthenate electrodes, with the best performance from composite electrodes containing 31.25-43.75 wt % ESB. At 700 degrees C, composite electrodes containing 31.25-43.75 wt % ESB exhibited an area specified resistance of 0.08-0.11 Omega cm(2) as compared to 1.78 Omega cm(2) for Bi2Ru2O7. Introduction of the ESB phase reduced the rate limiting charge transfer and surface-diffusion steps in the oxygen reduction reaction, resulting in improved electrode performance. (c) 2007 The Electrochemical Society.