Bismuth ruthenate pyrochlore (Bi2Ru2O7:BRO) was tested as a cathode in several bismuth oxide-based electrolyte cells. Erbium oxide stabilized bismuth oxide (ESB) (Bi2O3)(0.8)(Er2O3)(0.2), Bi2V0.9Me0.1O5.35 (BIMEVOX10, Me = Co, Cu, Zn), and Bi2Ru2O7 (BRO) were synthesized via solid-state reaction. ESB and BIMEVOX powders were pressed and sintered into dense pellets while BRO was deposited and sintered as porous electrodes onto ESB and BIMEVOX dense pellet surfaces. Morphologies and phases of the materials were characterized by field emission scanning electron microscope and X-ray diffraction, respectively. Electrochemical performances of BRO/ESB and BRO/BIMEVOX symmetric cells were tested using electrochemical impedance spectroscopy at 200-700 degrees C in air. High polarization for BRO/BIMEVOX cells was observed. In contrast, BRO/ESB cells showed promising low polarization behavior. Different electrochemical performances of BRO electrodes, with ESB or BIMEVOX, indicated that the phases formed at the electrode/electrolyte interface dominated the cell polarization process for BRO/BIMEVOX cells. (c) 2006 The Electrochemical Society.