New cathode materials with high performance are required to realize efficient solid oxide fuel cells (SOFCs) operating at intermediate temperatures (IT) of 500-700 degrees C. Bismuth ruthenate is known to be catalytically active toward oxygen reduction and to have high electronic conductivity (similar to 300 S/cm) in the temperature range of interest, making it a prospective cathode material for IT-SOFCs. In this work, the performance of bismuth ruthenate pyrochlore (Bi2Ru2O7) electrodes was studied using impedance spectroscopy. Symmetrical cells were fabricated on gadolinium-doped ceria electrolytes and studied as a function of oxygen partial pressure in the temperature range 400-700 degrees C. Bismuth ruthenate electrodes showed an area specific resistance (ASR) of 1.45 Omega cm(2) at 700 degrees C and 55.64 Omega cm(2) at 500 degrees C in air. The change in ASR with oxygen partial pressure suggests that the rate-limiting step for oxygen reduction is the surface diffusion of dissociatively adsorbed oxygen at the electrode surface to the triple-phase boundaries. (c) 2005 The Electrochemical Society.