The process of oxygen reduction at an interface metallic microelectrode solid oxide electrolyte was investigated at 700 degrees C under various oxygen partial pressures. In these experimental conditions, an increase of absolute current was observed when the electrodes made of Pt, Ag and Au were polarized with negatives overpotential down to -0.3 V. Such an unusual behaviour was explained by the increase of the three-phase boundary length due to the deposition and subsequent reduction of metal oxides in the vicinity of Pt and Ag electrodes. However, in the case of Au electrode, no pattern of migrated metal was observed around the electrode. In this case, the occurrence of autocatalytic electrode reaction is suggested to explain the phenomenon. (C) 2011 Elsevier B.V. All rights reserved.