Electrochemical oxygen reduction behavior for a half cell composed of a mixed ionic and electronic conducting (MIEC) oxide and an oxygen excess-type solid electrolyte was investigated. A perovskite-type MIEC oxide, (La0.6Sr0.4)(Co1-yFey)O3-delta (LSCF), was employed as a base material for an electrode catalyst of oxygen reduction reaction. As an electrolyte, Al-doped lanthanum silicate [La-10(Si5.8Al0.2)O-26.9 (ALSO)] was used, which is a new class of oxide ion conductors with apatite-type structure. The evaluated polarization resistance, R-pol, for the reaction largely depended on y, and the minimum resistance was obtained for y = 0.2. The R-pol value was 0.3 Omega cm(2) at 1073 K in ambient air [P(O-2) = 2.1 x 10(4) Pa] for y = 0.2. To improve the performance, introduction of silver nano-particles onto the LSCF particles was studied. With the Ag-modification, R-pol at 1073 K could be minimized toward 0.08 Omega cm(2). The cathodic overpotential of the electrode evaluated from DC polarization at 1073 K was 18 mV at 0.1 A cm(-2). (C) 2012 Elsevier B.V. All rights reserved.