The effect of the substitution of Co for Cu in the intergrowth oxide La1.85Sr1.15Cu2-xCoxO6+delta on the crystal chemistry, thermal and electrical properties, and catalytic activity for oxygen reduction reaction (ORR) has been investigated to determine its viability as a cathode material for intermediate temperature solid oxide fuel cells (SOFCs). The larger size and preference for higher oxygen-coordination number of the La3+/Sr2+ ions allow intercalation of excess oxygen between the two CuO2 layers, and vacancies are introduced into the O(1) sites of the CuO2 planes. The La1.85Sr1.15Cu2-xCoxO6+delta oxides show thermal expansion coefficients (TEC) of similar to 15 x 10(-6) degrees C-1 that are compatible with that of the Gd0.2Ce0.8O1.9 (GDC) electrolyte in SOFC. Fuel cell data collected with electrolyte-supported and anode-supported single cells reveal that the La1.85Sr1.15Cu2-xCoxO6+delta + GDC (50:50 vol.%) composite cathodes exhibit lower polarization resistance compared to the pure La1.85Sr1.15Cu2-xCoxO6+delta cathodes due to the extended triple phase boundary (TPB) where the ORR occurs. Among the various cathode compositions investigated in this study, the La1.85Sr1.15Cu1.8Co0.2O6.26 + GDC composite was found to be optimal with the lowest polarization loss. (C) 2012 Elsevier Ltd. All rights reserved.