Tailoring the properties of cathode is of great importance to improve the performance of proton-conducting solid oxide fuel cells (SOFC-H). This work demonstrates that the performance of BaCe0.40Sm0.20Fe0.40O3-delta cathode can be optimized by introducing appropriate amount of Co3O4. The 5-10 wt% Co3O4 reacts with BaCe0.40Sm0.20Fe0.40O3-delta, forming conductive mixed oxygen ionic-electronic phases. The materials with 5-10 wt% Co3O4 exhibits protonic and improved oxygen ionic-electronic conductivity in wet air, which contributes greatly to the electrocatalytic activity toward the reaction on the cathode. The (95-90%) BaCe0.40Sm0.20Fe0.40O3-delta (5-10%) Co3O4 demonstrates lower ASR, lower cathode overpotential, higher exchange current density, and higher peak power density. Higher content of Co3O4 (20%) will result in the disappearance of protonic conducting phase and denser electrode microstructure, which are detrimental to the performance. This work demonstrates that designing cathode materials with modified microstructure, which is simultaneously protonic, oxygen ionic and electronic conductive, is crucial to improve the performance of SOFC-H. (C) 2013 Elsevier Ltd. All rights reserved.