One of the main problems for the deployment of intermediate-temperature solid oxide fuel cells (IT-SOFCs) is their chemical stability, since most of SOFCs contain alkaline-earth metal elements (Ba, Sr and Ca) that easily react with CO₂ forming carbonates. To tackle this problem, we performed a systematic investigation of a series of Ni_0.7Co_0.3O–Ce_0.8Sm_0.2O_1.9 (NC3O-SDC) composite cathodes, which are CO₂-stable and alkaline-earth-free compounds. In this work, NC3O-xSDC (with x = 0-60 wt.%) were synthesized by self-propagating combustion method and investigated as new cathode materials for oxygen-ion conducting SOFCs. The thermal stability and phase structure of NC3O polycrystalline powders were studied using TG-DTA and XRD analysis, which confirmed that NC3O is chemically compatible with SDC. The electrical conductivity and thermal expansion of the NC3O-xSDC samples were measured. The electrochemical properties of NC3O-xSDC/SDC/NC3O-xSDC cells were studied using electrochemical impedance spectroscopy measurements. Among the NC3O-xSDC series, NC3O-30SDC showed a minimum in cathode polarization resistance, being 0.071 Ωcm² at 800. A maximum power density of 200 mWcm^-2 at 600 was obtained using anode-supported SOFCs.