The mixed ionic and electronic conductors of La0.9Ca0.1Ni0.5Co0.5O3–Ce0.8Sm0.2O1.9 (LCNC–SDC) are investigated systematically for potential application as a cathode for solid oxide fuel cells based on a Ce0.8Sm0.2O1.9 (SDC) electrolyte. The electrochemical impedance spectroscopy (EIS) measurements are performed in air over the temperature range of 600–850 °C to determine the cathode polarization resistance. The exchange current densities for oxygen reduction reaction (ORR), determined from the low-field cyclic voltammetry, high-field cyclic voltammetry, and EIS data are systematically investigated. The activation energies (Ea) for ORR determined from the slope of Arrhenius plots are in the range of 102.33–150.73 kJ mol−1 for LCNC–SDC composite cathodes. The experimental results found that LCNC–SDC (70:30) composite cathode has a maximum exchange current density and a minimum polarization resistance of 0.30 Ω cm2 for 850 °C among LCNC–SDC composite cathodes.