Electrochemical characterization of Co-doped Sr_0.8Ce_0.2MnO_3-δ cathodes on Sm_0.2Ce_0.8O_1.9-electrolyte for intermediate-temperature solid oxide fuel cells

Electrochemical properties of Co-doped Sr_0.8Ce_0.2MnO_3-δ cathode were investigated at the cathode/Sm_0.2Ce_0.8O_1.9 electrolyte interface. The electrochemical impedance spectroscopy was measured under applied cathodic voltages (E = -0.4 to 0 V). At E = 0 V, the area-specific resistance decreased from 2.20 Ω cm² to 0.19 Ω cm² at 700 °C with Co doping. Under the cathodic polarization, the rate determining step of oxygen reduction process was different for both cathodes: the charge transfer for Sr_0.8Ce_0.2MnO_3-δ and the diffusion process for Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3-δ. Besides, the overpotential also decreased from 124 mV to 19 mV at the current density of 0.1 A cm^-2 at 800 °C with Co doping. The improved electrochemical properties of Co-doped Sr_0.8Ce_0.2MnO_3-δ can be ascribed to the formation of more oxygen vacancies and more active sites for oxygen reduction reaction.