Electrochemical impedance spectroscopic characterization of impregnated La0.6Sr0.4Co0.2Fe0.8O3−δ cathode for intermediate-temperature SOFCs

The electrochemical performance of the impregnated La0.6Sr0.4Co0.2Fe0.8O3−δ-Y2O3 stabilized ZrO2 cathode (LSCF-YSZ) was studied with different amount of LSCF. Function as PO2, electrode resistance revealed that the rate-determining steps for oxygen reduction were changed with amount of LSCF loading. The rate-determining step is the charge transfer process for 12 wt% LSCF loading cathode. With the increasing amount of LSCF particles on the YSZ scaffold, the rate determining steps are the dissociation of oxygen molecules and adsorption-diffusion of oxygen atom for 20 wt% LSCF loading cathode. Accumulation of a great many LSCF particles on the YSZ scaffold makes the Knudsen diffusion of oxygen molecular of great importance for ORR. The rate-determining step is the Knudsen diffusion for 32 wt% LSCF loading cathode. The mean free path of oxygen molecules is about 0.22-0.27 μm at 1 atm and the temperature is between 600 and 800 °C. The appearance of inductive loop in the EIS for the cathode with high LSCF loading was possible influenced by the Knudsen diffusion process.