Oxygen reduction performance of F-doped La_1−xSr_xCo_1−yFe_yO_3−δ solid oxide fuel cells cathode

Solid oxide fuel cells (SOFCs), which are electrochemical devices that generate power with high efficiency, free of pollution, and nonregional restrictions, have attracted extensive attention. A traditional SOFC works at temperatures more than 800 °C, which introduces several severe problems or drawbacks, such as the high possibility of interfacial reaction between the cell components, easy densification of the electrode layer, possible crack formation owing to mismatch in the thermal expansion of cell components, and the requirement for a high-cost LaCrO₃ ceramic as the interconnect material. Thus, reducing the operating temperature of SOFCs has become a consensus among researchers for the benefit of long-time operation. On the other hand, the operation of SOFCs at lower temperatures introduces several major issues, such as the increase in electrode resistivities and polarization losses of electrode reactions, particularly the oxygen reduction reaction in the cathode. Presently, perovskite-based oxides with mixed ion-electron conductivity (MIEC) are the most promising cathode materials for intermediate temperature SOFCs. Among the various mixed conducting oxides, cobalt-containing ones usually show excellent ionic conductivity and catalytic activity for oxygen reduction, and therefore, have received particular attention recently. La_1−xSr_xCo_1−yFe_yO_3−δ(LSCF) is a candidate of SOFC cathodes working below 800 °C, considering its high oxygen reduction reaction activity together with its mixed ionic electronic conducting property. Meanwhile, many experimental results pointed out that doping an F anion into the perovskite cathode can improve its electrochemical performance and stability in addition to the conventional A- and B-site doping. To study the oxygen reduction reaction process of the F-doped perovskite cathode, the electronic structure, oxygen absorption on the (100) surface, the formation energy of oxygen vacancy, and activation energies for oxygen ion migration in the bulk F-doped LSCF were calculated based on the density functional theory. The results reveal that doping F in the LSCF can improve oxygen absorption and oxygen ion migration, further promoting the activity of the cathode.