An improved oxygen reduction reaction activity and CO₂-tolerance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ achieved by a surface modification with barium cobaltite coatings

Solid oxide fuel cells (SOFCs) cathode often suffers from the poisoning effect of the contaminants commonly encountered in air such as CO₂. Here we report an effective approach to enhancing the activity and CO₂ tolerance of the state-of-the-art La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathode enabled by a coating of BaCoO_3-δ (BCO), as verified by the electrochemical testings, Raman analyses, and density functional theory calculations. When surface modified with a thin-film BCO coating, LSCF displays a much enhanced ORR activity and an improved durability against CO₂. For example, anode supported SOFCs with the LSCF cathode coated with BCO coatings show a remarkable peak power density (P_max) of 0.41 Wcm⁻² and a significantly reduced degradation rate in current density of ∼0.08%h⁻¹ at 0.8 V and 700 °C for a period of 300 hs when humidified H₂ (with 3 vol%H₂O) was used as fuel and air with 8 vol% CO₂ as oxidant. The demonstrated performance is improved when compared with those of the cells with a blank LSCF electrode (a P_max of ∼0.36 Wcm⁻² and a degradation rate of ∼0.15%h⁻¹) under the same conditions. The adsorption energy calculations suggests that BCO coating makes CO₂ adsorption much weaker than LSCF (−0.54 eV versus −1.07 eV).