A highly active, CO₂-tolerant electrode for the oxygen reduction reaction

One challenge facing the development of high-performance cathodes for solid oxide fuel cells (SOFC) is the fast degradation rate of cathodes due to poisoning by contaminants commonly encountered in ambient air such as CO₂. Here we report a double perovskite PrBa_0.8Ca_0.2Co₂O_5+δ (PBCC) cathode with excellent ORR activity and remarkable CO₂ tolerance under realistic operation conditions. When tested in a symmetrical cell in air with ∼1 vol% CO₂ at 750 °C, the PBCC electrode shows an area specific resistance of ∼0.024 Ω cm², which increases to 0.028 Ω cm² after 1000 h operation. The degradation rate is ∼1/24 of that of the state-of-the-art La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) cathode under the same conditions. Impedance spectroscopy and in situ surface enhanced Raman spectroscopy analyses indicate that the surface of the PBCC electrode is much more active for oxygen exchange and more robust against CO₂ than that of LSCF, as confirmed by density functional theory calculations. The fast ORR kinetics and excellent durability of PBCC in air with CO₂ highlight the potential of PBCC as a highly promising material for devices involving oxygen electrochemistry such as solid oxide fuel cells, electrolysis cells, or gas separation membranes.