Tuning the oxygen vacancy concentration in a heterostructured electrode for high chemical and electrochemical stabilities

Thermally driven chemical instability at the perovskite electrode is one of the biggest challenges to overcome in the development of sustainable solid oxide fuel cells. At elevated temperatures, the A-site dopant (typically Sr) segregation toward the surface of the perovskite electrode induces the substantially nonstoichiometric surface with the formation of insulating Sr-rich phases by the electrostatic interactions between oxygen vacancies (V_o^∙∙) and doped Sr (Sr_La^'), deteriorating the oxygen reduction reaction kinetics. Herein, we report the precise tuning of the oxygen vacancy concentration at the perovskite surface in a Gd_0.1Ce_0.9O_2−δ (GDC)/La_0.6Sr_0.4CoO_3−δ (LSC) heterostructured electrode by rearranging the oxygen vacancies near the interface, resulting in an ∼15-fold increase in the surface exchange coefficient after long-term operation at 650 °C for 100 h. The depth profiles of the charged defects obtained by X-ray photoelectron spectroscopy revealed that the oxygen vacancy concentration at the perovskite surface can be controlled by the amount of vacancy acceptable sites in the GDC layer. This strongly affects the chemical and electrochemical stabilities after long-term operations. Our results demonstrate the potential of tuning the defect concentration in heterostructured electrodes to achieve highly sustainable electrodes for the long-term operations at elevated temperatures.