Active Potassium-Doped Perovskite Cathodes with High Oxygen Defects for High-Temperature CO₂ Electrolysis

Solid oxide electrolysis cells (SOECs) can efficiently electrolyze CO2 into CO to alleviate environmental pollution caused by greenhouse gas emissions. However, their practical applications are limited by insufficient CO2 reduction reaction (CO2RR) performance of the cathode materials. In this study, we explored a series of potassium-doped Ba1–xKxCo0.5Fe0.4Nb0.1O3−δ (B1–xKxCFNb) perovskite cathodes with superior CO2 adsorption performance for direct CO2 electrolysis in SOECs. An introduction of 10% potassium in BaCo0.5Fe0.4Nb0.1O3−δ resulted in a substantial increase in oxygen vacancies from 0.316 to 0.423 at 800 °C. The electrical conductivity relaxation test further verified that the oxygen defects improve the surface-exchange coefficient of oxygen for Ba0.9K0.1Co0.5Fe0.4Nb0.1O3−δ (B90K10CFNb). The increased surface-exchange kinetics with more oxygen defects and CO2 adsorption capacity with high-alkalinity potassium considerably accelerated the CO2RR processes on the cathode of SOECs. The current density of the electrolysis cell with the B90K10CFNb cathode reaches 0.588 A cm–2 under 1.5 V at 800 °C, which is 3% higher than that of its BCFNb counterpart. Moreover, the B90K10CFNb electrolysis cell remained stable for 100 h under 1.5 V at 800 °C. This study underscores the potential of regulating oxygen defects in perovskite cathode materials through alkali metal cations for high-temperature CO2 electrolysis.