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 Ba_1–xK_xCo_0.5Fe_0.4Nb_0.1O_3−δ (B_1–xK_xCFNb) perovskite cathodes with superior CO₂ adsorption performance for direct CO₂ electrolysis in SOECs. An introduction of 10% potassium in BaCo_0.5Fe_0.4Nb_0.1O_3−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 Ba_0.9K_0.1Co_0.5Fe_0.4Nb_0.1O_3−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.