Modulating Oxygen Activity via Cation Doping for Efficient High-Temperature Carbon Dioxide Electrolysis

High-temperature solid oxide electrolysis cells (SOECs) offer a promising pathway for CO₂-to-CO conversion yet are hindered by cathode inactivity. This study demonstrates cation doping in Sr₂Ti_0.8Fe_1.2O_6-δ (STF), specifically forming Sr₂Ti_0.8FeNi_0.2O_6-δ (STFN) and Sr₂Ti_0.8FeCo_0.2O_6-δ (STFC), as an effective strategy for modulating oxygen activity and enhancing CO₂ electrolysis performance. The STFC cathode delivers optimal results, achieving a 1.15 A cm^-2 current density, 8.01 mL min^-1 cm^-2 CO production rate, and >99% Faradaic efficiency at 1.6 V and 800 °C. Advanced spectroscopic techniques combined with density functional theory calculations reveal that Co doping increases oxygen activity, evidenced by an upshifted O 2p band center and reduced oxygen vacancy formation energy. Consequently, CO₂ adsorption for carbonate (CO₃^2-) intermediate formation is facilitated, and the energy barrier for CO generation is reduced. A techno-economic assessment projects a competitive CO production cost of $748 per ton. These insights provide fundamental guidelines for the design of high-activity catalysts in high-temperature electrochemical systems.