Bismuth doped Sr₂Fe_1.5Mo_0.5O_6-δ double perovskite as a robust fuel electrode in ceramic oxide cells for direct CO₂ electrolysis

Electrochemical conversion of CO₂ to CO is an economically feasible method for mitigating greenhouse gas emissions. Among various electrochemical approaches, solid oxide electrolysis cells (SOECs) show high potential for CO₂ reduction reaction (CO₂-RR) due to their ability to operate at high temperatures, resulting in fast reaction kinetics and increased efficiency. Considering their main energy loss is still associated with the large overpotential at the fuel electrode, the development of the highly efficient and durable cathode for SOECs has been extensively searched after. Here, we propose an A-site doping strategy to enhance the properties of Sr₂Fe_1.5Mo_0.5O_6−δ (SFM), which improve its performance as a cathode in SOECs for CO₂-RR, demonstrating favorable activity and durability. The structural and physiochemical characterizations, together with DFT calculations, show that the partial replacement of Sr by Bi in the SFM double perovskite not only improves CO₂ adsorption capability at the catalyst surface but also enhances oxygen ionic conduction inside the bulk oxide, resulting in enhanced CO₂ electrocatalysis performance in SOECs. Specifically, a La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte-supported single cell with the new Bi-doped SFM cathode demonstrates a large current density of 1620 mA cm⁻² at a cell potential of 1.6 V at 850 °C with good operational stability up to 200 h. Bi-doped SFM thus represents a highly promising cathode for ceramic CO₂ electrolyzers and could accelerate our transition towards a carbon-neutral society.