Ruddlesden–Popper oxide SrEu2Fe2O7 as a promising symmetrical electrode for pure CO2 electrolysis

Abstract

Nowadays, effective utilization of CO₂ has been a worldwide issue. Among numerous CO₂ conversion devices, solid oxide electrolysis cells (SOECs) have drawn special attention due to their high energy conversion efficiency, great potential in carbon cycling, and low environmental impacts. Compared with the typical ones taking asymmetrical configuration, symmetrical SOECs adapting the same oxide materials as both the cathode and anode have the advantages of simplified fabrication procedures, reduced processing costs and minimized compatibility issues. As the appropriate sites for CO₂ conversion, cathodes play the key role in determining the performance of symmetrical SOECs, and thus, attract more attention to improve their electrocatalytic behaviors and endurance via exploring novel materials. In this work, Eu-doped Ruddlesden–Popper (R–P) oxide, SrEu₂Fe₂O₇ (SEF), is applied as an electrode material for symmetrical SOECs to directly electrolyze pure CO₂. The outstanding structural stability and excellent electrochemical activity of the SEF electrode under both oxidizing and reducing atmospheres are demonstrated, and relatively low polarization resistances of 0.07 Ω cm² in air and 0.48 Ω cm² in 2CO₂–CO mixtures at 800 °C are observed. A great current density of 1.27 A cm⁻² at an applied voltage of 1.5 V and 800 °C is achieved on this symmetrical SOEC. An extremely low polarization resistance of 0.27 Ω cm² is also observed under open circuit conditions. Further, the symmetrical button cell has demonstrated excellent stability within 260 h of the long-term CO₂ electrolysis test.