Double substituted Co-free perovskite oxides for quasi-symmetric reversible solid oxide cells (rSOCs)

High-temperature CO₂ electrolysis in solid oxide electrochemical cells offers one of the most efficient routes for carbon dioxide conversion, enabling the production of highly pure carbon monoxide due to favorable thermodynamics and fast kinetics above 600 °C. The emergence of CO:CO2 reversible solid oxide cells (rSOCs) further enhances system efficiency, promoting integration with CO₂-rich and CO-rich industrial exhaust streams. However, reversible operation imposes stringent requirements on electrode materials, which must combine high catalytic activity, redox stability, and long-term durability under a wide range of oxygen partial pressures. Herein, we report a doubly B-site–substituted perovskite, La₀.₆Sr₀.₄Fe₀.₆Mn₀.₂M₀.₂O₃−δ (M = Cu, Ni), as a multifunctional electrode platform for rSOCs. Both La₀.₆Sr₀.₄Fe₀.₆Mn₀.₂Cu₀.₂O₃−δ (LSFMC) and La₀.₆Sr₀.₄Fe₀.₆Mn₀.₂Ni₀.₂O₃−δ (LSFMN) are synthesized as single-phase perovskites, with rhombohedral symmetry (R-3c). When evaluated as oxygen electrodes in symmetric cell configurations, LSFMC and LSFMN exhibit significantly enhanced oxygen electrocatalysis, achieving a decrease in area-specific resistance by 51% and 38%, respectively, compared to the unsubstituted material. Under reducing conditions, LSFMN undergoes controlled and homogeneous exsolution of Fe-Ni nanoparticles, generating catalytically active metallic domains while preserving structural integrity. A quasi-symmetric electrolyte-supported cell based on La₀.₈Sr₀.₂Ga₀.₈Mg₀.₂O₃−δ (LSGM) electrolyte, employing LSFMN as fuel electrode and LSFMC as air electrode, demonstrates excellent performance and durability in both CO-fuelled solid oxide fuel cell mode and CO₂ electrolysis mode. Stable and reversible operation is maintained for over 150 h in a 50:50 CO:CO2 mixture. Targeted B-site substitution of Mn-stabilized ferrites enables the design of high-performance, cobalt-free and reversible electrodes, offering a promising strategy for next-generation rSOCs.