Robust Cathode for Efficient CO ₂ Electrolysis Driven by FeO ₆ Octahedral Rotation and Jahn–Teller Distortion in Solid Oxide Electrolysis Cells

It is well-established that even minor modulation of the BO₆ octahedra within perovskite structures can induce significant variations in material functionalities, suggesting that controlling the degree of octahedral distortion in perovskite architectures represents a promising approach to further enhance the electrocatalytic performance and stability of perovskite-based electrocatalysts. In this study, a composite perovskite cathode (Sr₂Fe_1.54Mo_0.46O_6-δ+SrMoO₄) for solid oxide electrolysis cells was synthesized using a sintering-free self-assembly method. Comprehensive characterizations and density functional theory calculations reveal that the Sr₂Fe_1.54Mo_0.46O_6-δ perovskite undergoes octahedral rotations, and the increase in Fe⁴⁺ (<i>t</i>_<i>2g</i>³_<i>eg</i>¹) is accompanied by asymmetric electron occupation within degenerate orbitals, inducing Jahn-Teller distortion in FeO₆ octahedra. These octahedral deformations modulate the coordination environment of the Fe-site, with their optimized spatial orientation of orbitals effectively capturing intermediates linked to surface-adsorbate bonds. This enhances metal-oxygen hybridization and shifts the O <i>2p</i> band center toward the Fermi level, facilitating oxygen vacancy formation and improving the CO₂ adsorption capability. Consequently, these features enable a current density of 1.58 A cm^-2 at 800 °C and 1.5 V, significantly outperforming the idealized Sr₂Fe_1.5Mo_0.5O_6-δ-based system (0.87 A cm^-2) under the same conditions. This work elucidates the influence of FeO₆ octahedral distortion on high-temperature CO₂ reduction reaction performance and its underlying mechanisms and proposes a straightforward method for the design of solid oxide cell electrocatalysts.