Atomic‐Scale Engineering for New Generation Air Electrode Materials of Solid Oxide Cells: Quintuple Perovskite Sm2Ba3Co2Fe3O15‐δ with Twinned Crystal Structure

Abstract The catalytic activity and thermomechanical stability of electrode materials are crucial for the efficient operation of reversible solid oxide cell (rSOC). However, these two traits often impose limitations on one another. In this work, a unique quintuple perovskite Sm 2 Ba 3 Co 2 Fe 3 O 15‐δ (SBCF‐5L), comprising of A‐site ordered double perovskite layers and disordered simple perovskite layers, is reported as a high‐performance air electrode material for rSOC. The designed SBCF‐5L material exhibits a highly symmetrical tetragonal structure (pseudo‐cubic) with an isotropic thermal expansion and a limited chemical expansion. The formation barriers for oxygen vacancies are comparable between A‐site ordered layers and disordered simple perovskite layers, resulting in a high concentration of oxygen vacancies and 3D‐like bulk mobility of oxygen ions. Perpendicularly twinned nanodomains are developed in the particles, providing more active sites for surface electrode reaction. When applied in electrolyte‐supported cells, the SBCF‐5L electrode exhibits excellent electrochemical performance with low polarization resistance of 0.017 Ω cm −2 , high power density of 1.01 W cm −2 and high electrolysis current density of 1.08 A cm −2 at 1.3 V at 800 °C in fuel cell and electrolysis modes, respectively. This study introduces a new approach of atomic‐scale engineering to rationally design a new generation of air electrodes for rSOC.