In-Situ Removal of Sr Segregation via Surface Construction to Engineer Highly Active Oxygen Electrode for Low-Temperature Solid Oxide Electrochemical Cells Operating below 500 °C

Recent advancements in solid oxide electrochemical cells (SOCs) heavily depend on the development of active and stable oxygen electrodes that exhibit superior activity and stability for oxygen reduction and evolution reactions at low temperatures. Here, we report a new surface-constructed oxygen electrode, Sr(Mg,Ti,Fe)O3–δ coated with Co3O4 (SMTF–Co3O4), designed to operate below 500 °C for low-temperature SOCs. The electrode electrochemical performance is primarily improved by the in situ reaction of Co3O4 with surface-segregated SrO, forming SrCoO3 and Co3O4/SrCoO3/SMTF heterointerfaces, which significantly enhances the surface oxygen adsorption capacity. The SMTF–Co3O4 electrode demonstrates a remarkably low reaction activation energy of ∼0.56 eV, with electrode polarization resistance as low as 0.56 Ω cm2 at 450 °C. The full cell, incorporating a thin scandia-stabilized zirconia (ScSz) electrolyte (∼3 μm) and the SMTF–Co3O4 oxygen electrode, reaches maximum power density and electrolysis current density (at 1.3 V) of 0.6 W/cm2 and 0.44 A/cm2, respectively, at 500 °C. Especially, 5–8 times enhancement in the cell performance at 450 °C is achieved by SMTF with the surface construction compared to the pristine electrode. Furthermore, the SMTF–Co3O4 electrode maintains stable performance in both fuel cell and electrolysis modes.