Design of a B-Site Co-Free Multielement Perovskite Oxide as Oxygen Electrode for Efficient CO2 Solid Oxide Electrolysis Cells

The traditional oxygen electrode in solid oxide electrolysis cells (SOECs), (La,Sr)(Co,Fe)O₃ (LSCF), suffers from high cost, evaporation at high temperatures, and societal aspects of the use of Co. In this work, a Co-free B-site multielement (so-called high-entropy) perovskite oxide, La_0.6Sr_0.4Cu_0.2Fe_0.2Ti_0.2Mn_0.2Ni_0.2O_3-δ (LSCuFTMN), has been synthesized and successfully applied as a novel oxygen electrode. X-ray photoelectron spectroscopy (XPS) data indicate that the multiple transition elements in the B-site exist in various valence states, leading to a spatially variable electron structure. Electrochemical measurements of LSCuFTMN suggest that the material exhibits extraordinary catalytic activity and stability under the studied working atmospheres and a decrease in polarization resistance by 24% compared to LSCF. By distribution of relaxation time (DRT) analysis, LSCuFTMN possesses better mass and charge transfer performance than traditional LSCF. An SOEC with LSCuFTMN as the oxygen electrode has been assembled and tested, and a current density of 1.2 A cm^–2 is obtained at 2.0 V and 800 °C in electrolysis of pure CO₂, higher by nearly 50% compared to LSCF. The faradaic efficiency is over 95%. No clear recession is observed in the long term stability test. It is evident that multication – so-called high-entropy – oxides could be promising materials for improving the working performance of SOECs.