Design\nof a B‑Site\nCo-Free Multielement Perovskite\nOxide as Oxygen Electrode for Efficient CO<sub>2</sub> Solid Oxide\nElectrolysis Cells

The traditional oxygen electrode\nin solid oxide electrolysis\ncells\n(SOECs), (La,Sr)(Co,Fe)O<sub>3</sub> (LSCF), suffers from high cost,\nevaporation at high temperatures, and societal aspects of the use\nof Co. In this work, a Co-free B-site multielement (so-called high-entropy)\nperovskite oxide, La<sub>0.6</sub>Sr<sub>0.4</sub>Cu<sub>0.2</sub>Fe<sub>0.2</sub>Ti<sub>0.2</sub>Mn<sub>0.2</sub>Ni<sub>0.2</sub>O<sub>3‑δ</sub> (LSCuFTMN), has been synthesized and successfully\napplied as a novel oxygen electrode. X-ray photoelectron spectroscopy\n(XPS) data indicate that the multiple transition elements in the B-site\nexist in various valence states, leading to a spatially variable electron\nstructure. Electrochemical measurements of LSCuFTMN suggest that the\nmaterial exhibits extraordinary catalytic activity and stability under\nthe studied working atmospheres and a decrease in polarization resistance\nby 24% compared to LSCF. By distribution of relaxation time (DRT)\nanalysis, LSCuFTMN possesses better mass and charge transfer performance\nthan traditional LSCF. An SOEC with LSCuFTMN as the oxygen electrode\nhas been assembled and tested, and a current density of 1.2 A cm<sup>–2</sup> is obtained at 2.0 V and 800 °C in electrolysis\nof pure CO<sub>2</sub>, higher by nearly 50% compared to LSCF. The\nfaradaic efficiency is over 95%. No clear recession is observed in\nthe long term stability test. It is evident that multication –\nso-called high-entropy – oxides could be promising materials\nfor improving the working performance of SOECs.