Novel High‐Entropy Air Electrodes Enhancing Electrochemical Performances of Reversible Protonic Ceramic Cells

Abstract Reversible protonic ceramic cells (R‐PCCs) have been in the spotlight as prominent electrochemical devices for green hydrogen production and utilization. The design of efficient air electrodes is critical for enhancing cell performances, requiring high hydration ability, excellent catalytic activities, and appropriate thermal expansion coefficients (TEC). Herein, novel high‐entropy oxides La(Co_0.2Cu_0.2Fe_0.2Ni_0.2Me_0.2)O_3–δ (Me = Al, Mn, Cr) featuring five cations at B‐site of ABO₃ perovskite are presented. La(Co_0.2Cu_0.2Fe_0.2Ni_0.2Cr_0.2)O_3–δ (LCCFN‐Cr) catalyst exhibits the best proton incorporation ability and catalytic activities among three oxides, concluded by analyzing the oxygen vacancy concentration and the chemical bond information. Moreover, the high‐entropy effect at B‐site reduced the TEC of this Co‐contained oxide to a modest extent through large‐ratio substitution of Co by other cations. When applied as an air electrode, the BaZr_0.6Ce_0.2Y_0.1Yb_0.1O_3–δ electrolyte‐based R‐PCCs yielded a high current density of 2.14 A cm⁻² and a peak power density of 0.60 W cm⁻², with an extremely low polarization resistance of 0.05 Ω cm² at 650 °C. These findings not only provide a novel air electrode for R‐PCCs, but also demonstrate a pathway to design effective oxide catalysts for other energy conversion devices by integrating the advantages of Co and high‐entropy effect.