A High‐Entropy Layered Perovskite Coated with In Situ Exsolved Core‐Shell CuFe@FeO_x Nanoparticles for Efficient CO₂ Electrolysis

Abstract Solid oxide electrolysis cells (SOECs) are promising energy conversion devices capable of efficiently transforming CO₂ into CO, reducing CO₂ emissions, and alleviating the greenhouse effect. However, the development of a suitable cathode material remains a critical challenge. Here a new SOEC cathode is reported for CO₂ electrolysis consisting of high‐entropy Pr_0.8Sr_1.2(CuFe)_0.4Mo_0.2Mn_0.2Nb_0.2O_4‐δ (HE‐PSCFMMN) layered perovskite uniformly coated with in situ exsolved core‐shell structured CuFe alloy@FeO_x (CFA@FeO) nanoparticles. Single cells with the HE‐PSCFMMN‐CFA@FeO cathode exhibit a consistently high current density of 1.95 A cm⁻² for CO₂ reduction at 1.5 V while maintaining excellent stability for up to 200 h under 0.75 A cm⁻² at 800 °C in pure CO₂. In situ X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations confirm that the exsolution of CFA@FeO nanoparticles introduces additional oxygen vacancies within HE‐PSCFMMN substrate, acting as active reaction sites. More importantly, the abundant oxygen vacancies in FeO_x shell, in contrast to conventional in situ exsolved nanoparticles, enable the extension of the triple‐phase boundary (TPB), thereby enhancing the kinetics of CO₂ adsorption, dissociation, and reduction.