In Situ Exsolution of Quaternary Alloy Nanoparticles for CO₂‐CO Mutual Conversion Using Reversible Solid Oxide Cells

Abstract Reversible solid oxide cell is a promising energy storage and conversion device for CO₂‐CO mutual conversion, with simplified cell configuration and performance stability. One key technical challenge is the lack of catalytically active and carbon‐tolerant fuel electrodes. The other one is still a lack of the kinetics mechanism and the redox stability of the active interface. Herein, the findings of a fuel electrode composed of a Sr₂Fe_1.0Co_0.2Ni_0.2Cu_0.2Mo_0.4O_6‐δ medium‐entropy perovskite matrix decorated with in situ exsolved Fe‐Co‐Ni‐Cu quaternary alloy nanoparticles (QA@SFO) are reported. Under a reducing atmosphere, the exsolution of the quaternary alloy is accompanied by a structural transformation from double perovskite to layered perovskite, forming an interface structure where alloy nanoparticles are strongly pinned to the substrate with abundant oxygen vacancies. Electrochemically, the highly active sites provided by the QA@SFO interface greatly enhance the kinetics of CO₂‐CO mutual conversion and exhibit outstanding durability for over 300 h at 1.3 V and 800 °C. Moreover, first‐principles calculations and ab initio molecular dynamics simulations from the atomic scale further elucidate the impressive electrocatalytic activity and stability and reveal that Fe and Ni in exsolved nanoparticles enhance the electrocatalytic activity, and the strong binding of Co and Cu to the parent improves the interfacial stability.