Ultrathin defective Fe2O3−x skins on exsolved nanoparticles from a perovskite cathode enable highly active and sulfur-tolerant CO2 electroreduction

Abstract

Solid oxide electrolysis cells (SOECs) have emerged as a promising application for electrochemically converting CO₂ to CO, presenting a feasible strategy to mitigate industrial CO₂ emissions. Among various gas streams, blast furnace gas (BFG), a byproduct from steel making, contains high concentrations of CO₂ and impurities such as H₂S, which severely impact CO₂ conversion efficiency and cathode durability due to sulfur poisoning. Herein, a double perovskite system of Sr_1.6Pr_0.4Fe_1.35Ni_0.2Mo_0.45O_6−δ (SPFNM), functionalized with in situ exsolved FeNi₃ alloy nanoparticles (NPs) encapsulated by ultrathin Fe₂O_3−x layers via steam-assisted wet reduction (wet-SPFNM) was developed as a novel cathode for SOECs. This tailored FeNi₃/Fe₂O_3−x core–shell nanostructure provides additional oxygen vacancies for CO₂ electrolysis active sites and enhances sulfur tolerance, attributed to a defect-rich Fe₂O_3−x shell that effectively protects the metallic core by oxidizing adsorbed H₂S. A single cell with a wet-SPFNM cathode showed a current density of 568 mA cm⁻² at 1.3 V and 750 °C, approximately 38% higher than the conventional dry-reduced SPFNM (dry-SPFNM), containing exsolved metallic FeNi₃ alloy NPs. Furthermore, the wet-SPFNM cathode demonstrated excellent operational stability, showing negligible degradation over 100 h at 750 °C at a constant current of 250 mA cm⁻² under BFG conditions. This research highlights the potential of exsolved core–shell NPs as a robust design strategy for sulfur-tolerant SOEC cathodes operating in realistic industrial gas environments.