Unraveling the relationship between Sr stoichiometry in Sr_xFe_1.5Mo_0.5O_6−σ and its catalytic performance for high-temperature CO₂ electrolysis

The solid oxide electrolytic cell (SOEC) is one of the most promising energy conversion and storage devices, which could convert CO₂ to CO with high Faradaic efficiency and production rate. However, the lack of active and stable cathode materials impedes their practical applications. Here we focus on the promising perovskite oxide cathode material Sr₂Fe_1.5Mo_0.5O_6−σ, with the aim of understanding how A-atom stoichiometry and catalytic performance are linked. We find that increasing the strontium content in the perovskite improves the chemisorption of CO₂ on its surface, forming a SrCO₃ phase. This hinders the charge transfer and oxygen exchange processes. Simultaneously, strontoium segregation to the cathode surface facilitates coking of the surface during CO₂ electrolysis, which poisons the electrode. Consequently, a small number of Sr deficiencies are optimal for both electrochemical performance and long-term stability. Our results provide new insights for designing high-performance CO₂ electrolysis cathode materials.