In silico design and experimental validation of a high-entropy perovskite oxide for SOFC cathodes

Abstract

High entropy perovskite oxides have the potential to significantly enhance electrode performance in solid oxide fuel cells (SOFCs) and batteries. However, not all high entropy configurations yield single-phase perovskite oxides. This study focuses on screening La_0.2Sr_0.2A_0.2B_0.2C_0.2MnO₃ (where A/B/C = Pr, Gd, Nd, Ba, and Ca) for oxygen reduction reaction electrocatalyst applications. Possible configurations are analyzed by evaluating the tolerance factor based on ionic radii and oxidation states, and enthalpy of mixing. Considering these, La_0.2Sr_0.2Ca_0.2Gd_0.2Pr_0.2MnO₃ (LSCGP) is identified as a synthesizable high entropy perovskite oxide, which is experimentally synthesized. In Sr containing perovskites, Sr is known to segregate to the surface. Hence, LSCGP is first assessed for Sr-cation segregation using density functional theory (DFT), molecular dynamics (MD), and X-ray photoelectron spectroscopy (XPS). The results indicate negligible Sr-cation segregation towards the surface. DFT calculations show oxygen vacancy formation is facilitated in LSCGP compared to the other high entropy perovskite oxide such as La_0.2Sr_0.2Ba_0.2Nd_0.2Pr_0.2MnO₃ (LSBNP), and simple perovskites such as La_0.8Sr_0.2MnO₃ (LSM20) and La_0.5Sr_0.5MnO₃ (LSM50). MD studies further demonstrate that LSCGP exhibits significantly higher oxygen anion diffusivity compared to LSM20, LSM50, and LSBNP. Electrochemical performance of LSCGP electrode is characterized in a symmetric cell and SOFC configurations. In the symmetric cell, LSCGP showed significantly reduced polarization resistance at the OCV, as compared to the similarly fabricated LSM. The high surface stability and enhanced electrocatalytic properties of LSCGP present it as a promising candidate for electrode applications in energy storage and conversion devices.