High-entropy approach to double perovskite cathode materials for solid oxide fuel cells: Is multicomponent occupancy in (La,Pr,Nd,Sm,Gd) BaCo2O5+delta affecting physicochemical and electrocatalytic properties?

High-entropy (La,Pr,Nd,Sm,Gd)BaCo2O5+delta double perovskite-type oxide having an equimolar, high-entropy, A-site-layered arrangement of cations is synthesized for the first time. A modified Pechini method, followed by calcination and sintering at 1,100 degrees Chelps in obtaining a single-phase, homogenousmaterialwith tetragonal I4/ mmm symmetry. In situ X-ray diffraction and dilatometric studies show excellent phase stability up to 1,100 degrees Cin air, with the average thermal expansion coefficient of 23.7.10(-6) K-1 within the 25-1,100 degrees C range. Total electrical conductivity of the metallic character exceeds 1,600 S cm(-1) at room temperature. Equilibrated oxygen content at room temperature is determined as 5.69. The cathodic polarization resistance of the (La,Pr,Nd,Sm,Gd)BaCo2O5+delta layers, manufactured on the La0.8Sr0.2Ga0.8Mg0.2O2.8 (LSGM) solid electrolyte of proved inertness, is as low as 0.037 Omega cm(2) at 900 degrees C, and 0.175 Omega cm(2) at 750 degrees C. The determined value of the power density in the LSGM-based, electrolyte-supported (thickness ca. 200 mu m) fuel cell reaches 857mWcm(-2). These results indicate possible applicability of the developed cathode material for solid oxide fuel cells, making it also one of the best-performing high-entropy air electrodes reported until now. However, the determined physiochemical characteristics of thematerial indicate a relatively limited influence of the high-entropy A-site arrangement in comparison to the conventional analogs, including the synthesized Nd0.88Sm0.12Co2O5+delta composition, characterized by the same effective radius of the lanthanide cations.