Innovative Approach to Design SOFC Air Electrode Materials: High Entropy La1-xSrx(Co,Cr,Fe,Mn,Ni)O3-δ (x = 0, 0.1, 0.2, 0.3) Perovskites Synthesized by the Sol-gel Method

Among reported for the first time Cr-containing high entropy La1-xSrx(Co,Cr,Fe,Mn,Ni)O3-δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) perovskite-type oxides, the selected Sr-doped La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3-δ material is documented to possess attractive properties as a candidate air electrode material for Solid Oxide Fuel Cells (SOFC). Nanosized powders of the considered oxides are obtained using the modified Pechini sol-gel method. In the formed solid solution with a simple perovskite structure the strontium solubility limit is found to be at least x = 0.3. Room temperature (RT) structural data indicate the presence of the rhombohedral structural distortion (R-3c symmetry) in the materials. The high-temperature structural studies for selected La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3-δ indicate the occurance of a phase transition to the aristotype Pm-3m structure occurring at ca. 800 °C. Linear thermal expansion coefficient in RT-1000 °C range is found to be moderate, 16.0(3)·10-6 K-1. Results of impedance spectroscopy measurements support the semiconducting-type behavior of the electrical conductivity for all single-phase materials, in a temperature range of RT-1000 °C. The maximum recorded conductivity for La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3-δ composition exceeds 16 S·cm-1 in 900-1000 °C range, being suitable for the application. Furthermore, chemical stability toward the La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte is proven. Considering the presence of chromium, typically deleterious for the performance, the measured value of the total cathodic polarization resistance for La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3-δ-based electrode, being 0.126 Ω·cm-2 at 900 °C, seems to be very attractive. The results obtained for the button-type fuel cell indicate power densities at the level of 550 mW cm-2 at 900 °C. Therefore, it can be considered that the high entropy-based approach enables proposing alternative SOFC air electrode materials, with otherwise inaccessible chemical compositions.