An 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 the for the first time reported Cr-containing high entropy La1-xSrx(Co,Cr,Fe,Mn,Ni)O3-delta (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-delta material is documented to possess attractive properties as a candidate air electrode material for Solid Oxide Fuel Cells (SOFCs). Nanosized powders of the considered oxides are obtained using a 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 rhombohedral structural distortion (R3c symmetry) in the materials. High-temperature structural studies for the selected La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3-delta indicate the occurrence of a phase transition to an aristotype Pm3m structure at ca. 800 degrees C. The linear thermal expansion coefficient in the RT-1000 degrees C range is found to be moderate, 16.0(3) x 10(-6) K-1. The 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 degrees C. The maximum recorded conductivity for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3-delta composition exceeds 16 S cm(-1) in the 900-1000 degrees C range, being suitable for application. Furthermore, chemical stability toward the La0.8Sr0.2Ga0.8Mg0.2O3-delta (LSGM) electrolyte is proven. Considering the presence of chromium, typically deleterious to the performance, the measured value of the total cathodic polarization resistance for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3-delta-based electrode, being 0.126 omega cm(-2) at 900 degrees C, seems to be very attractive. The results obtained for a button-type fuel cell indicate power densities at a level of 550 mW cm(-2) at 900 degrees C. Therefore, it can be considered that the high entropy-based approach enables to propose alternative SOFC air electrode materials, with otherwise inaccessible chemical compositions.