Investigation of the formation of La1-xSrxC1-yFeyO3-d cathode materials and their interaction with electrolyte substrates for potential it-sofc applications

Abstract

Cathode layers of IT-SOFC (Intermediate Temperature Solid Oxide Fuel Cell) materials are investigated to find out the reactions leading to the formation of La0.6Sr0.4Co0.8Fe0.2O3 and La0.6Sr0.4Co0.2Fe0.8O3 on the surface of either ZrO2 or CGO (Cerium-Gadolinium Oxide) electrolyte substrates. Precursor salt powders were blended, compressed and placed on discs of sintered ceramic electrolytes before being heated in a laboratory furnace at 800oC for 1h. Almost all combinations of LSCF salt mixtures were prepared and analyzed by SEM-EDS, XRD and DTA-TGA to see if all solid state reactions are completed and what new phases eventually formed in LSCF combinations. Most of the transformation was complete after 1050oC heat treatment to yield oxides. According to XRD analysis it was observed that La plays a significant role to enable the formation of new phases. In the absence of La, other salts had significant difficulty to react to form new phases. Also, Sr tends to swap its chloride with nitrate of other salts in salt mixtures after drying in oven. SEM-EDS analysis of the interface between the electrolyte and LSCF showed that there was weak mutual diffusion of the constituent elements between the cathode layer and the electrolyte. The cathode layer was usually in porous form but was found to spread well over the substrate. Uneven diffusion of La, Sr, Co or Fe into the substrate had little influence on the stoichiometry of the resulting coating layer. Unlike 6428 samples, it was possible to form stoichiometric LSCF in 6482 samples.