Preparation of Nanocrystalline Spinel as Interface Layer on Steel Interconnects for Solid Oxide Fuel Cells (SOFCs) Applications

Abstract

In recent years, due to reduction of operating temperatures (e.g., 500-800 oC), IT-SOFCs have been drawn a lot of attention. At lower working temperatures, metallic materials as interconnects replaced conventional LaCrO3-based ceramics. Feritic stainless steel alloys such as Crofer 22 and AISI 430 are vastly utilized for metallic interconnects, because of their relatively high conductivity and appropriate thermal expansion behaviors. However, exposure of those alloys to an oxidizing atmosphere during operating hours leads to Cr2O3 scales formation as interface layer between interconnect and cathode (Cr poisoning phenomenon). The continuous growth of the oxide scale allows other Cr-containing species deposition that prevent normal flow of electrons diffusion between different electrodes and block the active sites on cathode side so retard the oxygen reduction process allow lower conductive species layer formation. The most reliable solution to these problems is applying a protective layer with specific criteria on the surface of metallic interconnect. The acquired criteria for protective layer assure appropriate thermal and mechanical stability, high density, excellent electrical conductivity and tune with interconnect substrate. The most common types of the coated materials are rare earth perovskites, spinels, and MAlCrYO (M stands for a metal). Divalent spinel oxides composed of Mn, Co, Ni,Cu, and Fe have been attracted significant attention. In particular, the most studies focused on spinel structure of (Mn,Co)3O4 as a promising composition where it showed a good effect on prevention Cr2O3 scale growth at long-term evaluations. Several studies pay a lot of efforts to improve the coating layer properties by modification with different transition elements such as Cu, Ni and Fe. Mn-Co oxides coatings can also be synthesized by simple and cost-effective processes, such as screen printing, slurry coating, and electrodeposition. In this context, optimizing the synthesis conditions of the spinel structure by screen printing for pure and modified Mn-Co oxides was focused. Besides, close investigation of all synthesized phases with deep study of the modified elements effects on various phase properties. Moreover, designing heat treated coating with high quality matching very well with the utilized alloy.