Microstructure and oxidation behavior of composite Co–W/NiO coating on ferritic stainless steel for SOFC interconnector

In order to simultaneously improve the oxidation resistance and the electrical conductivity of solid oxide fuel cell (SOFC) interconnectors, a composite coating of Co–W/NiO was fabricated on ferritic stainless steel by composite deposition and pre-oxidation. Based on phase identification and microstructural analysis, the novel coating was confirmed to effectively suppress Cr diffusion to form a compact Cr-rich layer. Thus, the oxidation rate has been reduced to 9.46 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹, which showed a imporvement of 56.4% in oxidation resistance. The area specific resistance value of Co–W/NiO coated steel was evaluated as 27.6 mΩ cm², much lower than that of Co–W coating as 53.38 mΩ cm², which is adequate for SOFC application. Furthermore, the mechanism of the improvement has been investigated that the addition of NiO led to the formation of Ni–Co spinels and Ni–W composites, which affected the surface microstructure of the coating. Thus, the composite Co–W/NiO coated ferritic stainless steel exhibited the optimal combination for oxidation resistance and electrical conductivity.