Composition-gradient protective coatings for solid oxide fuel cell interconnectors

•Protective Ni-based coatings on stainless-steel current collectors were developed.•Testing under solid oxide fuel cell (SOFC) cathodic conditions for 21,000 h.•Ni-based coatings effectively suppress Cr diffusion from the steel at 1123 K.•Microstructure and composition gradient in the reaction layers were studied. Protective Ni-based coatings for stainless steel current collectors of the planar solid oxide fuel cells (SOFCs) were developed and tested during 21,000 h in contact with lanthanum-strontium manganite cathode material. The compositional and microstructural alterations due to interdiffusion between Ni coating, La0.8Sr0.2MnO3 electrode and commercial Crofer 22 APU steel after long-term testing under the SOFC cathodic conditions, were studied. The results of micro-Raman spectroscopy and electron microscopy analyses showed a dominant role of Mn and Fe diffusion into the protective coating, leading to the formation of NiFe2O4 and MnFe2O4. Although Mn deficiency in the manganite cathode may decrease electrical conductivity, its impact on the overall contact resistance is insignificant. The Ni-based coatings were found to decrease area-specific interfacial resistivity down to 3–4 mOhm × cm2 for, at least, 21,000 h (>2.5 years) at 1123 K, atmospheric oxygen pressure and current density of 0.5 A/cm2.