The structural, thermal and electrochemical properties of MnFe1−x-yCuxNiyCoO4 spinel protective layers in interconnects of solid oxide fuel cells (SOFCs)

Cu and Ni substitutions are investigated at spinel MFCO (Manganese Iron Cobalt Oxide) components using a variety of characterization techniques, including XRD, XPS, RAMAN spectroscopy, SEM, TGA, dilatometer measurements, and electrochemical investigations. MnCu0.25Fe0.25Ni0.5CoO4 and MnCu0.5Fe0.25Ni0.25CoO4 spinel oxides were prepared and evaluated as a copper-nickel MFCO protective coating layer on the commercially available 316 L stainless steel interconnect for intermediate temperature solid oxide fuel cells (IT-SOFCs). XRD analysis indicates that both powder samples contain a single phase with a cubic structure. In both compounds, mixed Mn3+/Mn4+, Co2+/Co3+, and Cu+/Cu2+ couples are found, showing that co-doping of Ni and Cu into the MFCO spinel resulted in the redistribution of Mn and Co ions (Mn3+, Mn4+, Co2+, and Co3+) into the octahedral sites, which contributed to the increase in electrical conductivity. MnCu0.5Fe0.25Ni0.25CoO4 exhibited a maximum conductivity of 54 S cm−1 at 750 °C. Following the area-specific resistance (ASR) of the scale/coating during heating and cooling cycles was used to evaluate the protective action of the coating applied to 316 L stainless steel. Postmortem microstructural analysis of the screen-printed coatings showed good protection against chromium diffusion. [Display omitted] •New MnFe1−x-yCuxNiyCoO4 spinel protective layers fabricated by sol-gel auto-combustion and screen printing technology.•The crystal structures and morphologies of the bulk and film materials were deeply investigated.•Thermogravimetric and thermal expansion analysis confirmed the higher stability of Ni-rich spinel compounds.•The electrical performances for the coated films on metallic interconnects were evaluated by ASR and DC measurements.