Structure and electrical properties of Cu-doped Mn-Co-O spinel prepared via soft chemistry and its application in intermediate-temperature solid oxide fuel cell interconnects

The study describes CuxMn1.25-0.5xCo1.75-0.5xO4 (x = 0, 0.1, 0.3 and 0.5) spinels synthesized using EDTA gel processes in order to optimize the performance of high-quality spinel protective-conducting films deposited on steel interconnects. The powders obtained after 12 h of calcination in air at 1073 K are solely cubic spinels. Sintering these spinels for 12 h in air at 1423 K also leads to the formation of small amounts of CoO, Mn2O3 or CuO; the type of phase depends on the quantity of copper introduced into the manganese-cobalt lattice. The highest electrical conductivity at 1073 K is observed for Cu0.3Mn1.1Co1.6O4 (162 S·cm−1), which is closely correlated with the lowest activation energy of conduction over the entire temperature range (373≤T≤1073 K); the lowest conductivity is measured for Mn1.25Co1.75O4 (84 S⋅cm−1). The study confirms the suitability of the Cu0.3Mn1.1Co1.6O4 spinel as a potential material for the preparation of protective-conducting coatings on the surface of the DIN 50049 ferritic steel applied in IT-SOFC interconnects. The area-specific resistance of coated steel is 0.08 Ω·cm2, which is lower than that of bare steel after 300 h of oxidation at 1073 K. Cr vaporization tests show that the Cu0.3Mn1.1Co1.6O4 coating is efficient at blocking the outward diffusion of chromium.