Oxidation behavior of Cu-doped MnCo2O4 spinel coating on ferritic stainless steels for solid oxide fuel cell interconnects

Spinel oxides with the general formula of MnCuxCo2−xO4 (x = 0.1, 0.3, 0.5, 0.7 respectively) are used as coating materials on the metallic interconnect SUS 430 alloy to reduce the cathodic performance degradation by Cr poisoning and the interfacial resistance to improve the surface stability. The effect of Cu doping at the B position of spinel on the electrical conductivity and coefficient of temperature expansion (CTE) is investigated to determine the oxidation behavior and effectiveness as a protective layer. The result confirms that MnCu0.5Co1.5O4 spinel shows highest electrical conductivity of 105.46 S cm−1 at 750 °C in air and an average CTE value of 12.27 × 10−6 K−1 at temperature range of 20-960 °C. MnCu0.5Co1.5O4 coating is stable enough after 2000 h cyclic oxidation at 750 °C. The growth of Cr2O3 and formation of MnCr2O4 in the scale layer are effectively suppressed by the presence of MnCu0.5Co1.5O4 coating. The oxidation kinetics obeys the parabolic law with a rate constant as low as 2.76 × 10−15 g2 cm−4·s−1 and the ASR contributed by the oxide scale is 8.04 mΩ cm2 at 750 °C. The research indicates that MnCu0.5Co1.5O4 is a promising coating material for metallic interconnects of the intermediate temperature solid oxide fuel cells.