Copper-Magnesium-Manganese Spinel Coatings for Solid Oxide Fuel Cell Interconnects

The properties of Cu-Mn-O spinels containing Mg were studied for use as protective coatings on UNS430 stainless steel interconnects in solid oxide fuel cells. Cu-Mn-Mg-O spinel coatings were formed by oxidizing electrodeposited copper, manganese, and magnesium hydroxide films in air at 800°C. A base layer of copper aided uniform manganese deposition and uniform spinel formation. The Mg-Mn-O pseudobinary phase diagram based on XRD results shows a wide range of spinel non-stoichiometry. The CuMn2O4 spinel coating has higher conductivity (∼100 S/cm at 800°C) but exhibited buckling defects. Addition of magnesium to the Cu-Mn-O spinel coatings significantly reduced the buckling damage. Although the measured electrical conductivity of MgMn2O4 is 1–2 S/cm at 800°C, Cu0.7Mg0.3Mn2O4 has a conductivity of ∼60 S/cm at 800°C. Cu-Mn-Mg-O spinel coatings also protect stainless steel by significantly reducing chromium oxide scale formation and diffusion of chromium into the coatings with the advantage of relatively high conductivity.