Development of Mn-Co and Mn-Co-CeO2 Coatings on Crofer 22 APU Steel for Solid Oxide Fuel Cell Interconnects

Abstract

The present study compared the performance of uncoated, Mn-Co and Mn-Co-CeO2-coated Crofer 22 APU ferritic stainless steel interconnects. The samples were oxidized for 500 h in an electric furnace at 800 °C. The surface morphology and phase structure of the samples before and after oxidation were examined using FESEM microscopy and X-ray diffraction (XRD) analysis, respectively. The electrical conductivity evaluation of the samples was also conducted by measuring the area specific resistance (ASR). The results indicated that the weight gain of the uncoated, Mn-Co and Mn-Co-CeO2-coated samples after 500 h of oxidation was 0.55, 0.58 and 0.27 mg.cm−2, respectively. Additionally, a comparison of the oxidation kinetics of the experimental samples revealed that the oxidation rate constant of the Mn-Co-CeO2-coated steel is 10 and 40 times lower than that of the Mn-Co-coated and uncoated steel, respectively. XRD analysis of the samples after oxidation confirmed the presence of MnCo2O4, Co3O4, and (Mn,Cr,Co)3O4 in the oxidized Mn-Co-coated, MnCo2O4, Co3O4, and CeO2 in the oxidized Mn-Co-CeO2-coated, and the chromium-containing phases (FeCr2O4, MnCr2O4, and Cr2O3) in the oxidized uncoated samples. The presence of phases with high electrical conductivity in the oxidized coated samples reduced their activation energy for conduction compared to the oxidized uncoated sample.