Pulse Electrodeposition of Cobalt/Zirconia Coatings: Oxidation and Electrical Performance of Ferritic Stainless Steel Interconnects

To enhance oxidation resistance, avoid Cr evaporation and preserve suitable electrical behavior of Crofer 22 APU stainless steel as the interconnect of solid oxide fuel cells, Co/ZrO2 composite coatings were applied on Crofer 22 APU using the pulse electroplating technique. Moreover, isothermal and cyclic oxidation measurements were used to investigate oxidation resistance. In addition, oxidation rates were estimated and microstructures of the coatings were investigated before and after the oxidation tests. According to the results, the coated specimen had a lower oxidation rate constant than the uncoated specimen after 500 h of oxidation. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction analysis showed that the oxide scale formed on the coated steel after oxidation was composed of two layers. The results also showed that the inner layer is thinner and contains Cr and O, while the outer layer is composed of Co, Mn, Cr and O. Furthermore, ZrO2 particles were also found in the outer oxide layer, following the oxidation tests. The Co/ZrO2-coated steel has a thinner inner oxide layer and a lower oxidation rate than the uncoated steel. Additionally, the area-specific resistance (ASR) of the steels with and without coating was also estimated as a function of temperature and time. The results showed that the growth rate of Cr2O3 layer decreased after applying the Co/ZrO2 composite coating, which resulted in lower ASR value. Moreover, after 500 h of oxidation at 800 degrees C, the ASR value of the Co/ZrO2-coated and uncoated steels was 13 m omega cm(2) and 27.8 m omega cm(2), respectively.