Pre-Coated Ce/Co-Coated Steel: Mitigating Cr Vaporization, Increasing Corrosion Resistance at Competitive Cost

Abstract

Cr vaporization and oxide scale growth are probably the two most detrimental degradation mechanisms associated to Cr2O3-forming alloys as interconnect material in SOFC. Different type of perovskite or spinel coatings are commonly used to mitigate Cr vaporization. Furthermore a number of studies have suggested that reactive element coatings (Ce, La, Hf) can reduce the oxidation rate of Cr2O3-forming alloys. However, the use of coatings increases cost due to addition processing and handling costs. The present study investigates the effectiveness of thin Ce and Co Physical Vapor Deposited (PVD) coatings with respect to Cr vaporization, corrosion resistance and Area Specific Resistance (ASR). The coatings were applied in a continuous roll-to-roll process which allows for high volumes. The use of pre-coated interconnects is thus more economic than a batch process. However, a consequence of the pre-coated concept is that the coating is subject to deformation when the pre-coated steel is pressed into the interconnect shape. Therefore this study also investigates the effect of deformation on the coating. Coated steel strips were bi- and uniaxially deformed. Furthermore a commercially used interconnect shape is investigated and the effects on Cr evaporation and corrosion are studied: Cr vaporization was measured in an air-3% H2O environment at 850 °C for 336 h. The results revealed that when the pre-coated steel was deformed, large cracks were formed. However, upon exposure those cracks did heal forming a continuous surface oxide rich in Co and Mn. As an effect of the rapid healing, no increase in Cr vaporization was measured for the pre-coated material.