Improved interconnect materials for next-generation Solid Oxide Fuel Cells

Abstract: Solid Oxide Fuel Cells (SOFC) are attractive candidates in the search for cleaner and energy efficient production due to their numerous advantages such as fuel flexibility, modularity and exceptional efficiencies when combined heat and power is harnessed. A key element in its design are the interconnects which are mainly manufactured from custom ferritic stainless steels to carry the electricity between two adjacent cells. However, the high operation temperatures increase the chromia scale thickness in those steels, which reduces their conductivity. At the same time, chromium (VI) volatilization due to the wet atmosphere poisons the electrodes and reduces the cell life. Therefore, the narrow of the selection of suitable materials and high production costs have hindered their commercialization. Recent advances in lower temperature SOFC operation have opened a window for new interconnect materials and innovative processes. A Ce/Co nanocoating can be applied in the readily available AISI 441 ferritic steel to form a protective spinel oxide layer that reduces the effect of both degradations in the interconnects. The coating is applied in a continuous roll-to-roll process and then the interconnect shape is pressed in the material, manufactured as Sanergy HT 441 by Sandvik. However, mechanical stresses cause microcracks that expose the substrate material, which can impact the oxidation behaviour negatively. Fortunately, pre-treatments can achieve the spinel to diffuse over short distances and combine with elements in the substrate, homogenizing the protective effect. This phenomenon known as self-healing has not been studied with sufficient depth for the Sanergy HT 441. Thus, different series of temperature and short pre-treatments times were tested, and self-healing properties were observed by means of SEM surface characterization and chemical analysis. The results indicate that self-healing can be obtained within short times using isothermal pre-treatments at temperatures over 750 °C.