Lifetime model for FSS interconnects based on chromium content

Abstract

The world is currently experiencing an unprecedented demand for energy. The high demand for energy is a result of the growth of human civilization and our consumption behavior. Electricity that is made from sources that are both green and renewable usually have a significant obstacle. The obstacle is that the energy production doesn’t always match the times for when energy is needed and therefore is reliant on energy storage. Solid oxide fuel cells (SOFC) are a potential solution to the problem as they can be used for power generation, long term energy storage, and reversible operations for grid support. Cost and lifetime are however currently two of the things holding SOFC back. A vital part of a SOFC is its interconnects, which are what electrically connect the individual cells of a fuel cell stack. Interconnects are also one of the main contributors to the cost of a SOFC and its lifetime. Today ferritic stainless steels (FSS) alloys are used for interconnects. FSS interconnects are cost-effective compared to preciously used ceramics, but degrade under the harsh operation temperatures in a SOFC. Coating the FSS have proven to be effective in reducing the corrosion phenomena that causes the degradation, such as the formation of chromium vapor and oxide scale growth. The thesis acts as a continuation of research that has been done to make SOFCs more commercially viable. More specifically it focuses on the concerns surrounding the lifetime of the interconnects. The research showed similar net mass gain for different FSS alloys in the same environment when they have been coated with a Ce/Co coating. Therefore different Ce/Co coatings have been examined. The aspects that have been investigated regarding the coating are primarily: (i) How does the coating effect lifetime of different FSS alloys; (ii) can the lifetime of coated FSS alloys be predicted; and (iii) how does cerium lead to improved lifetime. By investigating the corrosion behavior a lifetime model was constructed and a better understanding of how cerium contributes to protecting the alloys was gained.