Chromium Oxidation and Evaporation on Interconnects from a Stack and CHP-Systems Perspective

Regardless of the material used for interconnects in SOFC stacks, whether it is based on ferritic stainless steels or on chromium based material systems, chromium oxide scales will be formed on the interconnects' surface during operation. In connection to the oxide scale formation, chromium evaporation is a commonly observed and researched issue. It was shown that evaporated chromium species did not harm the cathode's performance significantly for more than 40.000 h of continuous operation in both short stack and full stack level with the Hexis repeat unit concept. Short stacks with varying operation times were subjected to post-mortem analysis and characterized for oxide scale thicknesses. Additionally, an effective chromium filter system based on a perovskite material system was designed and integrated into the exhaust gas stream before the heat exchanger. The filter concept was operated for more than 10.000 h in Hexis CHP-systems, some on full and, some on part load. During the experiments, condensate samples were taken in regular intervals and none of them contained Cr species.