An Analysis of Contact Problems in Solid Oxide Fuel Cell Stacks Arising from Differences in Thermal Expansion Coefficients

The successful operation of solid oxide fuel cells (SOFC) imposes high demands on the similarity of the thermal expansion coefficients of the materials used. This is not only due to thermo-mechanical factors but also because of the risk of contact loss via the formation of a micro-gap between the electrodes and adjacent contact layers caused by temperature changes. The origin of the formation of such a gap between the different layers in an SOFC stack is investigated on the basis of various material combinations. A comparison with successful and failed stack test results reveals that there is a high probability of contact problems if the calculated gap on the cathode side exceeds 200 nm. This limit relates to the maximum possible elastic deformation of the combination of the cathode and cathode contact layer (CCL). Such contact problems can be avoided in the current design by utilizing an appropriate combination of the cathode, CCL and glass-ceramic material that can be selected on the basis of the methodology outlined in the current work. This optimization in materials selection will help to establish a stack technology that allows high power density with a minimized risk of failure of single layers.