Development of cathode contacting for SOFC stacks

In SOFC stacks the electrical contact between the ceramic cathode layer and the metallic interconnector (IC) has to be adjusted carefully to minimize the contact resistance and slow down degradation mechanisms. In JÜLICH, ICs made of Crofer22APU are coated with a MnCo1.9Fe0.1O4 spinel (MCF), applied by atmospheric plasma spraying (APS), which successfully prevents the diffusion of volatile Cr species from the steel into the cell. Materials for the cathode contact layer have to be sufficiently good electronic conductors, stable in oxidizing atmosphere, chemically stable and compatible with the adjacent layers, and show a thermal expansion behavior similar to MCF and the cathode material, i. e. La0.58Sr0.4Co0.2Fe0.8O3-x (LSCF).To obtain an optimal contact layer, different aspects such as material properties, microstructure, and processing have to be considered. Here we compare various materials regarding their electrical conductivity and compatibility with each other and discuss different processing routes for the application of the cathode contact layer. DC conductivity measurements and scanning electron microscopy (SEM) imaging give information on the correlation of material properties and microstructure. We conclude that an LSCF contact layer with coarse porosity on top of the fine structured LSCF cathode is the most suitable contacting for JÜLICH SOFC stacks