Characterization of the Contact Resistance of Cathodic SOFC Contacting

DC conductivity experiments were carried out in order to characterize the area specific resistances (ASR) of various multi-layer-structures that represent the contacting interface between cathode and interconnect of state-of-the-art planar anode-supported SOFCs. The investigation focused on quantifying the influence of various chromium evaporation protection layer materials (MnO_x, MnCo_1.9Fe_0.1O₄ (MCF)), perovskitic cathode contact layers (LCC10, LCC12, LSCF), operational parameters during stack joining and the effect of pre-annealing of multi-layer samples on the overall ASR of the model system. The results demonstrated the influence of different material combinations as well as the duration of heat treatment during the joining process on the cell resistance, whereas we did not observe an obvious effect from pre-annealing. During the microstructural post-test analysis we found a coarsened and inhomogeneous microstructure of the MnO_x barrier layer, which indicates a strong interaction with the adjacent materials. In addition, the adhesion of those MnO_x layers deposited by wet powder spraying is lower when compared to MCF layers deposited by atmospheric plasma spraying, which contributed to long term behavior of the resistances obtained. With these results it is possible to give a recommendation for the choice of contacting and chromium evaporation layer system and the operational parameters during the first heat up of an SOFC stack.