Effect of Cathode Contacting on Anode Supported Cell Performances and Degradation

Stacking Solid Oxide Fuel Cells implies the use of contacting layers, especially in the cathode compartments where ohmic losses are introduced at the interface between the electrode and the interconnect  due to the high interfacial resistance and the lowered contact area caused by geometrical and porosity issues. Such losses compromise the current distribution over the electrodes strongly influencing the system performances in terms of power outputs. The contacting issues are weakly dependent on the operating conditions compared to other dissipative contributions related to the cells. This implies the need to solve them at the structural level in order to ensure high system performances. A dedicated testing setup has been used to test anode-supported cells with different contacting solutions. The contact geometry effect has been evaluated comparing the use of platinum meshes and stamped metallic bipolar plates (Crofer 22 APU) as current collectors. Additionally, the application of a La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) paste between the cathode and the interconnect allowed to estimate the beneficial effect of the contacting layer enhancing the current distribution at the cathode side of the cell. The system performances have been investigated by means of current-voltage curves. Electrochemical impedance spectroscopy measurements were carried out to distinguish the loss contributions within the system and study the degradation phenomena. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction techniques were adopted as post-experiment characterization to investigate microstructural changes and elements migration in order to confirm the observed changes in performances.