Stack-like Contacting in Solid Oxide Cells: Electrochemical Characterization and Modeling

The integrity of metallic interconnectors (MIC) in an SOC-stack is crucial since contact resistances or limitations in gas supply may occur. In this contribution, a Crofer 22 APU$^®$ interconnector with a $\textrm{(Mn, Co, Fe)}_{3}\textrm{O}_{4}$ spinel oxide (MCO) coating and a lanthanum-strontium-manganese-cobalt oxide (LSMC) contact layer at the air side was investigated. The electrochemical behavior was characterized by means of IV-characteristics, impedance spectroscopy and DRT analysis. In particular, the contact losses at the air side were measured with targeted potential probes. With respect to the contact layer mounted in a dried state, the application of a stack-like clamping pressure of 1 MPa showed a significant decrease of the contact resistance. In order to extend an existing zero-dimensional performance model for an electrolyte-supported cell with a Ni/GDC fuel electrode and LSCF air electrode, a method was established to parameterize contact losses at the air electrode. The observed activation energy of the contact losses showed to be independent of the clamping pressure. Additionally, the dependency of the cell´s intrinsic ohmic losses towards the steam partial pressure at the Ni/GDC fuel electrode was quantified and included to the model. Simulation studies were validated with experimental data for technical operating conditions.