Performance limiting factors in anode-supported cells originating from metallic interconnector design

Abstract

The combination of advanced characterization techniques and FEM-simulations provided detailed information about losses related to the flowfield geometry of a metallic interconnector (MIC) in a planar SOFC repeat unit. The presented 2-D FEM model is able to predict the repeat unit performance decrease due to the in plane ohmic losses in the electrodes and the contact resistance between electrode and MIC. The performed calculation and measurement showed an increase of ohmic losses of up to 84% when the single cell was contacted with a MIC, The contact resistance adds less than 6% on the cathode side. The in-plane current flow from the contact ribs to the triple phase boundaries under the gas channels caused 94% of the additional ohmic losses. Analysis of impedance spectra by the distribution of relaxation times and a subsequent Complex Nonlinear Least Squares fit separated gas diffusion from the total polarization losses. Depending on flowfield design, the gas diffusion resistance on the cathode side increased up to +750%. For high-performance anode supported cells, the choice of cathode flowfield design added up to 41% power loss, whereas the anodic flowfield design was of minor importance (<1% power loss).