Stationary FEM Model for Performance Evaluation of Planar Solid Oxide Fuel Cells Connected by Metal Interconnectors

A modeling framework is presented based on a stationary finite element method (FEM) model. The model geometry is a two-dimensional repeat unit representing all individual layers of an anode supported cell sandwiched between metallic interconnect (MIC) structures. The model is capable of analyzing performance limiting factors for planar solid oxide fuel cell (SOFC) stacks. These factors arise from material composition, microstructure, layer thickness, or MIC flowfield design. Herein, setup and validation of the modeling framework are presented and discussed in detail. Charge-transfer chemistry is modeled with detailed Butler-Volmer kinetics. Ion and electron conduction is modeled with Ohm's law and porous-media gas species transport is represented by the Dusty-Gas model. All physical parameters in the model equations were determined by our own measurements, conducted on anode supported cells and components thereof. The stationary finite element model was validated against measured current/voltage characteristics for a temperature range of 621 to 871°C, fuel humidification from 5.5% to 60%, and current densities up to a maximum of 2 A/cm2. This more than exceeds the standard operating range for multi-kW SOFC stack units. The applicability of the model is demonstrated using the electrical and dimensional data of anode supported cells and the MIC design similar to stationary 5 and 10 kW stacks (from Forschungszentrum Jülich). It is shown that the MIC flow field design induces gas transport limitations and electronic current constrictions in the cell components. The simulation results clearly indicate the cathode layer thickness as the most sensitive factor in limiting stack performance.