SOFC Modeling - From Micro-Kinetics to Stacks

This paper presents a hierarchical modeling approach for Solid-Oxide Fuel Cells from elementary kinetics to stacks. On a fundamental level, we have developed an analytical model for the evaluation of volume specific three-phase boundary length (vLtpb) in composite electrodes and electrochemical kinetics expressions to account for coverage dependent activation energies of various surface adsorbed species. The kinetics are applied for modeling SOFCs operating on various reformate compositions. The results of both fundamental modeling approaches are compared with experimental data [1, 2]. On an application level, a novel approach for modeling a SOFC stack is presented. The approach is based on decoupling heat transfer from the other processes [3] and a newly developed cluster agglomeration algorithm, which drastically reduces the computational costs associated with stack simulation. Based on the assumption that all unit cells with similar temperature profiles behave alike, the cells are divided into clusters according to differences in their local temperature profiles. All unit cells of one cluster are then represented by one cell, for which a simulation is conducted, which applies detailed models for electro-chemical conversion at the three-phase boundary, an elementary-step reaction mechanism for the thermo-catalytic conversion of the fuel on the catalyst in the anode [4], dusty-gas model to account for multi-component diffusion and convection in the electrodes, and a plug-flow model for the flow in the fuel and air channels.