Jochen Joos

Dr.-Ing. Jochen Joos

  • Institut für Angewandte Materialien - Werkstoffe der Elektrotechnik (IAM-WET)
    Adenauerring 20b
    Gebäude 50.40
    D-76131 Karlsruhe

Solid Oxide Fuel Cell: Modeling and Simulation

Fig. 1: Transport and reaction mechanisms in a SOFC

Fuel cells (FC) convert chemical energy directly into electricity. FCs avoid the detour of conven­tional power generating systems over thermal and mechanical energy and the limitation by the Carnot cycle. The lead in efficiency makes FCs a future technology for resource-saving and economic generation of electrical energy.
Among different types of FCs the ceramic high temperature solid oxide fuel cell (SOFC) is consid­ered the most flexible one. Appli­cations of the SOFC compete with old fashioned but well estab­lished technologies. In order to substitute these in the long term, it is still necessary to further in­crease the so far reached per­formance of the SOFC. The per­formance of a SOFC is limited by electrode polarisation processes, depending both on material com­position and microstructure char­acteristics. One goal of this pro­ject is the detailed investigation of the interaction between micro­structure and polarisation resis­tance within the electrodes. The main stress is on the model-based design and optimization of the electrode microstructure.

Fig. 2: left: SEM picture of a porous cathode, right: 3D FEM-Model
At the IAM-WET a three-dimensional Finite Element Method (FEM) model for the electrode micro­structure has already been devel­oped and implemented in the FEM software package COMSOL Multiphysics. The model enables the prediction of the electrode performance in dependence of the reproduced microstructure and material parameters. The model allows only the simulation of microstructures consisting of equally sized particles.
A part of this project is the further development of this model. Espe­cially the real electrode micro­structure should be approximated in more detail in the model. One way to achieve detailed microstructures for simulation is by the use of a “cross beam” FIB/SEM-setup (Focused ion beam combined with scanning electron microscope).

Fig. 3: 3D-Rekonstruction of a cathode with the use of a FIB/SEM-setup
FIB/SEM-techniques combined with image processing has the potential to reconstruct 3D data of actual electrodes.
Presently no commercial software has the ability to use such 3D reconstructions directly as ge­ometry for simulations, or at least is able to approximate the actual microstructure with enough accu­racy. Therefore, in cooperation with the Institute of Applied Mathematics from the University of Heidelberg, a software called “ParCell3D” is under develop­ment, using high performance computing techniques. ParCell3D is based on the 3D FEM-Model implemented in COMSOL Multi­physics and has the ability to solve complex structures parallel on a high performance computer. Simulations with ParCell3D are carried out on the national high performance computer of Baden Württemberg, a HP XC6000.
The simulation of detailed micro­structures enables a qualitative and quantitative investigation of the interaction between micro­structure and electrode perfor­mance. The obtained expertise can be use to optimize the microstructure of the electrodes. Hence the performance of fuel cells can be increased.

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Publications and Conference Proceedings

Please refer to the German website for a list of publications and presentations at conferences.