Performance of MIEC Cathodes in SOFC Stacks Evaluated by Means of FEM Modeling

Solid oxide fuel cells (SOFC) are connected in series to stacks by metal interconnectors (MIC). Hereby, the potentially high performance of anode-supported cells (ASC) is significantly reduced. [1,2]. Conclusively, gas diffusion polarisation at the mixed conducting cathode contributes close to the sum of all ohmic losses to the overall polarization, both controlling stack performance.

In order to investigate the matter further, a 2D FEM repeat unit model was developed, which accounts to ohmic and polarisation loss on a stack level [3]. In the model the physical processes i) gas diffusion in the porous electrodes, ii) electric /ionic conduction in the electrodes and electrolyte as well as iii) the electrochemical electrode reactions are incorporated. Electrode microstructure is implemented via 3D reconstruction of FIB-tomography images [5,6]. Electrode kinetic parameters are determined via EIS evaluations [4]. Performance predicted by the model was validated with the help of current/voltage-characteristics measured on high performance anode supported cells.

The model calculations demonstrate the interdependence of cathode material parameters (thickness, porosity, conductivity, electrode kinetics) and MIC-design, and widen the understanding on their influence on stack performance. The results show i) that an optimal MIC-design depends on the cathode material parameters and ii) a well-chosen cathode thickness increases the overall power output.

[1] L. Blum, W. A. Meulenberg, H. Nabielek, R. Steinberger-Wilckens, Worldwide SOFC Technology Overview and Benchmark, International Journal of Applied Ceramic Technology2 pp. 482-492 (2005).
[2] M. Kornely, A. Leonide, A. Weber, E. Ivers-Tiffée, Journal of Power Sources 196 (17), pp. 7209-7216 (2011).
[3] H. Geisler, M. Kornely, A. Weber, E. Ivers-Tiffée, ECS Trans. 57, pp. 2871-2881 (2013).
[4] A. Leonide, Y. Apel, E. Ivers-Tiffée, ECS Trans. 19, pp. 81-109 (2009)
[5] J. Joos, T. Carraro, A. Weber, E. Ivers-Tiffée, J. Power Sources 196, pp. 7302-7307 (2011).
[6] J. Joos, M. Ender, I. Rotscholl, N. H. Menzler, E. Ivers-Tiffée, J. Power Sources 246, pp. 819-830 (2014)