Parameter Estimation for a Reconstructed SOFC Mixed-Conducting LSCF-Cathode
The performance of a solid oxide fuel cell (SOFC) is strongly affected by electrode polarization losses, which are related to the composition and the microstructure of the porous materials. A model that can decouple the effects associated with the geometr
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Abstract The performance of a solid oxide fuel cell (SOFC) is strongly affected by electrode polarization losses, which are related to the composition and the microstructure of the porous materials. A model that can decouple the effects associated with the geometrical arrangement, shape, and size of the particles together with material distribution on one side and the material properties on the other can give a relevant improvement in the understanding of the underlying processes. A porous mixed ionic-electronic conducting (MIEC) cathode was reconstructed by focused ion beam tomography. The detailed geometry of the microstructure is used for 3D calculations of the electrochemical processes in the electrode and to calibrate a well-established reduced model obtained by averaging. We perform a modelbased estimation of the parameters describing the main processes and estimate their confidence regions using the calibrated reduced model. Keywords SOFC • Sensitivity • Parameter Estimation • 3D FEM model • 3D Reconstruction
1 Introduction The electrochemical performance of solid oxide fuel cells (SOFCs) mostly depends on material composition and microstructure of the porous electrodes, which are the determinant causes of polarization losses. In this work a three-dimensional T. Carraro () Institut f¨ur Angewandte Mathematik (IAM), Ruprecht-Karls-Universit¨at Heidelberg, 62120 Heidelberg, Germany e-mail: [email protected] J. Joos Institut f¨ur Werkstoffe der Elektrotechnik (IWE), Karlsruher Institut f¨ur Technologie (KIT), Adenauerring 20b, 76131 Karlsruhe, Germany e-mail: [email protected] H.G. Bock et al. (eds.), Model Based Parameter Estimation, Contributions in Mathematical and Computational Sciences 4, DOI 10.1007/978-3-642-30367-8 13, © Springer-Verlag Berlin Heidelberg 2013
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reconstruction of a mixed conducting La0:58 Sr0:4 Co0:2 Fe0:8 O3ı (LSCF)-cathode, that provides a detailed microstructure approximation, is considered. Mixed conductors have both electronic and ionic conducting properties, thus allowing the active zone of the electrodes to extend from the three phase boundary towards the inner volume of the electrode. The mechanisms that allow such an extension are related to oxygen ion diffusion within the MIEC and oxygen surface exchange at the interface between MIEC and gas phase. In this work the exchange of oxygen with the gas phase is described by the surface exchange coefficient k ı and the transport of oxygen ions by the chemical diffusion coefficient D ı as shown in [4, 18, 19]. In the last few years several groups have developed different methods for the reconstruction of a porous electrode [7, 9, 11, 22, 26, 27] in order to study the influence of the microstructure on the performance of the electrode. Two tomography techniques are considered for the reconstruction of SOFC electrodes: X-ray and focused ion beam (FIB). The latter is considered to be most suitable in our case (particle size between 300 and 600 nm), as it allows a finer resolution.
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