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TECHNICAL PAPERS

Characterization of Fuel Cells and Fuel Cell Systems Using Three-Dimensional X-Ray Tomography

[+] Author and Article Information
Stefan Griesser

Department of Eco:Energy Engineering, Upper Austrian University of Applied Sciences, Stelzhamerstrasse 23, A-4600 Wels, Austrias.griesser@fh-wels.at

G. Buchinger, T. Raab, Dieter Meissner

Department of Eco:Energy Engineering, Upper Austrian University of Applied Sciences, Stelzhamerstrasse 23, A-4600 Wels, Austria

D. P. Claassen

 alpps fuel cell systems, Exerzierplatzstrasse 4, A-8051 Graz, Austria

J. Fuel Cell Sci. Technol 4(1), 84-87 (Mar 31, 2006) (4 pages) doi:10.1115/1.2393309 History: Received December 01, 2005; Revised March 31, 2006

Three dimensional (3D) computer aided X-ray tomography (CT) has proven to be an extremely useful tool in developing our own as well as in examining commercially available solid oxide fuel cells. The results of 3D-CT measurements became very important for understanding the functionality of our first generation and improving the development of our second fuel cell generation. Also geometrical measurements, especially the roundness and the straightness of the tube, can be evaluated, both critical parameters when the stack is heated and mechanical stress has to be avoided. By using this technique the structure of the first generation cells proved to be of insufficient quality. Problems like the variation in thickness of the electrolyte tube as well as the homogeneity in thickness of the electrodes deposited can easily be detected by this nondestructive technique. Microscopic investigations of this problem of course provide equal results, but only after cutting the samples in many slices and many single measurements of different areas of the fuel cell. Using cells with inhomogeneous thickness of course results in drastic variations of the current densities along a single cell. Electrolyte layers that are too thick will result in power loss due to the increased resistance in the ionic conductivity of the electrolyte. If the electrolyte of an electrolyte supported cell is too thin, this can cause mechanical instability. Problems can also occur with the leak tightness of the fuel cell tube. Gas diffusion through the electrode layer can become a problem when the thickness of the electrode layer is too high. On the other hand, if the layers are too thin, the result can be a discontinuous layer, leading to a high electrical series resistance of the electrode. Besides determining the thickness variations also the porosity of the electrolyte needs careful attention. Larger cavities or shrink holes form insulating islands for the ion-stream and are therefore limiting the ionic conductivity. They are also diminishing the mechanical stability and provide problems for depositing a closed electrode film in electrode supported cells.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Axial slice of a SOFC tube: pores of different sizes limit the ionic conductivity. Figure inside: Cutout from a slice on another position: Hole in the electrolyte creating stability problems.

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Figure 2

Front view of a bad electrolyte cross section. Measurements of the ion conductivity underline the result. The outer cylinder fit shows an aberration in straightness on the lower left side.

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Figure 3

Axial slice for determining the roundness of a pure electrolyte. A cylinder fit was made on the inside surface of the whole 3D dataset.

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Figure 4

Frontal slice of a microtubular SOFC with two measurement points on the anode layer

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Figure 5

Axial slice with electrical conductance type “cage;” only near the doted circled part is a contact with the surface

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Figure 6

Frontal slice through the newly developed current ducts. About six contact points/mm2 can be found.

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Figure 7

Cross section through the stack—a blocked tube was detected

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Figure 8

3D view of a fuel cell stack calculated from the X-ray data

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Figure 9

Frontal slice (high resolution micro-CT) of a fuel cell fixed by a special sealing technique. The bad quality at the crossing point is due to scattering radiation.

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Figure 10

Interconnection of the cell with the membrane (cutout of a low resolution CT image). Left: Frontal slice of a good connection and of a gas leak. Right: Axial slice of the gas leak from left.

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