Research Papers

Modeling and Study of the Influence of Sealing on a Solid Oxide Fuel Cell

[+] Author and Article Information
Zacharie Wuillemin

Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Industrial Energy Systems (LENI), CH-1015 Lausanne, Switzerlandzacharie.wuillemin@epfl.ch

N. Autissier, A. Nakajo, M. Luong, J. Van herle, D. Favrat

Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Industrial Energy Systems (LENI), CH-1015 Lausanne, Switzerland

J. Fuel Cell Sci. Technol 5(1), 011016 (Feb 07, 2008) (9 pages) doi:10.1115/1.2784333 History: Received November 30, 2005; Revised December 13, 2006; Published February 07, 2008

The properties of sealing materials are important for the performance and reliability of solid oxide fuel cells (SOFCs). Even if the properties of a sealing material can be studied separately, it remains difficult to quantify the effect of an imperfect seal on the repeat-element behavior. In this study, simulation is used to investigate the effects of an imperfect seal behavior on the performance and reliability of SOFCs. Diffusion through the sealing material and inherent local combustion of fuel are added to the computational fluid dynamics (CFD) repeat-element model, which also allows us to compute the flow field, the electrochemical reactions, and the energy equations. The results are in good agreement with experiments. The zones of parasitic combustion and local overheating are well reproduced. Furthermore, the model predicts a risk of reoxidation under polarization that is well observed. The model also shows the necessity to take into account the diffusion transport for the development of compressive seal materials, hence verifying the hypotheses made by other groups. The modeling approach presented here, which includes the imperfections of components, allows us to reproduce experiments with good accuracy and gives a better understanding of degradation processes. With its reasonable computational cost, it is a powerful tool for a design of SOFC based on reliability.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Htceramix R design short stack. The active area is 50cm2 per cell.

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Figure 2

Gas manifold. (A) Fuel manifold and corresponding simulated flowfield. (B) Air manifold and corresponding simulated flowfield. (C) Detail of the stack manifold.

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Figure 3

Electrochemical model: equivalent circuit approach

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Figure 4

Simulated OCVs with varying porosity parameters: (●) with Knudsen correction; (◇) without Knudsen correction

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Figure 5

Set of porosity parameters for an effective diffusion coefficient Deff=4.90×10−4m2s−1 for hydrogen

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Figure 6

Diffusion through the seal next to the fuel inlet hole. Simulated hydrogen fraction and cell after operation. The red line is the redox limit.

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Figure 7

Local temperature elevation of lateral seals. Comparison of measured value and simulation output.

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Figure 8

Damaged air outlet on short stack MS 95 after operation (left). Simulation of the local overheating due to a parasitic flame for one repeat element (right).

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Figure 9

Redox front on the anode predicted by simulation at OCV (red) and at 30A (blue). Comparison with used cell of test MS 95 (right).

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Figure 10

(A) Cracks due to redox cycles under the lateral seals. (B) Sintered Ni microstructure due to high-temperature combustion of hydrogen under the seal.

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Figure 11

Degradation of the cathode due to diffusion of hydrogen through the internal seal on the cathode side. Mole fraction of hydrogen.

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Figure 12

Test MS95: degradation of performance with load cycling during long-term testing (800°C, 0.4nl∕minH2+3%H2O)

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Figure 13

Test MS95: measured (—) and predicted (●) electrochemical performance; predicted oxidized area in the reacting zone (×), and under the seals (▵)




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