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Research Papers

The Current Density Distribution in a Segmented-in-Series SOFC

[+] Author and Article Information
B. A. Haberman

The Department of Mechanical Engineering,  Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, UKb.haberman.01@cantab.net

A. J. Marquis

The Department of Mechanical Engineering,  Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, UKa.marquis@imperial.ac.uk

J. Fuel Cell Sci. Technol 6(2), 021003 (Feb 23, 2009) (7 pages) doi:10.1115/1.2971047 History: Received March 17, 2007; Revised March 18, 2008; Published February 23, 2009

A common tubular solid oxide fuel cell (SOFC) design consists of segmented-in-series electrochemical cells fabricated onto the outside of a porous support tube. Predicting the performance of this type of SOFC requires a detailed understanding of the current density distribution within each cell. This distribution is strongly coupled to the activation, concentration, and Ohmic losses, which occur as a result of the physical transport processes within the cell. A new computer code, known as the SOHAB code, has been developed to simulate these physical processes and thus make predictions of cell performance. The simulation results show how the magnitude of each loss varies spatially within the cell, causing the calculated current density distribution to be very different from that predicted by the established purely Ohmic models. At low currents the cell behavior is dominated by activation losses producing a very flat distribution. At moderate currents the Ohmic losses become more important, and the distribution is peaked at the edges of the electrolyte. At high currents the increased concentration losses flatten the distribution in the middle of the cell but not near its edges where gases flow from the surrounding inactive regions and the losses remain small. At low and moderate currents, the calculated current density distribution is sufficiently flat that the assumption of a uniform distribution can be used in conjunction with a one-dimensional model. However, at high currents this simplified model overestimates the concentration loss as it cannot account for the improved mass transport near the electrolyte edges.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Gas and ion transport and electrochemical reactions in a SOFC

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Figure 2

The Rolls Royce Fuel Cell Systems Ltd. IP-SOFC

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Figure 3

Cross-section through a row of segmented-in-series cells

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Figure 4

Conventional current flow path analyzed in Refs. 7-8

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Figure 5

Cross-section through the computational domain (all dimensions are in millimeters)

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Figure 6

Diagram showing a computational cell and the storage of information

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Figure 7

The calculated current density i distribution along the width of the electrolyte obtained for different computational grid resolutions

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Figure 8

The variation of each cell loss mechanism with applied current density, calculated separately

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Figure 9

Vectors of conventional current density plotted in the x-y plane of the cell

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Figure 10

A comparison between the current density distributions predicted by the SO-HAB code and a purely Ohmic model. The spatial variation of the potential difference across the electrolyte Ee is also shown.

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Figure 11

Hydrogen mole fraction XH2 distribution plotted in the x-y plane of the cell

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Figure 12

The spatial variation of concentration ΔEC and activation ΔEA losses along the width of the electrolyte

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Figure 13

Comparison between the current density distributions obtained at different mean electrolyte current densities

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Figure 14

Comparison between the normalized current density distributions obtained at different mean electrolyte current densities

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Figure 15

The variation in calculated cell output voltage with mean current density drawn through the electrolyte imean. A comparison is also made to the result obtained using the one-dimensional (1D) model described in Sec. 6.

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