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SPECIAL ISSUE RESEARCH PAPERS

Diffusion and Chemical Reaction in the Porous Structures of Solid Oxide Fuel Cells

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

Hopkinson Laboratory,  Cambridge University Engineering Department, Trumpington Street, Cambridge, CB2 1PZ, UKb.haberman.01@cantab.net

J. B. Young

Hopkinson Laboratory,  Cambridge University Engineering Department, Trumpington Street, Cambridge, CB2 1PZ, UK

J. Fuel Cell Sci. Technol 3(3), 312-321 (Jan 17, 2006) (10 pages) doi:10.1115/1.2211637 History: Received November 23, 2005; Revised January 17, 2006

The Rolls-Royce integrated-planar solid oxide fuel cell (IP-SOFC) consists of ceramic modules with electrochemical cells printed on the outer surfaces. The cathodes are supplied with oxygen from air flowing over the outside of the module and the anodes are supplied with fuel diffusing from the internal gas channels. Natural gas is reformed into hydrogen in a separate reformer module of similar design except that the fuel cells are replaced by a reforming catalyst layer. The performance of the modules is intrinsically linked to the behavior of the gas flows within their porous structures. The multi-component convective-diffusive flows are simulated using a new theory of flow in porous material, the cylindrical pore interpolation model. The effects of the catalyzed methane reforming and water-gas shift chemical reactions are also considered using appropriate kinetic models. It is found that the shift reaction, which is catalyzed by the anode material, has certain beneficial effects on the fuel cell module performance. The shift reaction enables the fuel cells to make effective use of carbon monoxide as a fuel when the supplied fuel has become depleted of hydrogen. In the reformer module the kinetics of the reaction make it difficult to sustain a high methane conversion rate. Although the analysis is based on IP-SOFC geometry, the modeling approach and general conclusions are applicable to other types of SOFCs.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 9

Diagram showing the one-dimensional computational domain which includes the porous support and active layers (anode for the fuel cell module and catalyst layer for the reformer module)

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Figure 1

Gas and ion transport, and electrochemical reactions in an IP-SOFC

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Figure 2

Schematic diagram of the Rolls-Royce IP-SOFC modules. The electrochemical cells and catalyst layers are printed on both sides of the ceramic module.

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Figure 3

Diagram of the fuel cell and reformer configuration

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Figure 4

Details of the porous structures of the fuel cell and reformer modules

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Figure 5

The counter diffusion of a binary gas mixture through a porous material

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Figure 6

The effect of an applied pressure difference on the counter diffusion of helium and argon through a porous specimen

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Figure 10

Pressure and temperature distributions within the porous layers of the fuel cell and reformer modules

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Figure 7

Hydrogen production rate Sr,H2, for the methane reforming reaction, calculated from Eqs. 16. The contour labeled “Equilibrium composition” corresponds to Kar=Kpr.

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Figure 8

Hydrogen production rate Ss,H2 for the water-gas shift reaction, calculated from Eqs. 17. The contour labeled Equilibrium composition corresponds to Kas=Kps.

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Figure 11

(a) Variation of mole fractions and non-equilibrium ratio Kas∕Kps in the fuel cell module (shift reaction suppressed). (b) Variation of mole fractions and non-equilibrium ratio Kas∕Kps in the fuel cell module (shift reaction included).

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Figure 12

Variation of Kas∕Kps at the ASI (anode-support interface) as a function of Kas∕Kps in the fuel channel. Suppressing the electrochemical reaction reduces the departure from shift equilibrium and the hydrogen production rate.

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Figure 13

Variation of the Nernst potential EN calculated for the gas conditions in the fuel channel and at the AEI (anode-electrolyte interface) as a function of Kas∕Kps in the fuel channel

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Figure 14

Variation of the effective CO‐H2 molar utilization ratio RCO∕H2 as a function of Kas∕Kps in the fuel channel

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Figure 15

Variation of gas species mole fractions in the reformer module

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Figure 16

Variation of Kar∕Kpr at the CSI (catalyst-support interface) as a function of Kar∕Kpr in the fuel channel

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