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RESEARCH PAPERS: Fuel Cells

Electrochemical and Transport Phenomena in Solid Oxide Fuel Cells

[+] Author and Article Information
P. W. Li

Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA 15261

M. K. Chyu

Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA 15261mkchyu@engr.pitt.edu

J. Heat Transfer 127(12), 1344-1362 (Aug 23, 2005) (19 pages) doi:10.1115/1.2098828 History: Received May 07, 2004; Revised August 23, 2005

This paper begins with a brief review of the thermodynamic and electrochemical fundamentals of a solid oxide fuel cell (SOFC). Issues concerning energy budget and ideal energy conversion efficiency of the electrochemical processes in an SOFC are addressed. Chemical equilibrium is then discussed for the situations with internal reforming and shift reactions as an SOFC is fed with hydrocarbon fuel. Formulations accounting for electrical potential drops incurred by activation polarization, ohmic polarization, and concentration polarization are reviewed. This leads to a discussion on numerical modeling and simulation for predicting the terminal voltage and power output of SOFCs. Key features associated with numerical simulation include strong coupling of ion transfer rates, electricity conduction, flow fields of fuel and oxidizer, concentrations of gas species, and temperature distributions. Simulation results based primarily on authors’ research are presented as demonstration. The article concludes with a discussion of technical challenges in SOFCs and potential issues for future research.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

The ideal efficiencies of fuel cells and heat engines

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Figure 2

Principle of an SOFC

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Figure 3

Schematic view of the over-potentials in an SOFC

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Figure 4

Structure of a planar SOFC

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Figure 5

Structure of a tubular SOFC

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Figure 6

Discretization of current conduction in electrodes for a tubular SOFC

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Figure 7

Multi-physics coupling for SOFC modeling

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Figure 8

Illustration of the computation domain for a tubular SOFC

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Figure 9

Computation flow chart for simulation of SOFCs

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Figure 10

Results of prediction and test for cell voltage versus current density. (Operating pressures of the cells tested by Hagiwara (72) and Hirano (55) are 1.0atm, and that by Tomlins (6) is 5atm.)

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Figure 11

Effect of operating pressure on the cell voltage and power: (a) cell voltage and (b) cell power

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Figure 12

Longitudinal temperature distribution in a fuel cell

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Figure 13

Utilization percentages of species versus current density for SOFCs of different diameters (pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2; UH2 of 85% and UO2 of 17% for each SOFC)

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Figure 14

Cell voltage and power versus current density for SOFCs of different diameters (pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2, UH2 of 85% and UO2 of 17% for each SOFC)

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Figure 15

Variation of cell temperature with current density for SOFCs of different diameters (pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2; UH2 of 85% and UO2 of 17% for each SOFC)

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Figure 16

Cell voltage versus current density at different lengths of the cell tube (pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2; UH2 of 85% and UO2 of 17% for each SOFC)

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Figure 17

Cell temperature versus current density at different lengths of the cell tube (pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2; UH2 of 85% and UO2 of 17% for each SOFC)

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Figure 18

Cell tube temperature distribution with variation of cell voltage (the cell in Table 6 with a length of 1500mm; pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2; UH2 of 85% and UO2 of 17%)

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Figure 19

Cell voltage versus current density at different oxygen stoichiometries (the cell in Table 6 with a length of 1500mm; pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2; UH2 of 85% and UO2 of interest)

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Figure 20

Variation of cell temperature with current density at different oxygen stoichiometries (the cell in Table 6 with a length of 1500mm; pair=pf=1.013×105Pa; Tf=900°C; Tair=600°C; flow rates are set constant at an average current density of 600mA∕cm2; UH2 of 85% and UO2 of interest)

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Figure 21

Variation of flow rate in a tubular SOFC without reforming (the cell in Table 6 with a length of 1500mm; pair=pf=1.013×105Pa; Tf=800°C; Tair=600°C; current density of 300mA∕cm2; UH2 of 85% and UO2 of 17%)

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Figure 22

Variation of flow rate in a tubular SOFC with reforming (the cell and operating conditions in Table 9; current density=450mA∕cm2)

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Figure 23

Local mass fraction distributions of gases in a tubular SOFC with internal reforming (the cell and operating conditions in Table 9; current density=450mA∕cm2)

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Figure 24

Voltage and power of a planar type SOFC (with dimensions and operating conditions given in Tables  78; flow rate of fuel and air vary with the current density at UH2 of 85% and UO2 of 20%)

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Figure 25

Local mass fraction distributions of gases in a planar SOFC with internal reforming: (a) Hydrogen and (b) Oxygen (with dimensions and operating conditions given in Tables  78; current density=600mA∕cm2)

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