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SOFC Numerical simulation of tubular SOFC based on electrode microstructural parameters

Satoshi USUI, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo Mina NISHI, The University of Tokyo Naoki SHIKAZONO, The University of Tokyo Nobuhide KASAGI, The University of Tokyo

Numerical simulation of tubular SOFC is conducted using electrode microstructural parameters. Layers of cross-sectional images are obtained using dual-beam focused ion beam­scanning electron microscope (FIB-SEM), and three-dimensional structure is reconstructed. Microstructural parameters such as tortuosity factor and porosity are calculated, and applied to the one-dimensional model. Gas transport is modeled using Dusty Gas Model (DGM). Fuel with a mixture of methane, hydrogen and steam is used, and the cell performance is compared with the experimental results. I-V (current-voltage) curves of both experimental and numerical results show the same trend when S/C (steam-carbon ratio) is varied. It is found that the average pore diameter and tortuosity factor have major effects on the concentration overpotential. Key Words: SOFC, Microstructure, FIB-SEM, Methane, Reforming reaction

Solid Oxide Fuel Cell: SOFC 3.2

(2)

(1) SOFC

Butler-Volmer (1) io io deBore (4) E (2) (1) (3) (4) Dusty Gas Model

2F (1- )2F ireac = i0 LTPB exp( act ) - exp(- act ) RT RT

ireac SOFC Three Phase Boundary: TPB TPB

Costamagna & Honegger(3)

E - act = io - el

(3) (4) (2) diel di = - io = ireac dx dx

d io d = iio io,eff , el = iel el,eff dx dx

Focused ion beam-scanning electron microscope: FIB-SEM

(1)

130

FIB-SEM(Carl Zeiss, NVision40) 1 pixel = 28.2 nm 31.6 nm Ni, YSZ 100 nm Voxel

(2)

(5) Table 1 Anode Structural Parameters Properties Value 3D-TPB density [1012 m/m3] 1.93 Average pore diameter [10-6 m] 0.75 Pore 3.19 Tortuosity YSZ 4.01 factor Ni 5.80 Pore 31.9 Volume YSZ 35.9 fraction Ni 32.2

3

1 . 3.1

Ni + Di,k

n

j=1, ji

y j N i - yiN j Di, j

=-

p dy i RT dz

(5) Evans (6)

(5)

Di,k

Knudsen

kT 0.5 d p Dk = 2m 1- 4(1+ /8)

dp k Graham

m

(7) M

1 1 1 1 y1 Deff = + + (1- y 3 ) - - D1,k D13 D12 D13 D12

-1

Table 2 Operating Conditions Operating conditions Value Temperature T [K] 1023 Pressure p [Pa] 1.013×105 H2 20 Exp. 1 H2O 0, 1.5, 3, 6 Fuel N2 10, 8.5, 7, 4 composition H2 5.0 [sccm] Exp. 2 H2O 5.0, 10.0, 15.0, 20.0 CH4 5.0 S/C (Steam Carbon Ratio) 1, 2, 3, 4

1.2 1.0 0.8 0.6 0.4 0.2

(8)

(9)

Voltage [V]

Bird

-2

(6)

Di,j (10)

0.0 0.0

0.2

0.4 0.6 0.8 2 Current Density [A/cm ]

1.0

1.2

T 3 (M + M ) / M M 0.5 { i j i j} Dij = 1.8829 ×10 2 P ij D

3.3

(7)

Fig.1

1.2 1.0 0.8 0.6 0.4 0.2 0.0 0.0

I-V curve of hydrogen experiment

(11) (12) CH 4 + H 2O 3H 2 + CO

H o = 206.2kJ/mol 298K H o = -41.0kJ/mol 298K

(11) (12)

CO + H 2O H 2 + CO 2

(8)

Voltage [V]

0.2

0.4 0.6 0.8 2 Current Density [A/cm ]

1.0

1.2

0.38 0.06 -50338 rCH 4 = 9.76exp ( pCH 4 ) ( pH 2 O ) RT

Fig.2 I-V curve of methane experimen (13) (NEDO)

2

1 (1) Shikazono, N, Sakamoto, Y., Yamaguchi, Y. and Kasagi, N., J. Power Sources, Vol. 193, pp. 530-540 (2009). (2) Iwai, H. et al., submitted to J. Electrochem. Soc., (2009).P. (3) Costamagna et al., Electrochimica Acta, Vol.43 Nos3-4 (1998), 375-394. (4) B.De Boer, SOFC Anode, Ph. D. thesis, Univ. of Twente, The Netherland (1998) (5) Evans et al., J. Chemical Physics, Vol. 35, No. 6, 2076-2083 (1961) (6) Bird, R.B., Steward, W.E. and Lightfoot, E.N., 2002, Transport Phnomena 2nd Ed., Wiley. (7) (8) , , , 14 , pp. 193-194 (2009).

2 S/C

SOFC

S/C

Information

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