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confidentialwww.solidcell.com 1
SolidCell
Composite Interconnect for SOFC
Sergey Somov1, Olivia Graeve2, Sam Ghosh3, and Heinz Nabielek1
1 Solid Cell Inc., 771 Elmgrove Rd., Rochester NY 14624
2 Alfred University, 2 Pine St., Alfred NY 14802
3 RocCera LLC, 771 Elmgrove Rd., Rochester NY 14624
Daytona Beach, January 25, 2012
confidentialwww.solidcell.com 2
SolidCell
The Interconnect as a Key Component
Metallic-based
Advantages•High mechanical strength & plasticity •High electric conductivity•High thermal conductivity
Disadvantages•Formation of oxide scale in air•Poisoning of cathodes by chromium from stainless steel
Oxide-based
Advantages•Stability in air & fuel •Mechanical stability at high temperatures
Disadvantages•Fragile ceramic materials•Changes in dimensions from variation of oxygen activity
Traditional materials
confidentialwww.solidcell.com 3
SolidCell
Composite Interconnect
A combination of oxide and metallic materials produces a composite with high temperature stability, mechanical robustness, high electrical conductivity, and an adjustable coefficient of thermal expansion (CTE). Also, it withstands corrosion.
The general interconnect composition is:
xNi + (1 – x – y)TiOxNi + (1 – x – y)TiO22 + yNb + yNb22OO55
confidentialwww.solidcell.com 4
SolidCell
Composite Interconnect
The general interconnect composition is:
xNi + (1 – x – y)TiOxNi + (1 – x – y)TiO22 + yNb + yNb22OO55
•Oxide components provide strength and corrosion resistance
•Metallic component increases electrical conductivity and plasticity
confidentialwww.solidcell.com 5
SolidCell
Oxide Component of the Composite
Titania doped by niobium oxide has high electrical conductivity in fuel and moderate conductivity in air.
0,85 0,90 0,95 1,00 1,05
1E-3
0,01
0,1
1
10
100
I52 (5% Nb2O
5) - Air
I52 (5% Nb2O
5) - H
2
I56 (7% Nb2O
5) - H
2
I56 (7% Nb2O
5) - Air
I44 (7% Nb2O
5) - H
2, S
m*c
m-1
1000/T
confidentialwww.solidcell.com 6
SolidCell
Thermal Expansion
y = 0,00000968x - 0,00015892
y = 0,00000918x - 0,00011143
y = 0,00001017x - 0,00018005
y = 0,00000986x - 0,00009899
0
0,001
0,002
0,003
0,004
0,005
0,006
0,007
0,008
0,009
0 200 400 600 800 1000
Т, 0С
(L-L
0)/
L0
33,5%
35,3%
37,2%
YSZ
9,0
9,2
9,4
9,6
9,8
10,0
10,2
10,4
33 34 35 36 37 38
%NiC
TE*1
06 , K
-1
Influence of Ni content on thermal expansion
Dependence of CTE on Ni content at 850oC
confidentialwww.solidcell.com 7
SolidCell
Supporting High Conductivity on the Cathode Side
air
H2
Interconnect disc
YSZ tube
0
0,01
0,02
0,03
0 100 200 300 400
time, hrs
Rs,
Oh
m*c
m2
hydrogen replacement by air
Slight IC porosity provides penetration of hydrogen and keeps the composite in reduced state
confidentialwww.solidcell.com 8
SolidCellChanges of TiO2 (Nb2O5) Resistance
After Replacement of the Gas Environment
11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:12
0
25
50
75
100
125
150
175
I56 H2 to Air
I44 Air to H2
I44 H2 to CO
2
R,
Ohm
t
a)
The slow change of the resistance is explained by an extremely low rate of oxygen diffusion into doped titania.
18:00 27:00 36:00 45:00 54:00 63:00
0,5
1,0
1,5
2,0
2,5
3,0 I56 H
2 to Air
I44 Air to H2
I44 H2 to CO
2
I44 CO2 to Air
R,O
hm
t
Change of gas environment from air to hydrogen and back: a) –short time; b) –long time
b)
confidentialwww.solidcell.com 9
SolidCell
Composite Interconnect in the MPC Stack
confidentialwww.solidcell.com 10
SolidCell
Composite Interconnect in the MPC Design
confidentialwww.solidcell.com 11
SolidCell
Conclusion
The novel composite interconnect consisting of nickel and titania doped by niobium oxide has high mechanical strength, and high electrical conductivity in air and fuel.
It withstands thermal cycling and oxidation by air.
The coefficient of thermal expansion may be adjusted by variation of the metallic and oxide component ratio.
Acknowledgements: This work was co-funded by NYSERDA (Project No 23644).
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