New Interconnections for Planar Alloy-Separator Sofc Stacks
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Mat. Res. Soc. Symp. Proc. Vol. 496 01998 Materials Research Society
Fig. 1 Conceptual drawing of a CE stack. The air electrode is connected with the separator edge, in the outside of the air compartment of the cell.
, ... o• o0Qqo0 o.... o... Fuel
•7 Air Fig. 2
Schematic drawing of square planar AES cells which are stacked with the proposed interconnections.
206
-Insulator sheet
Fig. 3
Schematic diagram of a CE stack showing the current in air electrodes, Ni - felt interconnections and alloy separators.
Fig. 4 Schematic diagram showing sliding seals and Ni - felt flexible interconnections in a CE stack.
207
Estimation of IR potential drops in a side-lead cell We calculate the IR potential drops in an LSM support acting as an air electrode in a CE stack. The calculation was made with a planar disk cell having a LSC ring shown in Figs.5a and 5b. The diameters of the fuel electrode, LSM support and LSC ring are indicated as dA, d., and dc, respectively. The thicknesses and the resistivity of YSZ electrolyte, LSM support and LSC ring are assumed to be 4.OxlO 4 mm, 3.0mm and 5.0mm, and 10.OQcm, 5.Oxl0WQcm and 2.5xlO-2 Qcm, respectively. The porosity of the LSM is 33.3%. Figure 5c shows the circuit model used in the calculation. Points A, B, C and D indicate fuel electrode, the edge of the active area of the cell, the edge of the LSM support and the edge of the LSC ring, respectively. Resistors r r and r,1, r.2, ... represent the resistances of the small segments of electrolyte, and those of ISM support, in the active area of the cell. Resistors r,,(, and rcD indicate the resistances of LSM and LSC rings, respectively. The results of the calculation for dA = 192mm, dM = 200mm and dc = 210mm are in Table I. The potential drops for the current 2
density of 300mA/cm in the active area are also listed in the table. The calculation of the resistance r. was made according to a model of a solid LSC ring, therefore a relatively high potential drop of 28.7mV was derived. We can reduce this potential drop by extending the edge of the LSM support into the LSC interconnecting ring, as it is shown in Fig.3. It is assumed that the resistance of the junctions between the Ni coated LSC and the alloy separator is much lower than the resistances described above. In the following section, we reduce the resistance of the junctions between Ni felts and alloy separators.
LSM LSC Fuel electrode
D
CB
dA
(a)
dMm dc
(b) o-A
D Cpl Br2r rCD rBc
r.1
PM
r.2 (C)
Fig. 5 A disk cell with a LSC connecting ring, used in the calculation of IR losses in the proposed cell stack; (a) side view, (b) top view, (c) equivalent circuit.
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Table I Resistances calculated for the segments in the model shown in Fig. 5, and the potential drops for the current density of 300mA/cm 2 in the active area of the cell.
IRdrop for 300mA/cm 2 (mV)
Resistance (Q) rAB
1.38 X 10-4
12.0
rBc
1.62 x 10-4
14.1
3.3 x 10-4
28.7
rc
REDUCTION IN THE RESISTANCE OF THE JUNCTIONS BETWEEN HEAT RESISTANT ALLOYS AND NICKEL FELT Reduction in the resist
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