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(a) äneasuieäaias-siiteiEdlxdy.

(b) 9neaauEdatrocm tonp.afterH2 xoductbn (an4/$ Etec).

(c) pflqiiprt atlOOQ jnH 2 atmosphere.

(d) On are iini afterH 2 laäuctpn ii aoooKianosw ith ttuE&poiitbendiig test.

(a) äneasuieäaias-siiteiEdlxdy.

(b) 9neaauEdatrocm tonp.afterH2 xoductbn (an4/$ Etec).

(c) pflqiiprt atlOOQ jnH 2 atmosphere.

(d) On are iini afterH 2 laäuctpn ii aoooKianosw ith ttuE&poiitbendiig test.

(2) Fabrication of single cell

A tubular flat plate was made by extruding the anode material described above. The size of this sintered plate was 40 x 100 x 5 (w-1 -t :mm).

The electrolyte and interconnection were deposited as a 200-pm layer by plasma spraying the raw powders. The number of plasma sprays and the spraying distance were carefully selected, because the density of the sprayed layer is related to these conditions. Commercial YSZ powder was used for the electrolyte and La(Ca)CrO, powder for the interconnection layers. The thermal expansion coefficient of the interconnection was controlled to 10 xl0'6(l/K) by varying the ratio of Ca in the powder. The value of this coefficient is almost the same as that of YSZ . The conductivity of interconnection material was 30 S/cm in the ambient atmosphere, and I S/cm in a hydrogen atmosphere of at IOOO°C. The gas permeability coefficient of the electrolyte layer was 7xl0'6 (cm4/ g-sec), and that of interconnection was 2x10"'(cm4/g-sec). An air clcctrodc was made from La(Sr)MnO, by slurry coating. The air electrode was 50pm thick, and its surface area was 6 cm2. The external appearence of a single cell is shown in Fig. 3.

Fig. 3 External appearance of a single tubular flat-plate SOFC cell

4.1-V/P CHARACTERISTICS OF THE STACK

A stack was composed by placing cells in a stack holder made from alumina, and sealing the ends of cells and joints of the holder. Electrical contact between cells was made with a Pt mesh. Generation tests were carried out successfully on this stack at 1000'C by supplying hydrogen and oxygen gas to each inlet gas manifold. Figure 4 shows the I-V/P characteristic's. The open circuit voltage of a single cell was 0.85 V, which is lower than the theoretical value. This is thought to be caused mainly by insufficient density of the YSZ layer. Gas leakage at the side of the single cell might be another cause. Notwithstanding this open circuit voltage, the stack showed faily good characteristics and the voltage loss was small. According to an analysis of the voltage drop, this loss was caused by the resistance of the YSZ layer, and partly by the electrode activity and contact resistance. The maximum output power density of this stack was 0.35 W/cm2. This power density has proved the usefulness of the concept of the cell and stack of Tubular Flat-Plate SOFC.

In the near future, we expect to improve the density of the electrolyte layer, which should improve the cell characteristics. Then output power of the stack will also be increased by increasing the number of cells.

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