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0 5 10 15 20 25 30 Current, I/A Fig. 5 I-V characteristics after thermal cycles o initial a after 1 thermal cycle -» after 2 thermal cycles a after 3 thermal cycles x after 4 thermal cycles + after 5 thermal cycles o initial a after 1 thermal cycle -» after 2 thermal cycles a after 3 thermal cycles x after 4 thermal cycles + after 5 thermal cycles

Figure 5 shows I-V characteristics after performing five thermal cycles to ambient temperature. Degradation of the stack performance can be scarcely observed. 3.3 Two units (10-cell stack)

The performance of 10-cell stack using two units is showed in Figure 6. The maximum power was 294 W (the power density was 0.25 Wcm'2), and terminal voltage at 0.3 Acm"2 was 6.88 V. Since the power density was comparable to that of single cell, the decrease of the stack performance by assembling single cells was considered small.

Figure 5 shows I-V characteristics after performing five thermal cycles to ambient temperature. Degradation of the stack performance can be scarcely observed. 3.3 Two units (10-cell stack)

The performance of 10-cell stack using two units is showed in Figure 6. The maximum power was 294 W (the power density was 0.25 Wcm'2), and terminal voltage at 0.3 Acm"2 was 6.88 V. Since the power density was comparable to that of single cell, the decrease of the stack performance by assembling single cells was considered small.

Fig. 6 I-V/P characteristics of 10-cell stack

4.Conclusion

OG type cell stack appear its good thermal cycle performance, and there is little decrease of the power density if they are stacked to 10 cells. Because each cell are connected electrically by Ni felt, the load of upper cell does not put on the lower cells, and thermal stress by deformation of each cells while the stack are heated and cooled may be released. That attribute the good performance of the cell stack.

5 .References

(1) K.Akagi, Proc. of the 34th Battery Symp. in Japan, Hiroshima,pp,167-168(1993)

(2) K.Akagi, Extended Abstracts of the 2nd Symp. on SOFC in Japan, Tokyo, pp.33-36(1993)

(3) K.Akagi et al. Proc. of The 1st FCDIC Fuel Cell Symp., Tokyo, pp.300-303(1994)

(4) A.Shiratori et al. Program and Abstracts of Fuel Cell Seminar in SanDiego CA, pp.37-40(1994)

(5) A.Shiratori et al. Proc. of the 4th Interntl Symp. on SOFC, pp.255-263(1995)

(6) K.Akagi et al. Proc. of the 2nd IFCC in Japan, Kobe, pp.239-242(1996)

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