125

(After 100 hours operation at 600mA/cm2, 190'C , PH2/P02=100X/21X)

The Relation between the driving force and capillary force

In this section also were used the same configuration cells as the figure 1. Both A-Sub and F-Sub were not wet-proofed, and in A-RP was loaded acid of 17% AFL at the fabrication of the cell, not loaded in F-RP. Two kinds of F-RP were prepared for this test; the pore size of one F-RP (F-RP-1) was much smaller than that of each Sub, and that of the other one (F-KP-2) was bigger than that of F-EP-1 but a little smaller than that of each Sub. Two kinds of cells which used these F-RP were operated for 100 hours at 600mA/cm2 ( enough conditions to attain equilibrium state of acid distribution ) and then the AFL of each component was measured.

Figure 5 shows the final AFL after this operation. In both cases, the AFL of catalytic layers scarcely changed, that was, the capillary force which was composed by the particles of catalyst was stronger than the driving force. Same results were obtained under the load conditions of 300 and 150 mA/cm2 operation. Also the AFL of matrix didn't change and remained approximately 100%. It meant the capillary force of matrix was stronger than the driving force in the cell

The AFL of RP and Sub were as follows. When the F-RP-l was used, the AFL of F-Sub decreased to about 12%. Meanwhile with the use of F-RP-2, AFL of the F-Sub was about 24%. It is noted that these balances of the AFL between F-RP and F-CP was approximately in accordance with the balance which could be estimated by the pore size distribution of Sub and RP. Consequently the driving force was generated neither in F-Sub nor in F-RP.

On the other hand, the acid loaded in A-Sub and A-RP was transferred to anode and the AFL decreased almost to 0% in either case of F-RP-1 and F-RP-2. These results were also the same when operated at 300 and 150mA/cm2. Hence the driving force was stronger than the capillary force of A-Sub and A-RP.

Conclusion

We have revealed the dynamic distribution of electrolyte acid during a cell operation; the add loaded in A-RP and A-Sub is transferred to anode by a force other than the capillarity. The strengths of the driving force depends on the current density. In general the force is stronger than the capillaiy force of Sub and RP, but weaker than that of catalytic layers and matrix. The driving force is generated neither in F-Sub nor in F-RP. These results are useful for the design of phosphoric acid fuel cells.

Acknowledgment

The authors are sincerely grateful to Mr. Harasliima and Mr. Sugiyama for their useful suggestion, and to Mr. Tadano for his great assistance in the experiments.

References

(lyrMori, etal. J. Electrochem. Soc.; voL 135,1104 (May 1988) (2)R.Tanuma and H.Nishihara, "Electroosmotic electrolyte transport in phosphoric acid fuel cells" The 2nd International Fuel Cell Conference, February 5-8,1996, JAPAN.

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