Rt

where L is matrix thickness, 0a is electrolyte pore-filling ratio in - anode, 8C is electrolyte pore-filling ratio in cathode, Bc is electrolyte pore-filling ratio in matrix and se is void -space ratio of matrix.

More adequate equations with functions of operating time, temperature and partial pressures will be induced by basic cell operation under series of several accelerated conditions for approximately estimating longer lifetime of cell stacks improved and developed further.

6. Conclusion

MCFCs provide the opportunity for achieving higher system efficiencies operating under higher temperature condition around 650 "C because of the nature of electrolyte. Considering about future commercialization of MCFC power plants, we shall continue to devote to our research and development through international information exchange. Such issues including manufacturing cost shall be overcome after achieving our target in FY 1999.

This -research for longer lifetime cell has been conducted at New Sunshine Programme Headquarters in Agency of Industrial Science and technology, Ministry of International Trade and Industry. The substantial help and valuable comments on this paper from MITI as well as NEDO are gratefully acknowledged.

- 1. K. Tanimoto et al„ "Long Term Operation of the 100-cm2 class Single-Cell of MCFC", 2nd IFCC, p. 211, Feb. 1996

2. Y. Mugikura et al., "Shorting by Dissolution of NiO Cathode in MCFC", 2nd IFCC, p. 169, Feb. 1996

3. S. Mitsushima et al., "Modeling of Life for Molten Carbonate Fuel Cells", 2nd IFCC, p. 211, Feb. 1996

4. A. Tsuru et al., "Electrode's Deformation and Cell Performance on MCFC Stack", 2nd IFCC, p. 161, Feb. 1996

5. A. Sasaki et al., "Development of Internal Reforming Molten Carbonate Fuel Cell", 2nd IFCC, p. 131, Feb. 1996

6 M. Tatumi et al., "Current Status and Future Aspect of the Development of Long Life Cell", 2nd IFCC, p. 203, Feb. 1996

ENDURANCE TESTING WITH Li/Na ELECTROLYTE

Estela T. Ong, Robert J. Remick and Chakravarthy I. Sishtla Institute of Gas Technology 1700 South Mount Prospect Road Des Plaines, IL 60018-1804

Abstract

The Institute of Gas Technology (IGT), under subcontract to M-C Power Corporation under DOE funding, has been operating bench-scale fuel cells to investigate the performance and endurance issues of the Li/Na electrolyte because it offers higher ionicconductivity, higher exchange current densities, lower vapor pressures, and lower cathode dissolution rates than the Li/K electrolyte. These cells have continued to show higher performance and lower decay rates than the Li/K cells since the publication of our two previous papers in 1994.(1,2)

In this paper, test results of two long-term 100-cm2 bench scale cells are discussed. One cell operated continuously at 160 mA/cm2 for 17,000 hours with reference gases (60H2/20C02/20H20 fuel at 75% utilization and 30C02/70 air oxidant humidified at room temperature at 50% utlization). The other cell operated at 160 mA/cm2for 6900 hours at 3 atm with system gases (64H2/16C02/20H20 at 75% utilization and an M-C Power system-defined oxidant at 40% utlization). Both cells have shown the highest performance and longest endurance among IGT cells operated to date.

Results and Discussion

IGT Cell-934 operated continuously at 160 mA/cm2 for 17,000 hours (about 2 years) with reference gases, including one thermal cycle, with a decay rate of 2 mV/1000 hours. It reached a peak performance of 809 mV. Its performance lifegraph is shown in Figure 1. The thermal cycle occurred after about 6000 hours of operation: the cell was cooled down, clamped between flanges,and moved to another test facility where it was restarted. Toward the end of the 17,000 hours operation, cell performance had decreased to about 720 mV due to decreased anode wet seal efficiency and OCV and increased N2 crossover.

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