Fig. 4. Schematic diagram of the apparatus for testing the fuel cell. cell having an active area of 25 cm2. The terminal voltage was measured at each dew point of gaseous hydrogen of 68, 70, 72 and 75°C, and test results are shown in Fig. 6. At the dew point of 68°C, the terminal voltage exhibited ripply behavior. This phenomenon means the asbestos matrix is dry. At the dew point of 75°C, the terminal voltage dropped within one hr, and leakage of electrolyte solution into the gas chamber was observed. In this case, the asbestos matrix is excessively wet. At the dew points of 70°C and 72°C, the terminal voltage was very stable. Therefore, these results indicate that water balance of the experimental cell can be achieved only with very severe control of the humidity of feed gaseous hydrogen. Effect of humidity of gaseous hydrogen and operating temperature on discharge characteristics. Since the humidity control should be closely related to the variation of operating temperature, the relativity of these two control parameters was examined by the test shown in Fig. 7. This test proved that the asbestos matrix became excessively wet at the dew point of 72°C and at an operating temperature of 78°C (case 1, Fig. 7), and dry at the dew point of 68°C and at an operating temperature of 82°C (case 3, Fig. 7). Comparison of Fig. 6 and Fig. 7 indicates that the operating temperature of the cell, as well as the dew point of feed gaseous hydrogen, should be controlled within the narrow range of ± 1°C. However, this tolerance limit is possibly widened if the feed rate of gaseous hydrogen is increased beyond 5 x of the theoretical consumption rate. Effect of operating pressure on discharge characteristics. The ultimate operating pressure of the cell stack is planned as an operating pressure of 0.4 MPa (4 Atm). A
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