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Performance Requirements - The objectives of Phase I were to advance the performance, power density and economic viability of direct-hydrogen-fueled PEM fuel cell stacks for automotive propulsion, and fabricate a 10 kW stack to demonstrate the improvements achieved. The fuel cell stack performance requirements included the following:

1. Fueled with hydrogen gas and air,

2. Stack gross power output of approximately 10 kW when operating at 0.6 V per cell;

3. Catalyst loading of 0.25 mg/cm2 or less (total for cathode and anode together);

4. Stack power density of 3.63 kg/kW (8 lbm/kW), excluding auxiliary equipment, when operating with air supply pressure of308 kPa (30 psig) or less.

The considerably more stringent requirements for the Phase II power system presently under development by Mil are indicative both of the near term state of the technology and eventual automotive requirements:

1. Fueled with hydrogen gas and air;

2. System net power output of 50 kW when operating at 0.6 V per cell;

3. Catalyst loading of 0.25 mg/ cm2 or less (total for cathode and anode together);

4. System net power density of 1.82 kg/kW (4 lbm/KW), excluding auxiliary equipment (radiator, water pump, etc) when operating at air supply pressure of308 kPa (30 psig)orless;

5. Specific operating voltage range.

Design and Performance Development The overall development approach was to evaluate new concepts in laboratory size hardware and then to scale up to the lOkW size where they would be verified. The overall 10 kW stack specification is shown in Table 1. The cost reduction efforts were focused on the implementation of low Platinum loading catalyst technology for the membrane electrode assembly (MEA) by a technique that could be utilized in volume production. This task resulted in a manufacturing capability with throughput adequate for pilot production and yielded cells of 50 cm2 size with performance similar to that shown in Figure 2 for two different Platinum loadings.

The next step in the development process was to achieve comparable performance in much larger cells. As demonstrated in Figure 3, the overall cell performance target level of 800 ma/cm2 at 250 cm2 was easily reached. With the cell performance target reached, attention was turned to increasing the stack power density by increasing cell pitch. The final tested design was approximately 6 active cells per inch including the humidification and cooling/heating functions; however designs of 8 to 10 active cells per inch appear feasible in the near term.

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