Chart 1

"Clean Energy for the 21^st Century"

	AFC Alkaline Fuel Cell	PEM Proton Exchange Membrane Fuel Cell

Current Density	300 - 600 mA/cm²	600 mA/cm²
Voltage per cell	0.8 - 0.85V	0.65 - 0.70V
Power Density + accessories	50 kW/ 300kg 50 kW/ 400kg	50 kW/ 200 kg 50 kW/ 400 kg
Lifetime operation mode:
Continuous
Continuous	4000 hours	est. 5000 hours**
Intermittent	over 4000 hours (≈ 200,000 miles)	Unknown Unknown

Cost per kW + accessories	100 - 150 $ 200 - 300 $	500 - 1000 $ 1000 - 2000 $
Catalysts Anode Cathode	Nobel Metals No Nobel Metals	Nobel Metals Nobel Metals
Recoverability after misuse	High	Low

Maximum fuel impurities
Carbon monoxide (CO)	Not Critical	< 10 ppm
Carbon dioxide (CO₂)	< 100 ppm	Not Critical
Ammonia (NH₃)	Not Critical	Very Critical

Power Density (kW/L)	1.96*	1.75**
Specific Power (kW/kg)	2.40*	1.25**

*Based on current density for 400 mA/cm²

**Based on published reports

The AES Propulsion Fuel Cell (AFC) is less expensive and less complicated than the PEM Fuel Cell. The AFC does not require an air compressor for supplying air to the stack and does not need a humidifier to assure proper moisture content in the membrane. The AFC Fuel Cell is programmed to automatically remove the electrolyte from the stack while the fuel cell is not in operation, thus extending the life of the electrodes. The electrolyte in the PEM fuel cell is immobilized in the membrane and remains in the membrane even while the fuel cell is not in operation, thus leading to the degradation of the electrodes and damage due to parasitic currents.