Hydrogen Fuel Cells for Small Unmanned Air Vehicles

The Naval Research Laboratory has been researching the use of hydrogen fuel cells for propulsion of long-endurance unmanned air vehicles (UAVs) for military and civilian applications.  The high electrical efficiency of polymer electrolyte fuel cells (PEFCs) in combination with the high energy content of hydrogen enable the long endurance flights.  The systems also offer the numerous attractive attributes of electric power, including instant starting, ease of control, near-silent operation, rapid load response, and high quality electric power. 

The progression of Ion Tiger flights will be discussed.  Ion Tiger used a ~ 1 kg 550-W (0.75-horsepower) fuel cell system from Protonex Technology Corporation with 0.5 kg of compressed H₂ in a 4-kg a carbon/aluminum pressure vessel to fly for 24 hours continuously in Nov 2009.  The vehicle also carried a 5-lb payload. In April 2013, the Ion Tiger flew for 48-hours by using liquid hydrogen fuel in a new, NRL-developed, cryogenic fuel storage tank and delivery system.  These 1-day and 2-day demonstrations prove that hydrogen fuel cells provides a clear path to long endurance electric flight: in comparison, the Ion Tiger would be able to fly for only 4 hours on the comparable amount of lithium batteries.

This talk will discuss the scientific challenges related to using PEFCs in UAVs.  The most important criterion is weight, demanding a high power to weight fuel cell along with high efficiency to maximize the use of the on-board hydrogen.  Therefore, high activity, efficient electrocatalysis is needed, along with components with few I2R losses.  The system should ideally operate near 80 °C to minimize the need for heat rejection. We have also become cognizant of poisoning issues, specifically related to coolant leakage through carbon bipolar plates, and also issues related to airborne contaminants, such as SO2, and the NaCl in sea mist.

We are grateful for support from the Office of Naval Research.