Fuel Cells for UAVs

DOD Wants U.S. Solid Fuel Source For Fuel Cells

The U.S. Defense Department wants to establish a domestic production capability for alane, a solid fuel that can be used in fuel cells that generate electricity to power a wide range of applications from wearable electronics to aircraft systems.

“Military systems of today and tomorrow are eclipsing the limits of batteries,” says a U.S. Air Force Research Laboratory (AFRL) solicitation seeking proposals to establish a manufacturing capability for high energy-density alane fuel.

Alane, or aluminum hydride, stores hydrogen that can be controllably released by heating to feed a fuel cell. The project, under Title III of the Defense Production Act (DPA), will support a path toward mass production and cost reduction for stable crystalline alane, also known as alpha alane.

Hydrogen fuel cells offer high energy density with simple refueling and enable longer mission times compared with rechargeable batteries. “While the military investigated many different hydrogen sources, the one that has stood out as the most promising and able to fit in our logistic structure is alane,” the solicitation says.

Alane was developed in the 1960s by both the U.S. and Soviet Union under secret projects to produce a high-energy rocket fuel. In 2016, HRL Laboratories proposed using an alane fuel cell to power unmanned aircraft.

According to HRL, an alane cartridge weighing 280 grams (less than 10 oz.) could provide the same flight time as 3 kg of lithium-ion batteries or 980 grams (2.15 lb.) of gaseous hydrogen stored at 4,500 psi. The Pentagon also has tested wearable alane fuel cells produced by Ardica.

According to AFRL, alane’s advantages are high energy content for a small weight and volume, safe and simple usage, long shelf life and minimal environmental impact–hydrogen fuel cells emit water vapor. Alane contains 10% hydrogen by weight and has twice the volumetric energy density of liquid hydrogen.

The disadvantages have been that producing alane has required large quantities of raw materials and large amounts of energy to produce small amounts.

But companies such as Ardica claim to have developed more efficient methods that reduce the feedstock and energy required to produce the fuel.

“The significant disadvantage of alane is the lack of any large-volume commercial production capacity,” the solicitation says. The fuel has been synthesized at costly laboratory scale, but has not been transitioned to mass production to reduce its cost.

The plan is to use DPA Title III funding to support development and construction of a pilot line that will prove out the capability to produce alane at a small production-representative scale. This line will provide the government with information on the requirements for scaling up production.

AFRL plans to make up to two awards worth $2 million, each matched by $2 million in contractor cost sharing. Bidders must detail how they plan to reduce the costs or volumes of raw materials and increase production to meet viable target fuel costs for military and commercial applications.

–Graham Warwick, warwick@aviationweek.com