Air Transport

An alternative to pressure vessels for storing hydrogen fuel is being investigated under a US Air Force Research Laboratory (AFRL) contract with Massachusetts-based fuel-cell developer Protonex Technology. AFRL is seeking alternatives to batteries for long-endurance micro air vehicle (MAV) power generation.

Although fuel cells offer greater energy efficiency than batteries or combustion engines, their preferred energy source, hydrogen gas, requires double the volume as hydrocarbon fuels to deliver the same amount of energy and therefore requires bulky pressure vessels for storage. This is a problem for MAVs, which need to be lightweight.

An alternative storage method is hydride compounds, which absorb hydrogen gas into a solid structure. The gas is released with a simple chemical mechanism, often heat and/or water.

“[We] expect to achieve flight times of 8-12h,” says Protonex, which has an agreement with New Jersey-based Millennium Cell to use its sodium borohydride hydrogen delivery technology.