The system uses a fine metal powder to absorb hydrogen gas under high pressure. When the powder absorbs hydrogen, it becomes a "metal hydride," and the process is called "hydriding." By then decreasing the pressure in the vessel or warming the metal hydride, the hydrogen can be released to drive a fuel cell or engine.
A complication in perfecting the technology, however, is that the hydriding process generates heat, which hinders the absorption process and prevents the hydrogen storage vessel from being filled rapidly, says Issam Mudawar, a Purdue Univ. professor of mechanical engineering who leads the work with research assistant professor Timothée Pourpoint and doctoral student Milan Visaria.