Low Pressure Hydrogen Storage Technology
The typical commercially available means for storing hydrogen fuel is storage in special tanks at very high pressure (up to 6000
psi). Another feasible method is storage of cryogenic liquid hydrogen in vacuum-insulated tanks. A disadvantage of storage at high pressure is the weight of the tanks and the inability to store a large mass of fuel in a small space. Cryogenic storage has several disadvantages, including the need for special handling because of the very cold temperature. Current research at various laboratories is investigating the use of graphite nano-fibers (“carbon whiskers”) and other similar concepts. The fibers are typically 5 to 100 microns long, with a diameter of 5 to 100 nanometers, and are made up of stacks of platelets. The graphite substrate serves as an adsorbent, a “sponge” to store a large mass of hydrogen in a tank at low to moderate pressure. Pressurizing the tank during filling causes the substrate to adsorb the hydrogen molecules, and depressurization during use causes the hydrogen to be released. So far, results of tests using such substrates have been inconclusive, and the mass of hydrogen projected to be stored by these methods (mass of fuel per weight and volume of storage container) is not especially impressive.
We are working in a collaborative effort with a private-sector industrial partner in research and development of a technology that promises to greatly improve the effectiveness of graphite fibers for storing hydrogen at low to moderate pressure. The technology uses metal ions to intercalate graphite fibers to increase the adsorption area. Additional details about this promising technology are proprietary at this time.
If the technology proves to meet our expectations, it will help overcome one of the obstacles to widespread commercial use of hydrogen as a vehicle fuel: the difficulty of storing a large measure of hydrogen energy in a small, light-weight package.