This approach is designed to address storage life limitations, energy penalties, and/or weight penalties associated with liquid hydrogen, metallic hydride and high-pressure gas-phase hydrogen storage technologies.

In addition to those three general types of hydrogen storage noted above, researchers have explored cryogenic surface adsorption of hydrogen on porous host media (cryosorptive) at moderate pressures (50-70 bar).

Cryogenic storage in activated carbon can be done at 80 K (-193º C, or -316º F), a temperature higher than that required for liquid hydrogen storage (about -250º C). Hydrogen can sorb to surfaces in the activated carbon and can be released by increasing the temperature.

A number of researchers are investigating nanostructured forms of carbon storage of hydrogen storage. While structured forms of carbon offer advantages over non-structured activated carbon, the basic thermodynamic properties of carbon which determine the low operating temperatures at which hydrogen is desorbed from the medium remain the same.

Nanomix is proposing the use of a medium consisting of solid boron oxide and compounds closely related to it such as orthoboric acid, metaboric acid, hydrated boric acid, and disodium borohydrate. At pressures in the range of 1 bar, boron oxide media sorb hydrogen at about twice the level of carbon, when data are normalized to surface area, according to the patent document.

The heat of adsorption of hydrogen on the boron oxide medium is substantially higher than that of hydrogen on carbon. From this higher heat of absorption, it follows that at a given temperature within an operating temperature range of about 50 to about 200 K, and with results normalized to respective surface area, a boron oxide-based medium sorbs more hydrogen than a carbon-based medium. Expressed in another way, boron-oxide based media can be loaded with hydrogen and hold it at a temperature range significantly higher than that at which carbon-based media operates.

At a pressure of 20 bar, whereas temperature-driven desorption of hydrogen from carbon occurs over a range of about 50 K to about 150 K, temperature driven desorption from boron oxide and related compounds occurs over a range from about 100 K to about 200 K (-173º C to -73º C).

Nanomix also proposes a storage system that works with the storage medium for the storage and release of the gas.

At the outset of a fuel release, the cryosorptive hydrogen storage apparatus contains cold, pressurized hydrogen. Release of hydrogen from the storage apparatus is a process that consumes heat, thereby drawing down both the temperature and pressure. Heat can be provided to the cryosorptive storage apparatus by various direct approaches, or through the influx of warm, recycled hydrogen.

The hydrogen storage and release apparatus contains a recycle loop, which warms a portion of the effluxing hydrogen, and returns it to the storage apparatus, thereby maintaining pressure and temperature conditions that support continued hydrogen desorption from the storage medium.

We are pleased with our growing patent portfolio related to hydrogen storage technology. These advancements allow hydrogen to be stored at lower pressure than conventional methods, resulting in safe and effective energy systems. We are currently seeking industrial partners for the continued development of commercial and automotive hydrogen energy systems based on our patented technologies.

—David Macdonald, President and CEO of Nanomix

Resources:

• Operation of a hydrogen storage and supply system, US Patent #6,986,258

• Boron-oxide and related compounds for hydrogen storage, US Patent #6,991,773