Chemistry of inorganic compounds – With additive – Additive contains metal – boron – or silicon
Reexamination Certificate
1999-06-18
2001-09-25
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
With additive
Additive contains metal, boron, or silicon
C423S448000, C423S460000
Reexamination Certificate
active
06294142
ABSTRACT:
TECHNICAL FIELD
This invention pertains to graphite or carbon and alkali metal compositions for the reversible storage of hydrogen gas and to methods for making such compositions.
BACKGROUND OF THE INVENTION
Hydrogen is a very energetic, clean burning fuel. It can be burned with great energy release in air or oxygen-enriched atmosphere to yield water without unburned hydrocarbons or carbon oxides as byproducts. The problem, of course, is that it is difficult to store hydrogen for mobile applications such as automobiles or trucks. Hydrogen can be stored as a liquid only if it can be kept very cold and under high pressure. If hydrogen is to be stored as a gas, most previous approaches have been to use metal containers suitable for confining the gas under very high pressures. There are no practical materials that can reversibly absorb or adsorb appreciable amounts of hydrogen at low pressure and give it up as a gas on demand. Accordingly, hydrogen has not been available as a practical fuel in vehicular applications.
There is a need to advance the art of hydrogen storage materials that can take up and temporarily hold substantial quantities of hydrogen at relatively low pressure and give up gaseous hydrogen on demand.
SUMMARY OF THE INVENTION
This invention provides a fully reacted alkali metal intercalated graphite or non-graphitic carbon that is capable of reversibly absorbing unusually large amounts of hydrogen gas. It is preferred to use graphite. One use of such material is as a temporary storage device for hydrogen fuel in connection with engines and fuel cells. Another use for the material is as a separation device to remove hydrogen from a mixture of gases.
One aspect of the invention is a method of forming a fully reacted alkali metal-graphite combination that has substantial hydrogen-adsorbing capabilities. The method suitably utilizes ordinary graphite or non-graphitic carbon and one or more alkali metals selected from the group consisting of lithium, sodium and potassium. Graphite, of course, is a crystalline form of carbon in which the carbon atoms lie in planes in C
6
hexagonal cells.
In accordance with the method, a mixture of six to 24 atomic parts of carbon (graphite) and one atomic part of alkali metal is formed. Due to the presence of the readily oxidized metal, the mixture is prepared under a substantially non-oxidizing atmosphere, suitably an argon atmosphere. The dry solid mixture is then vigorously compacted, for example in a die or mold, and heated to promote substantially complete intercalation of the alkali metal atoms between the graphene planes. When lithium is the alkali metal, it is preferred that the reactants be mixed in proportions of six to twelve atoms of carbon per atom of lithium. For sodium, the preferred ratio is eight to twelve carbon atoms per sodium atom, and for potassium the atomic ratio is eight to 24 carbon atoms. When mixtures of metals are used, the ratios are modified in proportion to the amounts of the respective metals.
In these proportions and under suitable conditions of pressure and temperature, the starting materials are fully altered to a binary intercalated structure. For example, an x-ray diffraction analysis of the product will normally contain none of the diffraction peaks of graphite or the alkali metal but will display a diffraction pattern characteristic of an alkali metal intercalated carbon composite suitable for the practice of this invention.
In a preferred embodiment of the invention, the graphite or non-graphitic carbon is pre-reacted with a small (less than specified amount) of the intended alkali metal. A precursor material is made using, for example, about 30 atomic parts of graphite per part of alkali metal. The precursor is suitably made using the same reaction conditions as for the final intercalated product. The formation of the precursor seems to initially exfoliate the graphite planes to better prepare the precursor for further intercalation with the alkali metal to achieve the specified composition for hydrogen storage.
The fully-reacted molded composite is usually initially in the form of a molded body. It can be used in the form of a molded body or comminuted to particles of a desired size. But a first surprising characteristic of the material is its capacity to take up hydrogen gas.
When a quantity of potassium-intercalated graphite is placed in a closed container with hydrogen gas at, e.g., 10 pounds per square inch gage (psig) and 150° C., the pressure in the vessel drops. If the amount of hydrogen is not sufficient to saturate the metal-graphite composite, the pressure falls below atmospheric pressure. The weight of the material increases, for example, by more than one-tenth to one-third of its original weight. The hydrogen absorption of the material is largely reversible.
Upon heating, a material with stored hydrogen releases hydrogen gas. Indeed, hydrogen intake or release can be cyclically induced by temperature or pressure change. In general, by decreasing the temperature or increasing hydrogen partial pressure, hydrogen absorption is increased. Conversely, by increasing temperature or decreasing hydrogen pressure, the hydrogen loading of the metal-graphite composite is decreased.
Obviously, the alkali metal-intercalated graphite material of this invention can be used to temporarily store hydrogen fuel for engines, fuel cells and the like. It can also be used in other hydrogen storage applications or in hydrogen separation applications.
There is an additional surprising feature of the binary material produced in accordance with this invention. It is found that when the lithium, sodium and/or potassium intercalated graphite of this invention is loaded with hydrogen, the resultant ternary material (of metal, graphite and hydrogen origin) has very interesting magnetic and electrical conductivity properties. By varying the hydrogen content of the ternary material, one “tunes” the electrical conductivity and magnetic properties as the material functions within the metal-insulator electron energy gap.
It is believed, without intending to limit the invention in any way, that the unexpected hydrogen storage capacity is related to nature of the electrons in the binary structure and resulting metal-graphite hydrogen ternary. The electrons are of mobile &pgr; character in the binary. As the hydrogen is absorbed, its valence electron partially escapes into the &pgr; electron environment. The effective volume of the hydrogen is decreased and the capacity of the binary composite for hydrogen is increased. Further, the combination of the hydrogen valence electrons with the &pgr; electrons of the binary contribute to the new electronic and magnetic properties of the metal-graphite-hydrogen ternary.
Other objects and advantages of this invention will become more apparent from a detailed description of preferred embodiments which follows. Reference will be had to the drawings that are described in the following section.
REFERENCES:
patent: 3278632 (1966-10-01), Wambling et al.
patent: 4580404 (1986-04-01), Pez et al.
patent: 5653951 (1997-08-01), Rodriguez et al.
patent: 5698140 (1997-12-01), Lamb et al.
Chen et al, “High H2Uptake by Alkali-Doped Carbon Nanotubes under Ambient Pressure and Moderate Temperatures”,Science, vol. 285, Jul. 2, 1999, pp. 91-93.
Brooks Cary W.
General Motors Corporation
Grove George A.
Hendrickson Stuart L.
LandOfFree
Hydrogen storage systems and method of making them does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydrogen storage systems and method of making them, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrogen storage systems and method of making them will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2524809