Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2000-05-05
2002-01-29
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C423S647000, C423S644000, C502S414000
Reexamination Certificate
active
06342198
ABSTRACT:
TECHNICAL FIELD
This invention relates to a hydrogen storage composition, methods for its manufacture and a method of providing a source of hydrogen.
BACKGROUND ART
Although metal hydrides offer a safe and convenient method for hydrogen storage, their practical application as hydrogen carriers still remains limited. This is caused by the fact that most applications require that metal hydrides exhibit in addition the following properties: high hydrogen capacity, fast kinetics of hydriding/dehydriding and suitable ranges of operational pressures and temperatures. Moreover, the hydrides should consist of inexpensive and available elements in order not to excessively raise the cost of hydrogen storage. Although the existing variety of metal hydrides offers a large spectrum of various properties which are suitable for hydrogen storage, so far none of the hydrides fulfills all the requirements. For example, FeTi or LaNi
5
can operate at room temperature at reasonable hydrogen pressures, but their low hydrogen capacity in practice excludes the use of these hydrides in transportation, or in portable hydrogen storage containers. V—Ti-based materials exhibit higher hydrogen capacities (up to 2 wt. %), but their cost is too high for any large-scale application.
Magnesium and magnesium-based alloys are the prime candidates for hydrogen storage amongst the existing metal hydrides. Magnesium forms a hydride (MgH
2
) which provides very high hydrogen capacity which at 7.6 wt. % is the highest of all metal hydrides with reversible performance. Additionally, the enthalpy of the hydride formation is large at 75 kJ/mole, which makes magnesium attractive for thermal energy storage. These features, combined with the very low cost and abundant accessibility of magnesium, suggest an excellent potential for hydrogen-related applications. However, to date magnesium hydride has been of no use for practical hydrogen storage because the reaction of hydriding/dehydriding is very slow and can be performed only at very high temperatures. In practice MgH
2
cannot be formed at ambient conditions, and high temperature and high hydrogen pressure are required for the reaction to occur. Moreover, the reaction of hydrogenation is usually blocked by surface oxidation of the material. In order to overcome this problem magnesium has to be activated prior to hydrogenation. Effective activation of magnesium as, for example, in [1] consists of several cycles of annealing at 400° C. in vacuum and in hydrogen, followed by annealing for several hours at 400° C. in vacuum. However, even after such activation, hydrogenation at a temperature of 350° C. and at a hydrogen pressure of 30 bars was not sufficient to initiate formation of magnesium hydride within 48 hours of annealing [1]. In practice, in order to achieve absorption rates for magnesium of the order of hours, the hydrogenation temperature should be higher than 400° C. at a hydrogen pressure of at least 30 bars [2, 3]. In addition, magnesium has a low equilibrium pressure of desorption and therefore desorption of hydrogen from magnesium hydride has to be performed also at very high temperatures, usually 350°-400° C.
An additional important feature of metal hydrides is that the reaction of dehydrogenation has an endothermic character. On one hand, this is very advantageous because it provides safety in the use of metal hydrides. In order to initiate desorption, the heat of the reaction has to be delivered to the system. Therefore desorption of hydrogen from the hydride can be performed with full control, avoiding excessive, uncontrollable production of free hydrogen. On the other hand, however, this feature poses important technical problems. In practice, the rate of hydrogen desorption can be significantly reduced by the very poor thermal conductivity of the hydride. In order to overcome this problem several technical solutions have been proposed, which in general involve improvement of heat transfer by designing special reaction beds [4, 5, 6].
Efficient metal hydride beds have various types of heat-transferring media incorporated into the bed. In practice, such media could be, for example, a heat sink in the form of rods, plates, wires or foams, made of a material with excellent thermal conductivity, for example, copper, aluminum or graphite. Such a heat sink, or a binder, or conductive matrix, can significantly increase the rate of the hydriding/dehydriding reaction. However, the resulting enhancement in the reaction kinetics is achieved always at the cost of the effective hydrogen capacity. The total weight of the reaction bed, including binders or heat sinks, increases substantially and the effective hydrogen capacity is in practice significantly reduced.
In response to the above drawbacks of metal hydrides, the present invention addresses simultaneously both problems: performance of metal hydride and heat-transfer limitations. As a result a viable metal hydride system is obtained, with high hydrogen capacity, fast performance and low cost.
DISCLOSURE OF THE INVENTION
It is an object of the invention to provide a hydrogen storage composition.
It is another object of the invention to provide a method of producing a source of hydrogen gas.
It is a further object of the invention to provide methods of producing the composition of the invention in the hydrogenated state.
In one aspect of the invention there is provided a hydrogen storage composition having a hydrogenated state and a dehydrogenated state, wherein (a) in said hydrogenated state said composition comprises (i) a metallic hydride having a metallic component which reversibly forms said hydride, and (ii) a metallic heat transfer medium in intimate contact with said hydride and effective to transfer heat to said hydride for dehydrogenation of said hydride, and (b) in said dehydrogenated state said composition comprises (iii) at least one intermetallic compound of said metallic component of said hydride and said metallic medium.
In particular, in the hydrogenated state, the hydride and the metallic medium are in fine particle form, preferably composed of particles having a size below 10 microns, more preferably below 100 nanometers, still more preferably below 50 nanometers and especially below 10 nanometers.
In another aspect of the invention there is provided a method of providing a source of hydrogen gas comprising liberating hydrogen from a composition of the invention as described above, at an elevated temperature, with transfer of heat to said hydride by said metallic heat transfer medium, removing said liberated hydrogen and regenerating said hydrogenated state by exposing said dehydrogenated state to hydrogen gas.
In other aspects there are provided methods for producing a composition of the invention.
In one embodiment of the latter aspect of the invention the method comprises mechanically alloying, rapidly solidifying or casting an intimate mixture of a metallic component which reversibly forms a metallic hydride and a metallic heat transfer medium, and hydriding said mixture with formation of the hydride of said metallic component while maintaining said metallic medium in non-hydrided form.
In another embodiment the method comprises mechanically alloying, rapidly solidifying or casting an intimate mixture of a metallic hydride having a metallic component which reversibly forms said hydride and a metallic heat transfer medium.
In still another embodiment the method comprises mechanically alloying, rapidly solidifying or casting an intermetallic compound of a metallic component which reversibly forms the metallic hydride and a metallic heat transfer medium and hydriding said intermetallic compound to form a hydride of said metallic component while maintaining said metallic medium in non-hydrided form.
DESCRIPTION OF PREFERRED EMBODIMENT
The essence of the invention is that a heat-transfer medium which forms a heat-conducting binder or matrix, is made an integral part of the metal hydride system and plays a crucial role as a reagent in the hydrogenation/dehy
Ström-Olsen John Olaf
Zaluska Alicja
Zaluski Leszek
Griffin Steven P.
Ildebrando Christina
McGill University
Renault Swabey Ogilvy
LandOfFree
Hydrogen storage composition 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 composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrogen storage composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2830342