Patent Application
20080090121
Several different metal hydrides have been extensively studied as potential solid-state storage media for hydrogen fuel systems. However, these materials thus far have proven to have only limited potential due to a relatively low gravimetric capacity for storage of recoverable hydrogen. For example, most hydrides are able to store up to about 2 weight percent of hydrogen, with certain high-potential materials, for example, sodium alanate (NaAlH4), potentially storing up to about 4 weight percent hydrogen at about 100° C. Even the high-potential materials fall short of the U.S. Department of Energy's stated goals of a hydrogen storage system that has a reversible storage capacity of 6 weight percent absorbed hydrogen and hydrogen release at less than 100° C. by 2010 and 9 weight percent by 2015. The DOE targets of 6 and 9 weight percent systems would require hydrides of at least 9 and 13.5 weight percent since at least a third of the weight goes to the balance of plant (the storage tank and heat exchange components). All the metal hydrides currently studied as hydrogen storage materials fall far short of these goals in terms of high weight percent capacity and low desorption temperatures. The most desired metal hydrides would be those with a gravimetric capacity greater than 9 weight percent and most preferably greater than 13.5 weight percent and a desorption temperature lower than 100° C. The desorption temperature is very critical and is thought to be dictated by the exhaust temperature of the PEM fuel cells and is widely thought to be less than 120° C. and more practically less than 100° C. Above 100° C., the superheated steam in the PEM fuel cells would likely significantly degrade the fuel cell life.
Embodiments of the present invention are based on a series of aluminoborane hydrides in the form of AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10. Examples of this series of aluminoborane hydrides include AlB4H11, AlB5H12, and AlB6H13 that were first synthesized by Francis L. Himpsl Jr. and Arthur C. Bond and published in the Journal of the American Chemical Society, volume 103, pages 1098-1102 in 1981. These aluminoborane hydrides have a hydrogen capacity of 13.5, 12.9 and 12.4 weight percent respectively. They are unique in their surprising high thermal stability: they are stable up to 100-140° C. which is significantly higher than the standard aluminum borohydride Al(BH4)3 (it can be written as AlB3H12). Al(BH4)3 has a melting point around −64.5° C. and a boiling point about 44.5° C. according to H. I. Schlesinger, R. T. Sanderson, and A. B. Burg in a paper published in Journal of the American Chemical Society, volume 62, pages 3421-3425 in 1940. Al(BH4)3 slowly decomposes even at ambient temperature. Al(BH4)3 is an extremely hazardous material since its vapor ignites spontaneously on exposure to air containing only traces of moisture. Therefore, Al(BH4)3 is unsuitable for hydrogen storage for on-board vehicular applications. It is contemplated by the present invention that aluminoborane hydrides AlB4H11, AlB5H12, and AlB6H13 are desirable as a hydrogen storage material due to the high weight percent capacity, good stability temperature and potential reversibility with a catalyst.
The aluminoborane hydrides AlB4H11, AlB5H12, and AlB6H13 usually exist in the form of amorphous materials with little distinctive x-ray diffraction peaks. Infrared (IR) spectra, however, reveal distinctive features for the identification of these materials. The aluminoborane hydride AlB4H11 exhibits the following principal absorption bands (in cm−1): 2530 (vs), 2458 (s), 2380 (s), 2350 (s), 2275 (vs), 2100 (m), 2050 (m), 1150 (m), 1050 (w), 990 (m), 935 (m), 910 (m), 850 (w), and 800 (w); where (vs), (s), (m), and (w) refer to very strong, strong, medium, and weak, respectively. The aluminoborane hydride AlB5H12 exhibits the following principal absorption bands (in cm−1): 2530 (s), 2460 (s), 2350 (m), 2270 (m), 2090 (m), 2030 (m), 1148 (m), 1040 (w), 990 (m), 900 (w), 850 (w), and 800 (w). The aluminoborane hydride AlB6H13 exhibits the following principal absorption bands (in cm−1): 2520 (s), 2450 (w), 2370 (m), 2355 (m), 2260 (s), 2100 (m), 1145 (m), 1040 (w), 970 (m), 925 (m), 910 (w), and 840 (w).
Other examples of this series of aluminoborane hydrides AlBxHn include AlB5H16, AlB7H20, and AlB9H24. They can be written as Al(BH4)2(B3H8), Al(BH4)(B3H8)2, and Al(B3H8)3. They have a hydrogen capacity of 16.5, 16.3, and 16.2 weight percent, respectively. These hydrides also have thermal stability significantly higher than standard aluminum borohydride Al(BH4)3. For instance, AlB9H24 is a non-volatile, colorless glass-like material. These aluminoborane hydrides are also contemplated as attractive as hydrogen storage materials by the present invention, especially in conjunction with a catalyst.
Accordingly, one embodiment of the present invention is a hydrogen storage material comprising an aluminoborane hydride AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10. Examples of aluminoborane hydride AlBxHn comprise AlB4H11, AlB5H12, AlB5H16, AlB6H13, AlB7H20, AlB9H24, and combinations thereof. These hydrides have good thermal stability and high weight percent hydrogen capacity to be desirable as hydrogen storage materials.
Another embodiment is a hydrogen storage material comprising an aluminoborane hydride AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10 and at least one catalyst. The catalyst is selected from hydrides, fluorides, chlorides, oxides, elements and alloys and combinations thereof. The hydride catalyst is selected from a group consisting of LiH, NaH, MgH2, KH, CaH2, LiAlH4, NaAlH4, Mg(AlH4)2, KAlH4, Ca(AlH4)2, TiH2, VH2, and combinations thereof. The catalyst of fluorides and chlorides are selected from the fluorides and chlorides of Li, Na, Mg, K, Ca, and transition metals. In one embodiment, the fluoride catalyst is selected from TiF3, FeF2, FeF3, CuF2, RuF3, RhF3 and ZrF4, and combinations thereof. In one embodiment, the chloride catalyst is selected from TiCl3, FeCl2, FeCl3, CuCl2, RuCl3, RhCl3, and ZrCl4, and combinations thereof. The oxide catalyst is selected from the group of Al2O3, SiO2, SnO, and transition metal oxides. In one embodiment, the oxide catalyst is Al2O3, SiO2, and Nb2O5 and combinations thereof. In another embodiment, the element and alloy catalyst is selected from carbon and transition metals and their alloys and borides. In another embodiment, the element and alloy catalyst is selected from the group consisting of Pd, Pt, Rh, Ru, La, Ni, carbon, Fe, Co, Cu, Ti, Re, LaNi5, FeTi, NiB, NiB2, and combinations thereof. Catalyst mixtures are highly desired to have the best kinetics in hydriding and dehydriding. For instance, TiCl3 and TiF3 are known to be effective catalysts for Al reaction with hydrogen and NaH. NaH, LiH and CaH2 are known to be effective in reducing the surface oxide of Al to make it more reactive. Other catalysts such as Rh on Al2O3, Pt on Al2O3, Rh on carbon, Pd on carbon, NiB, and NiB2 are conventionally used to improve the boron reactivity and transfer. Mixtures of these catalysts are contemplated to be effective in improving the kinetics of the hydriding and dehydriding reactions.
Yet another embodiment of the present invention is a hydrogen storage and delivery system 10 comprising a storage tank 12 and a hydrogen storage material 14; the hydrogen storage material 14 comprises an aluminoborane hydride AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10, as shown in
Yet another embodiment of the present invention is a fuel cell system 50 comprising a hydrogen storage system 52 for storing and releasing hydrogen, a fuel cell 54 in fluid communication with the hydrogen storage system 52 for receiving released hydrogen from the hydrogen storage system 52 and for electrochemically reacting the hydrogen with an oxidant 56 to produce electricity 58 and an anode exhaust 60, as shown in
Yet another embodiment of the present invention is a hydrogen-powered system 100 that comprises a hydrogen storage system 102 for storing and releasing hydrogen, an ICE engine or other hydrogen-consuming device 104 in fluid communication with the hydrogen storage system 102 for receiving released hydrogen from the hydrogen storage system 102, as shown in
In some embodiments, the aluminoborane hydride AlBxHn is decomposed or dehydrogenated to aluminum and boron and hydrogen is delivered to the hydrogen-consuming device 104 to generate energy. The process may produce a small amount of borane or diborane. In this case, it is an optional embodiment to pass the desorbed gas through a membrane or another medium (not shown) to remove the borane or diborane, thus providing high-purity hydrogen to the hydrogen-consuming device 104. This is particularly important to PEM fuel cells for which borane or diborane may be detrimental to PEM fuel cell performance.
One embodiment of the present invention is an apparatus for storing hydrogen 200, as shown in
In an exemplary, practical application of the hydrogen storage apparatus of the present invention, hydrogen is supplied from a source, such as a tank of hydrogen or a hydrogen production apparatus such as an electrolysis cell or hydrocarbon gas reformer, and then introduced into the storage component, where the storage medium is disposed within the storage component. In one example, the medium comprises a solid material, and in particular embodiments is a granular or powder material disposed within the storage component. Regardless of the form of the medium or where it is disposed, the hydrogen is exposed to the storage medium, whereupon the hydrogen reacts with the storage medium to form an aluminoborane hydride AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10. When hydrogen gas is required to be supplied, the storage medium is heated to decompose the hydride, and the resultant hydrogen gas is transported to an end use system or stored.
In addition to the addition of a hydrogen absorption/desorption catalyst to the aluminoborane hydride AlBxHn, to improve the kinetics, dopants may be contemplated to be added to the AlBxHn to replace Al to reduce the hydrogen desorption temperature and to improve the kinetics. Examples of such dopants include elements such as titanium, vanadium, chromium, zirconium, niobium, yttrium, lanthanum, manganese, nickel, iron, cobalt, silicon, copper, zinc and mixtures of any of the foregoing elements. The amount of dopants added into the AlBxHn depends in part upon the identity of the dopant and the composition of the AlBxHn. In certain embodiments the dopant is present in an amount of up to about 20 mole percent replacing aluminum (the 20 mole percent is based on aluminum content only), such as, for example, from about 0.5 mole percent to about 10 mole percent.
Embodiments of the present invention also include a method for storing and retrieving hydrogen. The method comprises providing a source of hydrogen; providing a storage component adapted to receive hydrogen from the source, the component comprising a hydrogen storage medium, wherein the hydrogen storage medium comprises boron and aluminum in a ratio equal to or greater than four and optionally at least one catalyst; and exposing the medium to hydrogen from the source. Upon exposure, the medium reacts with the hydrogen to form an aluminoborane hydride AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10, as described previously. Suitable alternatives for the source of hydrogen, the storage component, and the storage medium include those described above for the storage apparatus embodiments. The method, in some embodiments, further comprises heating the hydrogen storage medium to a hydrogen retrieval temperature, for example, typically greater than 100 C and often between 100 C and 500 C. Doing this will desorb hydrogen that is stored in the aluminoborane hydride AlBxHn, and, if the temperature is sufficiently high, will decompose the hydrides back to the original hydrogen storage medium material and hydrogen gas. The ability of the AlBxHn-bearing hydrogen storage medium to decompose to provide hydrogen potentially allows application of embodiments of the present invention in a number of useful areas, including, for example, on-board fuel storage for automobiles; fuel cells, including PEM fuel cells; and internal combustion engine powered automobiles.
Another embodiment of the present invention is the composition of matter that corresponds to certain aspects of the hydrogen storage medium described above. The material comprises an aluminoborane hydride AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10 and at least one catalyst. Particular embodiments of the material of the present invention include a material comprising an aluminoborane hydride AlBxHn wherein x is equal to or greater than 4 and n is equal to or greater than 10; up to about 10 mole percent of a hydrogen absorption/desorption catalyst, such as, for example, from about 0.1 mole percent to about 10 mole percent of the catalyst; up to about 20 mole percent of a dopant to replace aluminum, such as, for example, from about 0 mole percent to about 20 mole percent of the dopant.
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations, equivalents, or improvements therein may be made by those skilled in the art, and are still within the scope of the invention as defined in the appended claims.
