KR20060123300A - Catalyzed hydrogen desorption in mg-based hydrogen storage material and methods for production thereof - Google Patents

Abstract

A magnesium-based hydrogen storage material including magnesium or a magnesium-based hydrogen storage alloy and a hydrogen desorption catalyst which is insoluble in said magnesium- based hydrogen storage alloy and is in the form of: 1) discrete dispersed regions of catalytic material in the bulk of said magnesium or magnesium- based hydrogen storage alloy; 2) discrete dispersed regions on the surface of particles of said magnesium or magnesium-based hydrogen storage alloy; 3) a continuous or semi-continuous layer of catalytic material on the surface of said magnesium or magnesium-based hydrogen storage alloy which is in bulk or particulate form; or 4) combinations thereof. Methods of producing the material are also disclosed.

Description

Catalytic hydrogen desorption in Mg-based hydrogen storage material and methods for production

The present invention generally relates to a hydrogen storage material, more particularly to a magnesium-based hydrogen storage material, wherein the hydrogen desorption is catalyzed by a material insoluble in the magnesium-based hydrogen storage material. The insoluble catalyst material may be in the form of: 1) discontinuous dispersed regions of the catalyst material in the hydrogen storage material bulk; 2) discrete discrete regions on the particle surface of the hydrogen storage material; 3) a continuous or semicontinuous layer of catalytic material on the surface of the bulk or particulate hydrogen storage material; Or 4) combinations thereof.

Increasing energy needs should be made aware of the fact that traditional energy resources such as coal, oil, or natural gas are not inexhaustible, or at least that they are always more expensive, and that it is justified to consider replacing them with hydrogen. Experts are urged.

Hydrogen can be used, for example, as a fuel for internal combustion engines instead of hydrocarbons. In this case, it has the advantage of eliminating air pollution resulting from the formation of carbon, nitrogen and sulfur upon combustion of hydrocarbons. Hydrogen can also be used to fuel hydrogen-air fuel cells for the production of electricity needed for electric motors.

One of the problems caused by the use of hydrogen is its storage and transportation. A number of solutions have been proposed:

Hydrogen can be stored in steel cylinders under high pressure, but this method has the disadvantage of requiring dangerous and heavy containers that are difficult to handle (other than having a low storage capacity of about 1% by weight). Hydrogen can also be stored in cryogenic containers, but this leads to drawbacks associated with the use of cryogenic liquids such as, for example, the high cost of the container. The container also requires careful handling. There is also a "boil off" loss of about 2-5% per day here.

Another way to store hydrogen is to store it in hydroxide form. The hydroxide is then decomposed at the appropriate time to supply hydrogen. Hydroxides of iron-titanium, lanthanum-nickel, vanadium, and magnesium have been used in this way, as described in French Patent No. 1,529,371.

Since the initial discovery that hydrogen can be stored in the form of safe and convenient solid metal hydroxides, researchers have been trying to produce hydrogen storage materials with optimal properties. In general, the ideal material properties these researchers have attempted to achieve include: 1) high hydrogen storage capacity; 2) lightweight materials; 3) suitable hydrogen absorption / desorption temperature; 4) moderate absorption / desorption pressure; 5) fast absorption kinetics; And 6) long absorption / desorption cycle life. In addition to these material properties, ideal materials are inexpensive and easy to manufacture.

The MgH ₂ -Mg system is the most suitable of all known metal-hydroxide and metal systems that can be used as reversible hydrogen-storage systems, because it has a maximum weight percent (7.65 weight percent) of theoretical hydrogen storage capacity, Therefore, it has the maximum theoretical energy density per unit weight of the storage material (2332 Wh / kg; Reilly & Sandrock, Spektrum der Wissenschaft, Apr. 1980, 53).

Although this property and the relatively low price of magnesium seem to make MgH ₂ -Mg an optimal hydrogen storage system for transport, ie for hydrogen powered vehicles, its unsatisfactory dynamics have prevented it from being used to date. It is known by way of example that pure magnesium can only be hydrided under vigorous conditions, perhaps only at a temperature of 400 ° C., and then only very slowly and incompletely. The resulting dehydriding rate of the hydroxides is also unacceptable as hydrogen storage materials (Genossar & Rudman, Z. f. Phys. Chem., Neue Folge 116,215 [1979], and references cited therein). ).

Moreover, the hydrogen storage capacity of the magnesium reservoir decreases during the charge / discharge cycle. This phenomenon can be explained by the progressive poisoning of the surface that renders the magnesium atoms located inside the reservoir inaccessible to hydrogen during charging.

To release hydrogen in a conventional magnesium or magnesium / nickel storage system, temperatures of 250 ° C. or higher are required simultaneously with a large amount of energy supply. High temperature levels and high energy requirements for releasing hydrogen have the effect that, for example, an automobile with an internal combustion engine cannot be operated exclusively from such alloys. This occurs because the energy contained in the exhaust gas is sufficient to meet only 50% of the hydrogen demand of the internal combustion engine from the magnesium or magnesium / nickel alloy in the most preferred case (maximum charge amount). Thus, the remaining hydrogen demand must be obtained from another hydroxide alloy. For example, this alloy can be titanium / iron hydroxide (typically a low temperature hydroxide vessel) that can be operated at temperatures below 0 ° C. Such low temperature hydroxide alloys have the disadvantage of having low hydrogen storage capacity.

Storage materials have been developed in the past, and the storage materials have a relatively high storage capacity, but hydrogen is nevertheless released at temperatures below about 250 ° C. US 4,160,014 discloses a hydrogen storage material of formula Ti _[1-x] Zr _[x] Mn _[2-yz] Cr _[y] V _[z] . Wherein x is 0.05 to 0.4, y is 0 to 1, and z is 0 to 0.4. Up to about 2% by weight of hydrogen may be stored in such alloys. In addition to this relatively low storage capacity, such alloys also have the disadvantage that the price of the alloy is very high when metal vanadium is used.

Moreover, U. S. Patent No. 4,111, 689 discloses a storage alloy comprising 31 to 46 weight percent titanium, 5 to 33 weight percent vanadium, and 36 to 53 weight percent iron and / or manganese. Although alloys of this type have a larger storage capacity for hydrogen than alloys according to US Pat. No. 4,160,014, incorporated herein by reference, they have the disadvantage that a temperature of at least 250 ° C. is necessary to fully release hydrogen. . At temperatures up to about 100 ° C., about 80% of the hydrogen content can be released in the best case. However, high discharge capacity, especially at low temperatures, is often required in the industry because the heat required to release hydrogen from the hydroxide vessel is often only available at low temperature levels.

In contrast to other metals or metal alloys, in particular metal alloys containing titanium or lanthanum, magnesium is more suitable for the storage of hydrogen because of its low specific gravity as a storage material, in addition to its low material cost. However, the hydriding is

Mg + H ₂ → MgH ₂

In general, it is more difficult to achieve with magnesium because the surface of magnesium will oxidize rapidly in air to form a stable MgO and / or Mg (OH) ₂ surface layer. These layers resist the dissociation of hydrogen molecules in addition to the absorption of the resulting hydrogen atoms into the magnesium storage mass and their diffusion from the grain shaped particle surface.

Various foreign metals (German Offenlegungsschriften 2 846 672 and 2 846 673), or Mg ₂ Ni or Mg ₂ Cu (Wiswall, Top Appl. Phys. 29, 201 [1978] and Genossar & Rudman op. Cit.) And aluminum (Douglass, Metall. Trans. 6a, 2179 [1975]), with intermetallic compounds such as LaNi ₅ (Tanguy et al., Mater. Res. Bull. 11, 1441 [1976]), Doping magnesium with individual dissimilar metals such as indium (Mintz, Gavra, & Hadari, J. Inorg. Nucl. Chem. 40, 765 [1978]), or iron (Welter & Rudman Scripta Metallurgica 16, 285 [1982]) Intensive efforts have been made in recent years to improve the hydriding ability of magnesium by forming or alloying it.

Although these attempts have somewhat improved the dynamics, certain inherent shortcomings have not yet been eliminated from the resulting system. Preliminary hydriding of magnesium doped with bimetallic or intermetallic compounds still requires vigorous reaction conditions, system kinetics will be satisfactory and the reversible hydrogen content will only be high after many cycles of hydriding and dehydrating. Will be. A significant proportion of bimetallic or expensive intermetallic compounds is also needed to improve the kinetics. Moreover, the storage capacity of such systems is generally far below what is theoretically expected for MgH ₂ .

The storage quality of magnesium and magnesium alloys can also be improved by the addition of materials that can help to decompose stable oxides of magnesium. For example, such an alloy is Mg ₂ Ni, in which Ni appears to form an unstable oxide. In this alloy, thermodynamic examination indicated that the surface reaction, Mg ₂ Ni + 0 ₂ → 2MgO + Ni, expanded to nickel metal inclusions that catalyze the hydrogen decomposition-absorption reaction. References can be made to A. Seiler et al., Journal of Less-Common Metals 73,1980, 193 pages or less.

One possibility for the catalysis of the hydrogen decomposition-absorption reaction on the surface of magnesium also lies in the formation of a two-phase alloy. In the biphasic alloy, one phase is a hydroxide former and the other is a catalyst. Thus, as mentioned below in F. G. Eisenberg et al. Journal of Less-Common Metals 74,1980, 323, it is known to use galvanic electrically nickelated magnesium for hydrogen storage. However, there have been problems encountered during the deposition and distribution of nickel on the magnesium surface.

As mentioned below in the Zeitschrift fur Physikalische Chemie Neue Folge, J. Genossar et al. It is also known that a eutectic mixture of magnesium can be used as the hydroxide-forming phase with magnesium copper (Mg ₂ Cu). The storage capacity per volume of material achieved through these magnesium-containing particulates, however, does not meet any high demand due to the amount of magnesium copper required for the process mixture.

Scientists of this age have observed a variety of materials and have assumed that certain crystal structures are required for hydrogen storage. See, eg, "Hydrogen Storage in Metal Hydride", Scientific American, Vol. 242, No. 2, pp. See 118-129, February, 1980. It has been found that it is possible to remedy many of the shortcomings of the prior art materials using other kinds of materials, namely disordered hydrogen storage materials. For example, US Pat. No. 4,265,720 to Guenter Winstel for "Storage Materials for Hydrogen" describes hydrogen storage of amorphous or microcrystalline silicon. The silicon is preferably a thin film combined with a suitable catalyst and on a substrate.

Japanese Patent Laid-Open Publication No. 55-167401 to Matsumato et al. Discloses bi- or tri-element hydrogen storage materials of at least 50% by volume amorphous structure. The first element is selected from Ca, Mg, Ti, Zr, Hf, V, Nb, Ta, Y, and lanthanide groups, and the second element is Al, Cr, Fe, Co, Ni, Cu, Mn, and Si Selected from the group. The third element is selected from the group B, C, P, and Ge may optionally be present.

According to the teaching of Japanese Patent Laid-Open No. 55-167401, an amorphous structure is necessary to overcome the problem of undesirably high desorption temperature characteristics of most crystalline systems. High desorption temperatures (eg above 150 ° C.) severely limit the use in which the system can be placed.

According to Matsumoto et al., Materials of at least 50% amorphous structure can desorb at least some hydrogen at relatively low temperatures, because the binding energy of individual atoms is not uniform as in the case of crystalline materials, but is distributed over a wide range. to be.

Matsumoto et al. Claim materials of at least 50% amorphous structure. Although Matsumoto et al. Do not provide any further teaching as to the meaning of the term “amorphous,” the scientifically accepted definition of the term includes a maximum short range order of about 20 ms or less.

The use of amorphous structural materials by Matsumoto et al. To obtain better desorption kinetics due to non-flat hysteresis curves is an inadequate and partial solution. Other problems found in crystalline hydrogen storage materials, particularly low useful hydrogen storage capacity, remain at moderate temperatures.

However, even better hydrogen storage results, i.e., long cycle life, good physical strength, low absorption / desorption temperature and pressure, reversibility, and resistance to chemical poisoning are sufficient to modify the disordered metastable hydrogen storage material. If the benefits are obtained, they can be realized. A disorderly structurally metastable hydrogen storage material is described in US Pat. No. 4,431,561 to Stanford R. Ovshinsky et al., For "Hydrogen Storage Materials and Method of Making the Same." As described herein, disordered hydrogen storage materials characterized by chemically modified and thermodynamically metastable structures can be tailored to possess all of the hydrogen storage properties desirable for a wide range of commercial uses. The modified hydrogen storage material can be made to have a larger hydrogen storage capacity than the host materials of single phase crystals. The bond strength between hydrogen and storage sites in such modified materials can be adjusted to provide a spectrum of binding possibilities. Disordered hydrogen storage materials that are chemically modified and thermodynamically metastable structures also have significantly increased densities of catalytically active sites for improved hydrogen storage kinetics and increased resistance to poisons. .

The interdependent coupling of selected reformers included in the selected host matrix provides the degree and quality of structural and chemical modifications, which modify chemical structures and forms, physical structures and forms, and Stabilizes electronic structure and morphology.

The backbone of the modified hydrogen storage material is a lightweight master matrix. The host matrix is structurally modified with a selected reformer to provide a disordered material with a local chemical environment that results in the desired hydrogen storage properties.

Another advantage of the host matrix described by Ovshinsky et al. Is that it can be modified in a substantially continuous area that changes the proportion of the reformer element. This capability allows the host matrix to be treated with a custom or engineered hydrogen storage material having properties suitable for a particular use by the reformer. This is in contrast to the host crystalline materials of the multicomponent single phase which generally have a very limited range of available stoichiometry. Thus, control of a continuous range of thermodynamic and kinematic, chemical and structural modifications of such crystalline materials is not possible.

A further advantage of these disordered hydrogen storage materials is that they are much more resistant to poisons. As mentioned above, these materials have a much higher density of catalytically active sites. Thus, a certain number of such sites can be sacrificed for the effects of poisonous species, while many non-addicted active sites still remain to provide the desired hydrogen storage kinetics.

Another advantage of these disordered materials is that they can be designed to be more mechanically flexible than single phase crystalline materials. The disordered material may thus be more distorted during expansion and contraction, allowing for greater mechanical stability during absorption and desorption cycles.

One disadvantage of this disordered material is that in the past, some of the Mg-based alloys were difficult to produce. In particular, these materials did not form a solution in the melt. In addition, the most promising materials (ie magnesium-based materials) are very difficult to make in bulk form. That is, thin film sputtering techniques can produce small amounts of such disordered alloys, but there is no bulk manufacturing technique.

Then in the mid-1980s, two groups developed mechanical alloying techniques to produce bulky disordered magnesium alloy hydrogen storage materials. Mechanical alloys have been found to promote alloying of elements with widely different vapor pressures and melting points (such as Mg and Fe, or Ti), especially when there are no stable intermetallic phases. Conventional techniques such as induction melting have been found to be inadequate for this purpose.

The first of the two groups was a team of French scientists who investigated the mechanical alloying of Mg-Ni system materials and their hydrogen storage properties. Senegas et al., "Phase Characterization and Hydrogen Diffusion Study in the Mg-Ni-H System", Journal of the Less-Common Metals, Vol. 129,1987, pp. 317-326 (binary mechanical alloys of Mg and Ni incorporating 0, 10, 25 and 55 wt.% Ni); and also Song et al., "Hydriding and Dehydriding Characteristics of Mechanically Alloyed Mixtures Mg-x wt.% Ni (x = 5, 10, 25 and 55) ", Journal of the Less-Common Metals, Vol. 131, 1987, pp. 71-79 (binary mechanical alloys of Mg and Ni incorporating 5, 10, 25 and 55 wt.% Ni).

The second of the two groups was a team of Russian scientists investigating the hydrogen storage properties of binary mechanical alloys of magnesium and other metals. Ivanov et al., "Mechanical Alloys of Magnesium--New Materials For Hydrogen Energy", Doklady Physical Chemistry (English Translation) vol. 286: 1-3,1986, pp. 55-57, (binary mechanical alloys of Mg with Ni, Ce, Nb, Ti, Fe, Co, Si and C); See also Ivanov et al., "Magnesium Mechanical Alloys for Hydrogen Storage", Journal of the Less-Common Metals, vol. 131,1987, pp. 25-29 (binary mechanical alloys of Mg with Ni, Fe, Co, Nb and Ti); And Stepanov et al., "Hydriding Properties of Mechanical Alloys of Mg-Ni", Journal of the Less-Common Metals, vol. 131,1987, pp. See 89-97 (binary mechanical alloys of the Mg-Ni system). In addition, Konstanchuk et al., "The Hydriding Properties of a Mechanical Alloy With Composition Mg-25% Fe", a joint study of the French and Russian groups, Journal of the Less-Common Metals, vol. 131, 1987, pp. See 181-189 (binary mechanical alloy of Mg and 25 wt.% Fe).

Later, in the late 1980s and early 1990s, a group of Bulgarian scientists (sometimes in collaboration with a group of Russian scientists) examined the hydrogen storage properties of mechanical alloys of magnesium and metal oxides. "Hydriding Kinetics of Mixtures Containing Some 3d-Transition Metal Oxides and Magnesium" by Khrussanova et al., Zeitschrift fur Physikalische Chemie Neue Folge, Munchen, vol. 164, 1989, pp. 1261-1266 (comparing binary mixtures and mechanical alloys of Mg with TiO ₂ , V ₂ 0 ₅ , and Cr ₂ 0 ₃ ); And "Surface Composition of Mg--TiO ₂ Mixtures for Hydrogen Storage, Prepared by Different Methods" by Peshev et al., Materials Research Bulletin, vol. 24, 1989, pp. See 207-212 (comparing conventional mixtures and mechanical alloys of Mg and TiO ₂ ). See also Khrussanova et al., "On the Hydriding of a Mechanically Alloyed Mg (90%)-V ₂ 0 ₅ (10%) Mixture", International Journal of Hydrogen Energy, vol. 15, No. 11, 1990, pp. 799-805 (investigating the hydrogen storage properties of a binary mechanical alloy of Mg and V ₂ O ₅ ); And "Hydriding of Mechanically Alloyed Mixtures of Magnesium With MnO ₂ , Fe ₂ 0 ₃ , and NiO", Materials Research Bulletin, vol. 26, 1991, pp. 561-567 (investigating the hydrogen storage properties of a binary mechanical alloys of Mg with and MnO ₂ , Fe ₂ 0 ₃ , and NiO). Finally, Khrussanova et al., "The Effect of the d-Electron Concentration on the Absorption Capacity of Some Systems for Hydrogen Storage", Materials Research Bulletin, vol. 26, 1991, pp. 1291-1298 (investigating d-electron concentration effects on the hydrogen storage properties of materials, including mechanical alloys of Mg and 3-d metal oxides); And Mitov et al. "A Mossbauer Study of a Hydrided Mechanically Alloyed Mixture of Magnesium and Iron (III) Oxide", Materials Research Bulletin, vol. 27, 1992, pp.905-910 (Investigating the hydrogen storage properties of a binary mechanical alloy of Mg and Fe ₂ 0 ₃ ).

More recently, a group of Chinese scientists investigated the hydrogen storage properties of several mechanical alloys of Mg with other metals. Yang et al., "The Thermal Stability of Amorphous Hydride Mg ₅₀ Ni ₅₀ H ₅₄ and Mg ₃₀ Ni ₇₀ H ₄₅ ", Zeitschrift fur Physikalische Chemie, Munchen, vol. 183,1994, pp. 141-147 (Investigating the hydrogen storage properties of the mechanical alloys Mg ₅₀ Ni ₅₀ and Mg ₃₀ Ni ₇₀ ); And "Electrochemical Behavior of Some Mechanically Alloyed Mg-Ni-based Amorphous Hydrogen Storage Alloys" by Lei et al., Zeitschrift fur Physikalische Chemie, Munchen, vol. 183,1994, pp. See 379-384 (investigating the electrochemical [i, e. Ni-MH battery] properties of some mechanical alloys of Mg--Ni with Co, Si, Al, and Co-Si).

A short-range, or local order, is described in detail in Ovshinsky, U.S. Patent No. 4,520,039, entitled "Compositionally Varied Materials and Method for Synthesizing the Materials," the contents of which are incorporated by reference. Included. This patent does not require any periodic local alignment of disordered materials, and spatial and orientational arrangements of similar or dissimilar atoms or groups of atoms are those of a local arrangement in which it is possible to qualitatively create new phenomena. We also disclosed how this is possible with increased accuracy and control. Moreover, this patent need not be limited to the valence "d-band" or "f-band" atoms used, but a controlled aspect of the interaction with the local environment and / or orbital overlap affects the properties and thus the function of the material. It can be any atom that plays an important role physically, electronically, or chemically. The elements of these materials offer various bonding possibilities due to the d-orbitals. The "porcupine effect" of the d-orbital provides a tremendous increase in density and thus in active storage sites. This technology results in a means of synthesizing disordered new materials from several different points of view at the same time.

Ovshinsky has previously shown that the number of surface sites can be significantly increased by making an amorphous film, the bulk of which resembles the surface of the desired relatively pure material. Ovshinsky also used complex elements to provide additional binding and local environmental alignment that allows the material to obtain the required electrochemical properties. As Ovshinsky described in "Principles and Applications of Amorphicity, Structural Change, and Optical Information Encoding, 42 Journal De Physique at C4-1096 (October 1981)":

Amorphicity is a general term that refers to the lack of evidence of X-ray diffraction of long range periodicity and is not a sufficient description of the material. There are several important factors to consider in order to understand amorphous materials: the form of chemical bonds, the number of bonds produced by local alignment, that is, their coordination, and the chemical and geometrical implications of the various configurations resulting. Impact of the entire local environment. Amorphousness is not determined by any packing of atoms that appear to be hard spheres, and an amorphous solid is not simply a master with randomly imbedded atoms. Amorphous materials should appear to consist of interacting matrices. The electronic arrangement of the mattress is generated by free energy forces and they can in particular be defined by the chemical nature and coordination of the constituent atoms. Using complex orbital elements and a variety of manufacturing techniques, it is possible to outwit normal relaxation that reflects equilibrium conditions, and because of the three-dimensional freedom of the amorphous state, a whole new form of amorphous Substances--Make chemically modified substances ...

If amorphousness is to be understood as a means of introducing surface sites into a membrane, a "disorder" that takes into account the full spectrum of effects such as porosity, topology, crystallites, properties of the sites, and distances between the sites It is possible to produce. Thus, rather than studying material changes that produce aligned materials with the maximum number of surface bonds and surface irregularities that occur by chance, Ovshinsky and his team at ECD began to create "disordered" materials with the desired irregularities just made. See US Pat. No. 4,623,597. The disclosure of this patent is incorporated by reference.

The term "disordered" as used herein to refer to an electrochemical electrode material corresponds to the meaning of the term as used in the following literature:

Disordered semiconductors can exist in several structural states. This structural factor constitutes a new variable in which the physical properties of the substance can be controlled. Moreover, structural disorders open up the possibility of producing new compositions and mixtures in metastable states that far exceed the limits of thermodynamic equilibrium. Therefore, we note the following as more distinctive features. In many disordered materials, it is possible to adjust the short-range order parameter, including forcing new coordination numbers on elements, resulting in drastic changes in the properties of these materials. It is possible to get change ...

S. R. Ovshinsky, The Shape of Disorder, 32 Journal of Non-Crystalline Solids at 22 (1979) (emphasis added).

The "short-range order" of such disordered materials is described in The Chemical Basis of Amorphicity: Structure and Function, 26: 8-9 Rev. Roum. Phys. at 893-903 (1981): is further explained by Ovshinsky in:

[End] -range alignment is not preserved. In fact, when the symmetry of the crystal is broken, it becomes impossible to maintain the same short-range alignment. The reason for this is that the short range alignment is regulated by the force region of the electron orbital and therefore the environment must be fundamentally different in the corresponding crystalline and amorphous solids. In other words, what determines the electrical, chemical, and physical properties of a material is the interaction of local chemical bonds with the surrounding environment, and this interaction can never be the same as in crystalline materials in amorphous materials. The orbital relationships that can exist in three-dimensional space in non-material materials are the basis for new geometry, many of which are inherently anti-crystalline in nature. Distortion of bonds and substitution of atoms can be a good reason for causing amorphousness in single element materials. However, in order to fully understand amorphousness, one must understand the essential three-dimensional relationship in the amorphous state, because they generate an internal topology that is incompatible with the translational symmetry of the crystal lattice. What is important in the amorphous state is the fact that it can make the infinity of a material without any counterpart, and even a material with a crystalline analog is mainly similar in chemical composition. The spatial and energetic relationship of these atoms can be entirely different in their amorphous and crystalline form even though their chemical elements are identical.

Based on the principles of such disordered materials described above, three highly efficient electrochemical hydrogen storage negative electrode materials have been devised. These three negative electrode materials, individually and collectively, will be referred to hereinafter as "Ovonic". One of these species is a La-Ni ₅ -type negative electrode material, which is a disordered multicomponent alloy through the addition of rare earth elements such as Ce, Pr, and Nd, and other metals such as Mn, Al, and Co, It has recently been modified to become "Ovonic". The second of these species is the Ti-Ni-type negative electrode material, which was introduced and developed by the assignee of the subject invention and through the addition of transition metals such as Zr and V and other metal modifier elements such as Mn, Cr, Al, Fe, etc. It has been modified to be an disordered multielement alloy, or "Ovonic." The third of these species is described in U.S. Patent Nos. 5,506,069; 5,616,432; And the disordered multicomponent MgNi-type negative electrode material described in US Pat. No. 5,554,456 (the disclosure of which is incorporated herein by reference).

Based on the principle expressed in Ovshinsky's '597 patent, an Ovonic Ti-V-Zr-Ni type active material is disclosed in U.S. Patent No. 4,551,400 ("' 400 patent") to Sapru, Fetcenko, and the like. Is included for reference. This second species of Ovonic substance reversibly forms hydroxides to store hydrogen. All materials used in the '400 patent utilize a Ti-V-Ni composition, where at least Ti, V, and Ni are present with at least one Cr, Zr, and Al. The materials of the '400 patent are generally polyphase polycrystalline materials, which include, but are not limited to, phases of one or more Ti-V-Zr-Ni materials with crystal structures of C ₁₄ and C ₁₅ forms. Another commonly assigned U.S. Pat.No. 4,728,586 ("'586 patent"), named Ovonic Ti-V-Zr-Ni alloys, is Enhanced Charge Retention Electrochemical Hydrogen Storage Alloys and an Enhanced Charge Retention Electrochemical Cell. And its disclosure is incorporated by reference.

Characteristic surface roughness of the metal electrolyte interface is a result of the disordered nature of the material as disclosed in generally assigned US Pat. No. 4,716,088 to Reichman, Venkatesan, Fetcenko, Jeffries, Stahl, and Bennet. The disclosure of this patent is incorporated by reference.

In addition to many alloys and their phases, because all the constituent elements are present throughout the metal, they also appear in cracks that form on the surface and metal / electrolyte interface. Thus, characteristic surface roughness describes the interaction of the alloy and the physical and chemical properties of the master metal in addition to the crystallographic phases of the alloy in an alkaline environment. The fine chemical, physical, and crystallographic parameters of each phase in the hydrogen storage alloy material are important in determining its macroscopic electrochemical properties.

In addition to the physical properties of the rough surface, it was observed that the V-Ti-Zr-Ni type alloys tend to reach steady state surface conditions and particle sizes. This steady state surface condition is characterized by a relatively high concentration of metallic nickel. This observation is consistent with the relatively high removal rates of titanium and zirconium oxides from the surface through precipitation, and much lower nickel dissolution rates. The resulting surface has a higher nickel concentration than would be expected from the bulk composition of the negative hydrogen storage electrode. Nickel in the metallic state is electrically conductive and catalytic and imparts this property to the surface. As a result, the surface of the negative hydrogen storage electrode is more catalytic and conductive than that surface contains a higher concentration of insulating oxide.

The surface of the negative electrode having a conductive and catalytic element--metal nickel--interacts with the metal hydroxide alloy in catalyzing the electrochemical charge and discharge reaction steps in addition to promoting rapid gas recombination.

Finally, the inventors of Ovonic Battery Company in the patent registration No. 5,616,432 ('432 patent) produced a Mg-Ni-Co-Mn alloy similar to the base alloy of the composite hydrogen storage material of the present invention. The storage capacity of this alloy was limited to about 2.7% by weight and none of the stored hydrogen was desorbed from the alloy at 30 ° C. Figure 1 shows the PCT curve of the thin film alloy (reference symbol Δ) of the '432 patent along with the PCT curve of the composite hydrogen storage material (reference symbol ◆). As can be seen, the hydrogen storage composite material of the present invention adsorbs at least 4% by weight of hydrogen, and even more noteworthy is that this hydrogen can be desorbed at a temperature of 30 ° C.

The present invention uses catalysis to reduce the desorption temperature of high capacity Mg based materials by promoting hydrogen adsorption / desorption on relatively pure Mg materials using insoluble catalyst materials and by incorporating several grain growth inhibitors.

The present invention provides a magnesium-based hydrogen storage material, including magnesium or magnesium-based hydrogen storage alloy; And a hydrogen desorption catalyst insoluble in the magnesium based hydrogen storage alloy and in the following form: 1) discontinuous dispersed regions of catalytic material in the bulk of the magnesium or magnesium based hydrogen storage alloy; 2) discontinuous dispersed regions on the particle surface of the magnesium or magnesium-based hydrogen storage alloy; 3) a continuous or semicontinuous layer of catalytic material on the surface of the magnesium or magnesium-based hydrogen storage alloy in bulk or in particle form; Or 4) combinations thereof. Preferably, the magnesium-based hydrogen storage alloy comprises at least 80 atomic percent magnesium and may comprise aluminum. Preferably, the hydrogen desorption catalyst comprises iron and further comprises one or more elements selected from the group consisting of B, Cu, Pd, V, Ni, C, Mn, Zr, Rb, Nb, Ti, U, and Sc can do.

The invention further includes a method of making a magnesium-based hydrogen storage material. One such method includes: a) mixing a powder of a magnesium or magnesium-based hydrogen storage alloy with a powder of a hydrogen desorption catalyst; b) compacting the mixed powder into a compact; And c) sintering / annealing the compact at a temperature between 450 ° C and 600 ° C. Preferably, the sintering / annealing step is carried out for at least 10 hours.

Another such method includes: a) forming a melt of powder of magnesium or magnesium-based hydrogen storage alloy and powder of hydrogen desorption catalyst in a protective atmosphere; b) stirring the melt to ensure a suspension of the insoluble powder of the hydrogen desorption catalyst in the molten magnesium or magnesium based hydrogen storage alloy; And c) rapidly cooling the stirred melt such that the suspended insoluble powder of the hydrogen desorption catalyst is well distributed in the solidified magnesium or magnesium-based hydrogen storage alloy.

Another method includes: a) mixing a powder of the magnesium or magnesium-based hydrogen storage alloy and a powder of the hydrogen desorption catalyst; And b) mechanically alloying the mixture in an attritor such that the powder particles of the hydrogen desorption catalyst are imbedded on at least the surface of the powder particles of the magnesium or magnesium-based hydrogen storage alloy. Preferably, heptane and carbon powder are used as grinding aids in the mechanical alloy of the mixture.

Further methods include: a) providing bulk or particulate magnesium or magnesium based hydrogen storage alloys; And b) depositing a continuous or semicontinuous layer of catalytic material on the surface of the bulk or particulate magnesium or magnesium-based hydrogen storage alloy by vapor deposition, electrolytic coating, or electroless coating. Preferably, the coating is formed by evaporation of the catalyst material and is about 100 mm thick.

The catalyst can be distributed in a complex manner by combining the above techniques. Bulk or particulate magnesium or magnesium based hydrogen storage alloys may be prepared by: a) forming a melt of the magnesium or magnesium based hydrogen storage alloy; And b) rapidly cooling said magnesium or magnesium-based hydrogen storage alloy by a bulk rapid cooling method. Useful bulk rapid cooling methods include melt spinning, centrifugal atomization, gas atomization, or water atomization.

1 is a scanning electron micrograph (SEM) taken in the back scattering mode of the hydrogen storage material of the present invention made of pure metal powder compacted and sintered at temperatures above 500 ° C. for 22 hours under vacuum.

2 is an X-ray diffraction pattern of the material of FIG. 1.

3 is a plot of the pressure-concentration-isothermal (PCT) curve for the material of FIG. 1 measured at 240 ° C.

4 shows the percent hydrogen uptake versus time (ie, rate of absorption) of the material of FIG. 1 at various temperatures.

FIG. 5 shows the percent of hydrogen desorbed versus time (ie, desorption rate) of the material of FIG. 1 at 240 ° C. FIG.

FIG. 6 shows a PCT curve of a sample having the same composition as that of FIG. 1 but sintered / annealed at 570 and 600 ° C., respectively.

FIG. 7 is an SEM back scattering micrograph of another material according to the present invention having the same composition as the material of FIG. 1 but formed by a mechanical alloy.

8 is an XRD plot of the material of FIG. 7.

9 is a plot of the PCT curve of the material of FIG. 7 measured at 240 ° C. FIG.

FIG. 10 shows the PCT absorption curves of the materials of FIG. 7 at 240 ° C., 210 ° C., 180 ° C., and 150 ° C. FIG.

FIG. 11 is an SEM back scattered micrograph of the cross section of a melt spun ribbon of a very uniform Mg-Al alloy used to make the material according to the present invention.

FIG. 12 shows a PCT plot of the hydrogen storage material according to the invention at 150 ° C., which is mechanically alloyed and pressed flat on an expanded nickel substrate and coated with 100 kPa on both sides of iron. It is prepared using.

13 is a comparative plot of the maximum reversible hydrogen storage capacity for the materials of FIGS. 1, 7, and 12 at various temperatures.

FIG. 14 is an SEM micrograph of a cross section of an ingot prepared by induction melting and casting of the elemental metal powder required to produce the composition of the material of FIG. 1, with continuous stirring of the melt to suspend the insoluble material. Let's do it.

15 is a schematic plot of the microstructure of a hydrogen storage powder material produced by various treatment methods of the present invention.

The inventors have found that iron and / or other elements with very low solubility in Mg to Mg based alloys inhibit grain growth of Mg or Mg based crystals in the alloy and catalyze the desorption of hydrogen from such Mg materials. . Accordingly, the present invention provides a magnesium-based hydrogen storage material in which hydrogen desorption is catalyzed by iron and / or other elements that are substantially insoluble in the magnesium-based hydrogen storage material. The insoluble catalyst material may be in the form of: 1) discontinuous dispersed regions of the catalyst material in the hydrogen storage material bulk; 2) discrete discrete regions on the particle surface of the hydrogen storage material; 3) a continuous or semicontinuous layer of catalytic material on the surface of the bulk or particulate hydrogen storage material; Or 4) combinations thereof. Catalytic materials include special rapid cooling methods; Or during the alloying process by a mechanical alloying method; The catalytic material may also be applied to the surface of the magnesium-based alloy by processes such as thermal evaporation, magnetic sputtering, or by electrolytic or electroless plating methods.

Elements that have little solid solubility in Mg can be used as grain growth inhibitors / desorption catalysts. Specific candidates include Fe (having a solubility of 0.00043 in%), Rb (having a solubility of less than 0.05 in%), Nb, Ti, V, and U. In addition, elements with limited solid solubility in magnesium can be used as part of an intermetallic compound having such elements to form grain boundary crystallite growth inhibiting material. Candidates include Mn (solubility in% in Mg = 0.99) and Zr (solubility in% in Mg = 1.042).

Example  One

Agate grind-molecules consisted of raw material consisting of pure metal powder of magnesium (99.8%, -325 mesh), aluminum (99.5%, -325 mesh), iron (99.9 +%, 10 microns), and other trace components. mortar-pestle). Ten different compositions were prepared and their compositions are shown in Table 1 in weight percent. A hardened steel die was used to squeeze the mixed powder into pellets 1 cm in diameter and 1 cm in length. The compacted pellets were placed in quartz tubes and sintered under vacuum at temperatures above 500 ° C. for 22 hours.

Table 1. Chemical Composition (all numbers are in weight percent)

Alloy number Mg Al Fe B Cu Pd V Ni C Sc MM-1 88.8 2.7 8.5 - - - - - - - MM-2 87 3 9 One - - - - - - MM-3 86 3 9 2 - - - - - - MM-4 86 3 9 - 2 - - - - - MM-5 87 3 6 - 4 - - - - - MM-6 87 3 8 - - 2 - - - - MM-7 87 3 8 - - - 2 - - - MM-8 87 - 9 - - - - 4 - - MM-9 87 - 9 - - - - - 4 - MM-10 87 3 7 - - - - - - 3

1 is a scanning electron micrograph (SEM) taken in the back scattering mode of a MM-1 sample sintered and annealed at 500 ° C. SEM shows phase separation of Fe and Al ₅ Fe ₂ intermetallic compounds embedded in the main Mg matrix. Fe and Fe-rich phases are about several microns in diameter and proximity is about 10-20 microns. 2 is an X-ray diffraction pattern of the sample recorded on the Rigaku Mini Flex. It clearly shows the coexistence of Fe and FeAl with the main Mg phase.

3 is a plot of the pressure-concentration-isothermal (PCT) curve for the material measured at 240 ° C. As can be seen, a very flat plateau pressure was found around 1800 Torr. Overall absorption / desorption has a maximum capacity at 5 wt.% Hydrogen and is reversible. 4 shows the percent hydrogen uptake versus time (ie, uptake rate) for MM-1 alloy materials at various temperatures. As shown in Figure 4, the absorption kinetics improves as the temperature increases. As can also be seen, the maximum storage capacity can be reduced if the absorption temperature is too high (see sample at 270 ° C.). Thus, finding an optimal absorption temperature seems to be a balance between kinetics and storage capacity. For MM-1 materials, it was found that an absorption temperature of about 240 ° C. was most optimal. At the maximum hydrogen supply pressure at 120-150 PSI, more than 90% of the hydrogen was absorbed within 2 hours. Higher hydrogen transfer pressures will further reduce the absorption process time. 5 shows the percent of time desorbed hydrogen of MM-1 versus time (ie, desorption rate) at 240 ° C. At this temperature, 90% of hydrogen was released in 1 hour.

Example  2

Another MM-1 material was prepared by the process described in Example 1 by varying the sinter / anneal temperature. 6 shows PCT curves of samples sintered / annealed at 570 and 600 ° C., respectively. The PCT of the material sintered / annealed at 570 ° C. shows little deviation from the PCT of the material of Example 1 (sintered / annealed at 500 ° C.), but the material sintered / annealed at 600 ° C. has a slightly higher pressure. Provides extended plateaus.

Example  3

A powder of mechanically alloyed (MA) MM-1 was prepared from a mixture of pure elemental magnesium (99.8%, -325 mesh), aluminum (99.5%, -325 mesh), and iron (99.9 +%, 10 microns). Milling was performed in a wear machine loaded with Cr-steel milling balls. A mechanical alloying process was performed under argon with the addition of 1% graphite and heptane to prevent material from sticking to the wearer wall. Typical milling time was 2 hours. 7 is an SEM back scattering micrograph of this sample. This figure shows severe phase segregation in the material. Region 1 (bright contrast in the figure) is filled with Fe and Al powders. On the other hand, region 2 (the darker region in the center) is all magnesium. 8 is an XRD plot of this sample and does not show an indication of the amorphous intermetallic product formed by this process. The MA-MM-1 powder was pressed onto an expanded nickel metal substrate and then coated on both sides with 100 kPa of iron by surface catalysis.

9 is a plot of the PCT curve for MA-MM-1 measured at 240 ° C. The pressure plateau is higher than the pressure plateau of sintered MM-1 due to the changed distance between the Mg-storage phase and the Fe-catalyst phase. Maximum hydrogen storage capacity increased from 5.0 to 5.7% and hydrogen was desorbed sufficiently at 240 ° C. FIG. 10 shows PCT absorption curves of MA-MM-1 samples at 240 ° C., 210 ° C., 180 ° C., and 150 ° C. FIG. The plateau pressure increases with temperature. This phenomenon is expected from heat-balance considerations. However, the maximum storage capacity decreases with decreasing temperature. This property is inconsistent with the thermal equilibrium model. We believe that this abnormality is due to the effect of temperature on absorption kinetics. In other words, PCT analysis was performed within certain time constraints, thus underestimating sufficient hydrogen storage capacity at lower temperatures. If more time was available to balance, higher peak capacities could be achieved than measured at these lower temperatures.

Example  4

Raw materials with the designed composition of MM-1, along with additional flux, were placed in an air-operated induction furnace to isolate the surface from the atmosphere and to prevent excess magnesium evaporation from the metal liquid. Extra argon gas was supplied to the crucible as an isolation blanket to prevent oxidation of the molten metal. After melting all the components in the crucible, the melt was poured obliquely into the mold and allowed to cool slowly to room temperature. The resulting composition of the ingot was examined by inductively coupled plasma (ICP) analysis and no traces of railroad were detected. From this comparative example, it can be seen that conventional induction melting techniques cannot include iron in the Mg bulk.

The Mg-Al ingot from above was placed in a bottom-poured melt-spinning machine. After raising the temperature above the melting point, the liquid was injected into a water-cooled copper wheel to change into a long ribbon. FIG. 11 is an SEM backscattered micrograph of the ribbon cross section showing a very uniform Mg-Al alloy. Thereafter, the ribbon was cut into small pieces and placed in a wear device for the same MA process as described in Example 3. Next, the ground powder was pressed onto a Ni expanded metal substrate and coated on both sides with Fe 100 mm 3.

MS + MA-MM-1 shows very good desorption kinetics at relatively low temperatures. 12 shows a PCT plot of this sample measured at 150 ° C. The observed absorption / desorption pressure hysteresis is due to the low measurement temperature. Nevertheless, the desorption plateau at 250 torr is very interesting. FIG. 13 compares the maximum reversible hydrogen storage capacity for three different processes (ie sinter, MA-only, MS + MA) at various temperatures. The MS + MA process gives the lowest desorption onset temperature (90 ° C.) as well as the lowest maximum reversible capacity due to the nonuniform distribution of the Fe phase. The MA-only sample shows the highest desorption onset temperature (150 ° C) but the highest reversible storage capacity.

Example  5

A raw material having a predetermined composition of MM-1, along with additional flux, was placed in an air induction furnace to isolate the melt surface from the atmosphere and to prevent excess magnesium evaporation from the metal liquid. Extra argon gas was supplied to the crucible as an isolation blanket to prevent oxidation of the metal. The molten alloy was stirred manually to uniformly suspend FeAl and Fe phases that were not mixed in the liquid. The liquid was poured obliquely into an quenched mold cooled by water through an argon protected ladle to incorporate FeAl and Fe phases into the final product. 14 is a SEM micrograph of the cross section of the resulting ingot showing a uniform distribution of FeAl and Fe secondary phases in the Mg host matrix. The Fe-containing is about 1 micron in size. ICP analysis is consistent with the presence of Fe and Al in the ingot. With moderate agitation in liquids such as secondary stirring coils, inert gas bubbling, rotary crucibles, and the like, other bulk rapid cooling such as melt spinning, centrifugal atomization, gas atomization, water atomization, can achieve similar results. 15 is a schematic illustration of the microstructure of a hydrogen storage powder material produced by various treatment methods of the present invention. All methods can make reversible hydrogen storage at substantially lower temperatures than the prior art.

The drawings, discussion, description, and examples herein merely illustrate particular embodiments of the invention and are not meant to be limiting in its practice. It is the following claims, including all equivalents, that define the scope of the invention.

Claims (22)

Magnesium or magnesium-based hydrogen storage alloys; Magnesium-based hydrogen storage material comprising a hydrogen desorption catalyst, And the hydrogen desorption catalyst is insoluble in the magnesium-based hydrogen storage alloy and is in the form of magnesium-based hydrogen storage material. 1) discontinuous dispersed regions of catalytic material in the bulk of the magnesium or magnesium-based hydrogen storage alloy; 2) discrete discrete regions on the particle surface of the magnesium or magnesium-based hydrogen storage alloy; 3) a continuous or semicontinuous layer of catalytic material on the surface of said magnesium or magnesium-based hydrogen storage alloy in bulk or particulate form; or 4) a combination of these. The method of claim 1, And the magnesium-based hydrogen storage alloy comprises at least 80 atomic percent magnesium. The method of claim 2, The magnesium-based hydrogen storage alloy further comprises aluminum. The method of claim 1, The hydrogen desorption catalyst is magnesium-based hydrogen storage material, characterized in that containing iron. The method of claim 4, wherein The hydrogen desorption catalyst further comprises one or more elements selected from the group consisting of B, Cu, Pd, V, Ni, C, Mn, Zr, Rb, Nb, Ti, U, and Sc. Storage material. The method of claim 1, And the hydrogen desorption catalyst comprises a discontinuous dispersed region of catalyst material in the bulk of the magnesium or magnesium based hydrogen storage alloy. The method of claim 6, The magnesium-based hydrogen storage material, a) mixing the powder of the magnesium or magnesium-based hydrogen storage alloy and the powder of the hydrogen desorption catalyst; b) compacting the mixed powder into a compact; And c) a magnesium-based hydrogen storage material formed by sintering / annealing the compact at a temperature between 450 ° C. and 600 ° C .: The method of claim 7, wherein And the sintering / annealing step is performed for at least 10 hours. The method of claim 6, The magnesium-based hydrogen storage material, a) forming a melt of the powder of the magnesium or magnesium-based hydrogen storage alloy and the powder of the hydrogen desorption catalyst in a protective atmosphere; b) stirring the melt to ensure a suspension of the insoluble powder of the hydrogen desorption catalyst in the molten magnesium or magnesium based hydrogen storage alloy; And c) rapidly cooling the stirred melt such that the suspended insoluble powder of the hydrogen desorption catalyst is well distributed in the solidified magnesium or magnesium-based hydrogen storage alloy. The method of claim 1, And the hydrogen desorption catalyst comprises a discrete dispersed region on the particle surface of the magnesium or magnesium-based hydrogen storage alloy. The method of claim 10, The magnesium-based hydrogen storage material, a) mixing the powder of the magnesium or magnesium-based hydrogen storage alloy and the powder of the hydrogen desorption catalyst; And b) mechanically alloying the mixture in an attritor such that the powder particles of the hydrogen desorption catalyst are imbedded on at least the surface of the powder particles of the magnesium or magnesium-based hydrogen storage alloy. Magnesium-based hydrogen storage material characterized in that. The method of claim 10, Magnesium-based hydrogen storage material, characterized in that heptane and carbon powder are used as grinding aids during the mechanical alloying of the mixture. The method of claim 1, And said hydrogen desorption catalyst comprises a continuous or semicontinuous layer of catalytic material on the surface of said magnesium or magnesium based hydrogen storage alloy in bulk or particulate form. The method of claim 13, The magnesium-based hydrogen storage material, a) providing bulk or particulate magnesium or magnesium based hydrogen storage alloys; And b) magnesium formed by depositing a continuous or semicontinuous layer of catalyst material on the surface of the bulk or particulate magnesium or magnesium-based hydrogen storage alloy by deposition, electrolytic coating, or electroless coating Hydrogen storage materials. The method of claim 14, And depositing a continuous or semicontinuous layer of catalyst material on the surface of the bulk or particulate magnesium or magnesium-based hydrogen storage alloy comprises evaporation of the catalyst material. The method of claim 13, Magnesium-based hydrogen storage material, characterized in that the continuous or semicontinuous layer of the catalyst material is about 100 GPa thick. The method of claim 14, Providing the bulk or particulate magnesium or magnesium based hydrogen storage alloy comprises bulk or particulate magnesium or magnesium based hydrogen storage having a hydrogen desorption catalyst disposed in discrete dispersed regions within the bulk or particulate magnesium or magnesium based hydrogen storage alloy. Magnesium-based hydrogen storage material comprising providing an alloy. The method of claim 17, Providing the bulk or particulate magnesium or magnesium-based hydrogen storage alloy, a) mixing the powder of the magnesium or magnesium-based hydrogen storage alloy and the powder of the hydrogen desorption catalyst; b) compacting the mixed powder into a compact; And c) sintering / annealing the compact at a temperature between 450 ° C and 600 ° C. The method of claim 18, The sintering / annealing step is performed for at least 10 hours. The method of claim 17, Providing the bulk or particulate magnesium or magnesium-based hydrogen storage alloy,  a) forming a melt of the powder of the magnesium or magnesium-based hydrogen storage alloy and the powder of the hydrogen desorption catalyst in a protective atmosphere; b) stirring the melt to ensure a suspension of insoluble powder of a hydrogen desorption catalyst in the molten magnesium or magnesium based hydrogen storage alloy; And c) rapidly cooling the stirred melt such that the suspended insoluble powder of the hydrogen desorption catalyst is well distributed in the solidified magnesium or magnesium based hydrogen storage alloy. The method of claim 14, Providing the bulk or particulate magnesium or magnesium-based hydrogen storage alloy, a) forming a melt of said magnesium or magnesium-based hydrogen storage alloy; And b) rapidly cooling said magnesium or magnesium-based hydrogen storage alloy by a bulk rapid cooling method. The method of claim 21, The bulk rapid cooling method includes magnesium spinning, melt spinning, centrifugal atomization, gas atomization, or water atomization.

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