JP2007522917A - Catalytic hydrogen desorption in a Mg-based hydrogen storage material and method for producing the material - Google Patents

Abstract

Magnesium or a magnesium-based hydrogen storage alloy, insoluble in the magnesium-based hydrogen storage alloy, 1) an independent dispersion region of the catalytic material in the bulk of the magnesium or magnesium-based hydrogen storage alloy, 2) the magnesium or Independent dispersed regions on the particle surface of the magnesium-based hydrogen storage alloy, 3) Continuous or semi-continuous layers of the catalytic material on the surface of the magnesium or magnesium-based hydrogen storage alloy in bulk or particulate form, or 4) A magnesium-based hydrogen storage material comprising a hydrogen desorption catalyst in the form of a combination thereof. A method of manufacturing this material is also disclosed.
[Selection] Figure 9

Description

  The present invention relates generally to hydrogen storage materials, and more specifically, magnesium-based hydrogen storage materials, wherein hydrogen desorption is catalyzed by a substance that is insoluble in the magnesium-based hydrogen storage material. About. This insoluble catalytic material is composed of 1) an independent dispersion region of the catalytic material in the bulk of the hydrogen storage material, 2) an independent dispersion region on the particle surface of the hydrogen storage material, and 3) a surface of the bulk or particulate hydrogen storage material. It may be in the form of a continuous or semi-continuous layer of the catalytic material above, or 4) combinations thereof.

  Increasing energy demand is to consider that traditional energy sources such as coal, oil or natural gas are not inexhaustible, or at least they will continue to become increasingly expensive and replace them with hydrogen Is encouraging professionals on the road to recognize that it is wise.

  Hydrogen, for example, can be used as a fuel for an internal combustion engine instead of a hydrocarbon. In this case, there is an advantage that there is no air pollution due to formation of oxides of carbon, nitrogen and sulfur when hydrocarbons burn. Hydrogen can also be used to burn into a hydrogen-air fuel cell to generate the electricity required for an electric motor.

  One of the problems posed by the use of hydrogen is its storage and transport. Many solutions have been presented.

  Although hydrogen can be stored in steel cylinders under high pressure, this method has the disadvantage of requiring dangerous and heavy containers that are difficult to handle (in addition to the low storage capacity of about 1% by weight). Hydrogen can also be stored in cryogenic storage containers, but this involves the disadvantages associated with the use of cryogenic liquids, such as expensive containers that also require careful handling. There is also a “boil off” loss of about 2-5% daily.

  Another method of storing hydrogen is to store it in the form of a hydride, which is decomposed and supplied at an appropriate time after storage. As described in French Patent 1,529,371, hydrides of iron-titanium, lanthanum-nickel, vanadium, and magnesium are used for this purpose.

  Since this first discovery that hydrogen can be stored in a safe and small solid state metal hydride form, researchers have strived to produce hydrogen storage materials with optimal properties. In general, the ideal material properties that these researchers are trying to achieve are: 1) large hydrogen storage capacity, 2) lightweight materials, 3) suitable hydrogen absorption / desorption temperatures, 4) suitable 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.

MgH ₂ -Mg system has the highest weight percent of the theoretical capacity of the hydrogen storage (7.65 wt%), therefore, the highest theoretical energy density per unit weight of the storage material (2332Wh / kg; Reilly & Sandrock, Spectrum der Wissenshaft, Apr. 1980, 53) is the most suitable of all known metal hydrides and metal systems that can be used as reversible hydrogen storage systems.

This characteristic and the relatively low price of magnesium are considered to be the optimal hydrogen storage system for transporting the MgH ₂ -Mg system, but for hydrogen powered vehicles, the reaction rate is unsatisfactory and so far It is preventing it from being used. For example, it is known that pure magnesium can be hydrogenated only under extreme temperature conditions, perhaps 400 ° C., and only very slowly and incompletely. The dehydrogenation rate of the resulting hydride is also unsuitable as a hydrogen storage material (Genossar & Rudman, Zf Phys. Chem., Neue Folg 116, 215 [1979], and references cited therein). .

  Furthermore, the hydrogen storage capacity of the magnesium storage material decays during the fill / release cycle. This phenomenon can be explained by the progress of surface contamination that prevents the magnesium atoms located inside the material from accessing hydrogen during charging.

  To release hydrogen in conventional magnesium or magnesium / nickel storage material systems, temperatures above 250 ° C. are required, which is accompanied by a large supply of energy at the same time. The high temperature levels and high energy required to release hydrogen result, for example, in that a vehicle with an internal combustion engine cannot be operated with these alloys alone. This is because the energy contained in the exhaust gas is only sufficient to meet 50% of the hydrogen requirement of an internal combustion engine from magnesium or a magnesium / nickel alloy, even when it is most convenient (full load). To occur. Therefore, the remaining hydrogen demand must be obtained from other hydride alloys. For example, the alloy can be titanium / iron hydride (typical low temperature hydride storage) that can operate at temperatures below 0 ° C. These low temperature hydride alloys have the disadvantage of low hydrogen storage capacity.

Storage materials have been developed in the past that have a relatively large storage capacity but nevertheless have a hydrogen release temperature of up to about 250 ° C. U.S. Pat. No. 4,160,014 describes the formula Ti _[1-x] Zr _[x] Mn _[2-yz] Cr _[y] V _{[z] where} x = 0.05 to 0. 4, y = 0 to 1 and z = 0 to 0.4). Up to about 2% by weight of hydrogen can be stored in such alloys. In addition to this relatively small storage capacity, these alloys also have the disadvantage that the price of the alloy is very expensive when metal vanadium is used.

  Further, U.S. Pat. No. 4,111,689 discloses a storage alloy containing 31 to 46% by weight titanium, 5 to 33% by weight vanadium and 36 to 53% by weight iron and / or manganese. . This type of alloy has a larger hydrogen storage capacity than the alloy according to US Pat. No. 4,160,014, which is incorporated herein by reference, but they require a temperature of at least 250 ° C. to completely release hydrogen. It has the disadvantage of being. At temperatures up to about 100 ° C., in the best case, about 80% of the hydrogen content can be released. However, since the heat required to release hydrogen from hydride storage is often only available at low temperature levels, high release capabilities are frequently required in the industry, especially at low temperatures.

In contrast to other metals or metal alloys, especially those containing titanium or lanthanum, magnesium-containing metal alloys not only have a low material cost, but also because of their low specific gravity as their storage material, Is preferable. However,
Mg + H ₂ → MgH ₂
This hydrogenation is more difficult to achieve with magnesium. This is because the surface of magnesium generally oxidizes rapidly in air to form a stable MgO and / or Mg (OH) ₂ surface layer. These layers inhibit the dissociation of hydrogen molecules as well as the absorption of the generated hydrogen atoms and the diffusion of hydrogen atoms from the particle surface into the volume of the magnesium storage material.

Magnesium's hydrogenation capacity is measured using aluminum (Douglas, Metall. Trans. 6a, 2179 [1975]), indium (Mintz, Gavra & Hadari, J. Inorg. Nucl. Chem. 40, 765 [1978]), or iron. (Welter & Rudman, Scripta Metallurgica 16 , 285 [1982]) individual foreign metals such as, or different foreign metal (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. Intensive efforts have recently been made to improve by doping or alloying with intermetallic compounds such as aNi ₅ (Tanguy et al., Mater. Res. Bull. 11, 1441 [1976]). Has been made.

Although these attempts have somewhat improved their reaction rates, some of the essential drawbacks have not been removed from the resulting product. Initial hydrogenation of magnesium doped with foreign metals or intermetallics still requires harsh reaction conditions and the reaction rate of the system is only satisfactory after many hydrogenation and dehydrogenation cycles and is reversible The hydrogen content is increased. A significant percentage of foreign metals or expensive intermetallics are also required to improve the reaction rate. Furthermore, the storage capacity of such systems is generally well below what is theoretically expected for MgH ₂ .

It is known that the storage properties of magnesium and magnesium alloys can also be enhanced by the addition of substances that can help destroy stable magnesium oxides. For example, such an alloy is Mg ₂ Ni, which seems to form an unstable oxide. Thermodynamic considerations have shown that this alloy can be extended to nickel metal inclusions that catalyze the hydrogen dissociation-absorption reaction by surface reaction Mg ₂ Ni + O ₂ → 2MgO + Ni. A. Seller et al. , Journal of Less-Common Metals 73, 1980, pages 193 and below.

  One possible catalyst for the hydrogen dissociation-absorption reaction on the magnesium surface is also in the formation of a two-phase alloy where one phase is a hydride former and the other phase is a catalyst. Thus, it is known to use nickel-plated magnesium as a hydrogen storage material. F. G. Eisenberg et al. See Journal of Less-Common Metals 74, 1980, pages 323 et seq. However, there are problems encountered while depositing and dispersing nickel across the magnesium surface.

In order to obtain a very dense and good adhesion catalyst layer only by forming an equilibrium phase, it is possible to use a eutectic mixture of magnesium and magnesium copper (Mg ₂ Cu) as a hydride forming phase for hydrogen storage It is also known that it can be done. J. et al. Genossar et al. , Zeitschiff for Physikalische Chemie Neue Folg 116, 1979, pages 215 et seq. However, the storage capacity per unit volume of material achieved by the magnesium-containing particles cannot meet the high demand due to the amount of magnesium copper required for the eutectic mixture.

  Scientists at that time examined various materials and assumed that a specific crystal structure was required for hydrogen storage. For example, “Hydrogen Storage in Metal Hydride”, Scientific American, Vol. 242, no. 2, pp. 118-129, February, 1980. It has been found that many of the disadvantages of prior art materials can be overcome by utilizing different types of materials, namely disordered hydrogen storage materials. For example, US Pat. No. 4,265,720 for “Storage Materials for Hydrogen” by Guenter Winstel describes amorphous or microcrystalline silicon hydrogen absorbers. Silicon is preferably a book film on the substrate in combination with a suitable catalyst.

  JP 55-167401, “Hydrogen Storage Material” in the name of Matsumoto et al. Discloses a two-component or three-component hydrogen storage material having an amorphous structure of at least 50 volume percent. The first component is selected from the group of Ca, Mg, Ti, Zr, Hf, V, Nb, Ta, Y and lanthanide, and the second component is the group of Al, Cr, Fe, Co, Ni, Cu, Mn and Si Selected from. A third component from the group of B, C, P and Ge may optionally be present. According to the teaching of JP 55-167401, an amorphous structure is necessary to overcome the disadvantages of the disadvantageous high desorption temperature characteristics of most crystalline systems. High desorption temperatures (eg, 150 ° C. and above) severely limit the range of possible applications for the system.

  According to Matsumoto et al., At least 50% of amorphous material is not uniform, unlike the case of crystalline materials, because the bonding energy of individual atoms is not uniform and it is distributed over a wide range, so at least some hydrogen is compared It is possible to desorb at a low temperature.

  Matsumoto et al. Claim at least 50% of materials with an amorphous structure. Matsumoto et al. Do not teach any further about the meaning of the term “amorphous”, but the scientifically accepted definition of the term is short-range order that ranges up to about 20 angstroms or less. means.

  The use of amorphous structural materials to achieve better desorption kinetics utilizing the non-flat hysteresis curve of Matsumoto et al. Is an inadequate and partial solution. Other problems found in crystalline hydrogen storage materials remain, especially the low useful hydrogen storage capacity at moderate temperatures.

  However, even better hydrogen storage results, i.e., long cycle life, good mechanical strength, low absorption / desorption temperatures and pressures, reversibility, and resistance to chemical contamination are This can be realized if all the benefits of modifying the hydrogen storage material are adopted. Modification of disordered structurally metastable hydrogen storage materials is described by Stanford R., et al. Ovshinsky et al., “Hydrogen Storage Materials and Methods of Making the Same,” U.S. Pat. No. 4,431,561. As described therein, a disordered hydrogen storage material characterized by a chemically modified and thermodynamically metastable structure would have all the hydrogen storage properties desirable for a wide range of commercial applications. Can be designed to The modified hydrogen storage material can be designed and manufactured to have a larger hydrogen storage capacity than the single phase crystalline host material. The strength of the chemical bond between hydrogen and the storage sites in these modified materials should be designed to provide a wide range of possible bond force distributions, thereby providing the desired absorption and desorption properties. Can do. Chemically modified, disordered hydrogen storage materials with a thermodynamically metastable structure also greatly increase the density of catalytically active sites resulting in improved hydrogen storage reaction rates and increased resistance to contamination. It has increased.

  The synergistic combination of selected modifiers incorporated into the selected host matrix is the amount of structural and chemical modification that stabilizes the chemical, physical, and electronic structures and forms that facilitate hydrogen storage. Achieve quality together.

  The framework of the modified hydrogen storage material is a lightweight host matrix. The host matrix is structurally modified with selected modifier components to provide a disordered material with a local chemical environment that provides the necessary hydrogen storage properties.

  Another advantage of the host matrix described by Ovshinsky et al. Is that the modifier can be modified using varying proportions of its components in an almost continuous range. This capability allows the host matrix to be engineered with a modifier and a hydrogen storage material with properties suitable for a particular application to be designed or processed according to requirements. This is in contrast to multi-component single phase host crystalline materials where the available stoichiometric range is very limited. Therefore, it is impossible to control the chemical and structural modification of the thermodynamic properties and reaction rate of such crystalline materials in a continuous range.

  A further advantage of these disordered hydrogen storage materials is that they are even more resistant to contamination. As mentioned above, these materials have a higher density of catalytic active sites. Thus, some of such sites can be sacrificed for the effects of contaminating species while many non-contaminating active sites can still continue to provide the desired hydrogen storage rate.

  Another advantage of these disordered materials is that they can be designed to be mechanically more flexible than single phase crystalline materials. Thus, the disordered material can be more strained during expansion and contraction, which allows for higher mechanical stability during absorption and desorption cycles.

  One of the disadvantages of these disordered materials is that some of the Mg-based alloys have heretofore been difficult to manufacture. In particular, a material that does not form a co-solution in the molten state. Moreover, the most promising materials (ie, magnesium-based materials) have been extremely difficult to manufacture in bulk form. That is, a small amount of these disordered alloys can be produced by a thin film sputtering technique, but a bulk preparation technique has not existed.

  In the mid 1980s, two groups developed mechanical alloying techniques to produce hydrogen storage materials for bulk disordered magnesium alloys. Mechanical alloying has been found to allow alloying of components with very different vapor pressures and melting points (eg Mg and Fe or Ti, etc.), especially in the absence of a stable intermetallic phase. . Conventional techniques such as induction melting have been found unsuitable for such purposes.

  The first of the two groups was a team of French scientists studying mechanical alloying of Mg-Ni based 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 (a binary mechanical alloy of Mg and Ni incorporating 0, 10, 25, and 55 wt% Ni), and also Song, et al. “Hydriding and Dehydrating Characteristics of Mechanically Alloyed Mixtures Mg-x wt% Ni (x = 5, 10, 25 and 55)”, Journal of the Less Ms. Comm. 131, 1987, pp. See 71-79 (a binary mechanical alloy of Mg and Ni incorporating 5, 10, 25, and 55 wt% Ni).

  The second of the two groups was a team of Russian scientists who studied 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”, Doklide Physical Chemistry (England Translation) vol. 286: 1-3, 1986, pp. 55-57 (a binary mechanical alloy of Mg and Ni, Ce, Nb, Ti, Fe, Co, Si and Q), and Ivanov, et al. “Magnesium Mechanical Alloys for Hydrogen Storage”, Journal of the Less-Common Metals, vol. 131, 1987, pp. 25-29 (a binary mechanical alloy of Mg and 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 (Mg-Ni based binary mechanical alloy). A collaborative study between these French and Russian groups, Konstanchuk, et al. , “The Hydriding Properties of a Mechanical Alloy With Composition Mg-25% Fe”, Journal of the Less-Common Metals, vol. 131, 1987, pp. See also 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) studied the hydrogen storage properties of mechanical alloys of magnesium and metal oxides. Khrussanova, et al. , “Hydriding Kinetics of Mixtures Containing Some 3d-Transition Metal Oxides and Magnesium, Zeitschrift for Physiqueol Chemieol. 164, 1989, pp. 1261- 1266 (binary mixture of Mg and _{TiO 2,} V 2 _{O 5,} and _Cr 2 _{O 3} and comparison of mechanical alloying), and Peshev, et al. "Surface Composition of Mg--TiO ₂ Mixtures for Hydrogen Storage, Prepared by Different Methods", Materials Research Bulletin, vol. 24, 1989, pp. 207-212 (comparison of conventional mixtures and mechanical alloys of Mg and TiO ₂ ). Khrussanova, et al. , “On the Hydraulics of a Mechanically Alloyed Mg (90%) — V ₂ O ₅ (10%) Mixture”, International Journal of Hydrogen Energy, vol. 15, no. 11, 1990, pp. 799-805 (study of the hydrogen storage properties of a binary mechanical alloy of Mg and _V 2 _{O 5),} and Khrussanova, et al. , “Hydriding of Mechanically Alloyed Mixtures of Magnitude With MnO ₂ , Fe ₂ O ₃ , and NiO”, Materials Research Bulletin, vol. 26, 1991, pp. 561-567 (Mg and _MnO 2, _Fe 2 _{O 3,} and the study of hydrogen storage properties of a binary mechanical alloys of NiO) See also. Finally, Khrussanova, et al. , “The Effect of the d-Electron Concentration on the Absorption Capacity of Some Systems for Hydrologic Storage”, Materials Research Bulletin. 26, 1991, pp. 1291-1298 (study of high-density d-electron 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 Hybridized Alloyed Mixed of Magnitude and Iron (III) Oxide”, Materials Research Bulletin, Vol. 27, 1992, pp. See also 905-910 (Study of hydrogen storage properties of binary mechanical alloys of Mg and Fe ₂ O ₃ ).

More recently, a group of Chinese scientists have studied the hydrogen storage properties of some mechanical alloys of Mg and other metals. Yang, et al. , “The Thermal Stability of Amorphous Hydride Mg ₅₀ Ni ₅₀ H ₅₄ and Mg ₃₀ Ni ₇₀ H ₄₅ ”, Zeitschiff fur Physiklishe Chemie, Munch. 183, 1994, pp. 141-147 (a study of the hydrogen storage properties of mechanical alloys Mg ₅₀ Ni ₅₀ and Mg ₃₀ Ni ₇₀ ), Lei, et al. , “Electrochemical Behavior of Some Mechanically Alloyed Mg-Ni-based Amorphous Storage Storage Alloys”, Zeitschrift fur Physichemis. 183, 1994, pp. 379-384 (Study of electrochemical [ie, Ni-MH battery] properties of several mechanical alloys of Mg-Ni and Co, Si, Al, Co-Si).

  Short range order, or local order, is described in detail in Ovshinsky, U.S. Pat. No. 4,520,039, entitled Compositionally Changed Materials and Methods for Synthesizing the Materials. The contents of which are incorporated by reference. This patent states that disordered materials do not require any periodic local ordering, and allow for spatial and directional arrangement of similar or different atoms or groups of atoms with higher accuracy and control of the local arrangement. As a result, it has been disclosed that a novel phenomenon can be generated quantitatively. In addition, this patent does not require the atoms used to be limited to “d-band” or “f-band” atoms, but to artificially influence the physical properties of the material and thus the function of the material. It is discussed that the interaction aspect with the local environment and / or electron orbital overlap can be any atom that plays an important role physically, electronically or chemically. The components of these materials offer various bondability due to the multi-directional nature of the d-electron orbitals. The multi-directionality of d-electron orbitals (“pocupine effect”) results in a significant increase in density and hence active site. These techniques provide a means to synthesize new materials that are disordered in several different forms at the same time.

Ovshinsky has previously shown that the number of surface sites can be significantly increased by creating an amorphous film whose bulk resembles a relatively pure material that is desirable. Ovshinsky also used multiple components to gain increased chemical bonding and local environmental order that allowed the material to achieve the required electrochemical characteristics. Principals and Applications of Amorphicity, Structural Change, and Optical Information Encoding, 42 Journal De Physique at C4-1096 (October in 198)
“Amorphous is a general term that refers to the lack of X-ray diffraction patterns that demonstrate long-range periodicity and is not a sufficient description of the material. Some things to consider to understand amorphous materials The result is the type of chemical bond, the number of bonds produced by local order, ie its coordination number, and the entire chemical and geometric local environment. Amorphous is not created by thinking of atoms as hard spheres and randomly filling them, but amorphous solids are simply randomly embedded with atoms. Amorphous materials should be viewed as being composed of an interactive matrix in which the electronic configuration is generated by forces generated by free energy, which includes the chemical nature of the constituent atoms and By coordination It can be defined physically, using multi-electron orbital atoms as components and using various preparation techniques to inhibit the progress of normal relaxation phenomenon to return to equilibrium state, and the amorphous state Because it has three-dimensional freedom, it is possible to create a completely new type of amorphous material-chemically modified material ... "
Once amorphous is understood as a means of introducing surface sites into the membrane, all kinds of consequences such as porosity, topological properties, crystallinity, site characteristics, and distance between sites, etc. It is now possible to generate “disorders” that take into account. Rather than exploring material changes that maximize the surface bonds and surface disorder that occur accidentally in materials with ordered crystal structures, Ovshinsky and his team at ECD “We began building materials, where we artificially designed the desired disorder. See US Pat. No. 4,623,597, the disclosure of which is incorporated herein by reference.

  The term “disordered” as used herein to refer to an electrochemical electrode material corresponds to the meaning of the term used in the literature, for example:

          A disordered semiconductor can exist in several structural states. This structural element is [material]. . . Construct a new variable that can control the physical properties of Furthermore, structural disorder opens up the possibility of preparing new compositions and mixtures in a metastable state that far exceed the limits of thermodynamic equilibrium. Therefore, we note the following points as further distinguishing features. Many disordered [materials]. . . In, control the short-range order parameter, thereby forcing a new coordination number to the component. . . It is possible to achieve dramatic changes in the physical properties of these materials, including

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

  “Short range order” of these disordered materials is described by Ovshinsky in The Chemical Basis of Amorphity: Structure and Function, 26: 8-9 Rev. Room. Phys. at 893-903 (1981).

“Short-range order is not a conserved quantity ... In fact, when the symmetry of the crystal is broken, it is impossible to maintain the same short-range order. It is controlled by a force field and therefore the environment must be radically different in the corresponding crystalline and amorphous solids, in other words it is a local chemical bond and the electrical, chemical, and These are interactions with their surrounding environment that determine physical properties, and these cannot be the same in amorphous materials as when they are crystalline materials ... 3D space of amorphous materials Electron orbital relationships that can exist within but not in crystalline materials are the basis for new geometrical considerations, many of which are inherently anti-crystalline in the natural state. Is a single component However, to fully understand the amorphous nature, it generates internal topological properties that are incompatible with the translational symmetry of the crystal lattice. Therefore, it is necessary to understand the essential three-dimensional relationship in the amorphous state, what is important in the amorphous state is that it does not have any crystalline counterpart and is mainly similar in chemical composition. The fact is that infinite materials can be made that are not even the spatial and energetic relationships of these atoms, even though their chemical constituents may be the same, the amorphous and crystalline forms Can be quite different ... "
Based on the principles of the disordered material described above, three types of highly efficient electrochemical hydrogen storage cathode materials were formulated. These types of cathode materials are individually and collectively referred to below as “Ovonic”. The first type is a La-Ni _5- type cathode material, which has recently become a disordered multi-component alloy, i.e., "ovonic", rare earth elements such as Ce, Pr, Nd and other metals, For example, it is significantly modified by the addition of Mn, Al, and Co. The second type is a Ti—Ni type cathode material, which is introduced and developed by the assignee of the present invention and is a disordered multi-component alloy, ie “ovonic”, transition metal, eg Zr. , V and other metallic modifier components such as Mn, Cr, Al, Fe, etc. are significantly modified. The third is a disordered polymorphism described in US Pat. Nos. 5,506,069, 5,616,432, and 5,554,456, the disclosures of which are incorporated herein by reference. Component MgNi type cathode material.

Based on the principles expressed in the Ovshinsky '597 patent, the Ovonic Ti-V-Zr-Ni type active material is disclosed in U.S. Pat. Incorporated herein by reference). The second kind of ovonic material reversibly forms a hydride because of hydrogen storage. All materials used in the '400 patent use a Ti-V-Ni composition and contain at least Ti, V, and Ni, which are present with at least one or more of Cr, Zr, and Al. The materials of the '400 patent are generally multiphase polycrystalline materials, including but not limited to C ₁₄ and C ₁₅ . One or more phases of Ti-V-Zr-Ni material having a type crystal structure may be included. Other Ovonic Ti-V-Zr-Ni alloys include improved charge retention electrochemical hydrogen storage alloys and improved charge retention electrochemical hydrogen storage alloys and enchanted charge energies. Commonly assigned US Pat. No. 4,728,586 (the '586 patent), the disclosure of which is incorporated by reference.

  The characteristic surface roughness of the metal electrolyte interface is commonly assigned, US Pat. No. 4,716,088 to Reichman, Venkatesan, Fetcenko, Jeffries, Stahl, and Bennet, the disclosure of which is incorporated by reference. As a result of the disorder of the material. In addition to many alloys and their phases, all constituents are present throughout the metal, so they are also exposed to cracks formed at the surface and at the metal / electrolyte interface. Thus, the characteristic surface roughness is a manifestation of the interaction of the physical and chemical properties of the host material with the alloy and the crystalline phase of the alloy in an alkaline environment. Chemical, physical, and crystallographic parameters at the microscopic level of the individual phases within the hydrogen storage alloy material are important in determining its macroscopic electrochemical characteristics.

  In addition to the physical properties of the roughened surface, it has been observed that V-Ti-Zr-Ni type alloys tend to reach a steady state in surface state and grain size. This steady state surface condition is characterized by a relatively high concentration of metallic nickel. These observations are consistent with the relatively rapid removal of titanium and zirconium oxides from the surface by precipitation and the slower dissolution rate of nickel. The resulting surface has a higher concentration of nickel than expected from the bulk composition of the hydrogen storage cathode. Nickel in the metallic state is conductive and catalytic and imparts these properties to the surface. As a result, the surface of the hydrogen storage cathode is more catalytic and conductive than when the surface contains a higher concentration of insulating oxide.

  Cathodic surface with metallic nickel, a conductive and catalytic component, facilitates fast gas recombination in addition to catalyzing electrochemical charging and discharging processes through interaction with metal hydride alloys To do.

  Finally, in US Pat. No. 5,616,432 (the '432 patent), researchers at Ovonic Battery Company manufactured an Mg—Ni—Co—Mn alloy similar to the basic alloy of the composite hydrogen storage material of the present invention. did. The storage capacity of these alloys was limited to about 2.7 weight percent, and no stored hydrogen was desorbed from the alloys at 30 ° C. FIG. 1 plots the PCT curve of the '432 patent thin film alloy (symbol Δ) along with that of the composite hydrogen storage material (symbol ◆) of the present invention. As can be seen, the hydrogen storage composite material of the present invention absorbs more than 4 weight percent of hydrogen, and it should be noted that this hydrogen can be desorbed at a temperature of 30 ° C.

  The present invention uses a catalyst to promote hydrogen absorption / desorption in relatively pure Mg material with an insoluble catalytic material, and some particle growth inhibition of the desorption temperature of large volume Mg-based materials It is lowered by adding an agent.

  The present invention relates to magnesium or a magnesium-based hydrogen storage alloy, and is insoluble in the magnesium-based hydrogen storage alloy, and 1) independent dispersion of the catalytic material in the bulk of the magnesium or magnesium-based hydrogen storage alloy 2) Independent dispersion regions on the surface of the magnesium or magnesium-based hydrogen storage alloy particles, 3) Continuous or semi-catalytic material on the surface of the magnesium or magnesium-based hydrogen storage alloy in bulk or granular form A magnesium-based hydrogen storage material comprising a hydrogen desorption catalyst in the form of a continuous layer, or 4) combinations thereof, is provided. Preferably, the magnesium-based hydrogen storage alloy includes at least 80 atomic percent magnesium and may also include aluminum. Preferably, the hydrogen desorption catalyst comprises iron and is one or more selected from the group consisting of B, Cu, Pd, V, Ni, C, Mn, Zr, Rb, Nb, Ti, U and Sc Can be included.

  The present invention further includes a method for producing a magnesium-based hydrogen storage material. One such method is: a) mixing magnesium or magnesium-based hydrogen storage alloy powder and hydrogen desorption catalyst powder; b) compressing the mixed powder into a compact; c) the compact Sintering / annealing the body at a temperature of 450 ° C to 600 ° C. Preferably, the sintering / annealing is performed for at least 10 hours.

  Another production method includes: a) forming a melt of magnesium or magnesium-based hydrogen storage alloy powder and hydrogen desorption catalyst powder in a protective atmosphere; and b) stirring the melt to form molten magnesium or magnesium. Ensure suspension of insoluble powder of hydrogen desorption catalyst in base hydrogen storage alloy, and c) Insoluble powder of hydrogen desorption catalyst in solid phase magnesium or magnesium-based hydrogen storage alloy Quenching the agitated melt so that it is well distributed.

  Yet another method is: a) mixing the magnesium or magnesium-based hydrogen storage alloy powder and the hydrogen desorption catalyst powder; b) the hydrogen desorption catalyst powder particles are at least the magnesium or magnesium-based hydrogen. Mechanically alloying the mixture by an attritor so as to be embedded in the surface of the powder particles of the storage alloy. Preferably heptane and carbon powder are used as grinding aids during mechanical alloying of the mixture.

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

  By combining the above techniques, the catalyst can be dispersed in multiple ways. Bulk or granular magnesium or magnesium-based hydrogen storage alloy a) forms a melt of the magnesium or magnesium-based hydrogen storage alloy, and b) quenches the magnesium or magnesium-based hydrogen storage alloy by bulk quenching. Can be generated. Useful bulk quenching methods include melt spinning, centrifugal spraying, gas spraying, or water spraying.

  We have found that Mg and Mg-based alloys with very low solubility in Mg and Mg-based alloys prevent the growth of Mg or Mg-based crystallites in the alloy, such Mg materials Has been found to catalyze the desorption of hydrogen from water. Accordingly, the present invention provides a magnesium-based hydrogen storage material, wherein the hydrogen storage material is catalyzed by the elimination of hydrogen by iron and / or other elements that are substantially insoluble in the magnesium-based hydrogen storage material. provide. This insoluble catalytic material is composed of 1) an independent dispersion region of the catalytic material in the hydrogen storage material bulk, 2) an independent dispersion region on the particle surface of the hydrogen storage material, and 3) on the surface of the bulk or particulate hydrogen storage material. In the form of continuous or semi-continuous layers of the catalytic material, or 4) combinations thereof. The catalytic material can be added during the alloying process by a special quenching method or by a mechanical alloying method. The catalytic material can also be applied to the surface of the magnesium-based alloy by a process such as thermal evaporation, magnetic sputtering, or by electrolytic or electroless plating.

  Elements with little solid phase solubility in Mg can be used as particle growth inhibitors / desorption catalysts. Specific candidates include Fe (having a solubility of 0.00043 atomic%), Rb (having a solubility of <0.05 atomic%), Nb, Ti, V, and U. In addition, using an element with limited solid-phase solubility in magnesium as part of the intermetallic compound with the elements listed above to form a substance that inhibits crystallite growth at the grain boundary Can do. Candidates include Mn (solubility = 0.99 atomic% in Mg) and Zr (solubility = 1.042 atomic% in Mg).

An agate mortar made of pure metal powder of magnesium (99.8%, -325 mesh), aluminum (99.5%, -325 mesh), iron (99.9 +%, 10 microns) and other trace components -Mix with pestle. Ten different compositions were produced and their composition in weight percent is listed in Table 1. The mixed powder was compressed into 1 cm diameter and 1 cm long pellets using a hard steel die. The compressed pellet was placed in a quartz tube and sintered under vacuum at a temperature of 500 ° C. or higher for 22 hours.

FIG. 1 is a scanning electron micrograph (SEM) taken in backscatter mode of a MM-1 sample sintered / annealed at 500 ° C. This SEM shows the phase separation of Fe and Al ₅ Fe ₂ intermetallics embedded in the main matrix of Mg. Fe and Fe rich phases are approximately a few microns in diameter and the interphase distance is about 10-20 microns. FIG. 2 is an X-ray diffraction pattern of this sample, which was recorded with a Rigaku Mini Flex. This clearly shows the coexistence of Fe and FeAl with the main phase of Mg.

  FIG. 3 is a plot of the pressure-concentration isothermal (PCT) curve of the same material measured at 240 ° C. As can be seen, a very flat plateau pressure was found at about 1800 torr. All absorption / desorption is reversible and the maximum hydrogen capacity is 5 wt%. FIG. 4 plots the percent hydrogen absorption versus time (ie, absorption rate) for the MM-1 alloy at various temperatures. As shown in FIG. 4, the absorption reaction rate improves as the temperature increases. As can be seen, if the absorption temperature is too high, the maximum storage capacity is reduced (see example at 270 ° C.). It can therefore be seen that finding an optimized absorption temperature is a balance between reaction rate and storage capacity. For the MM-1 material, an absorption temperature of about 240 ° C. was found to be most optimal. At a maximum hydrogen supply pressure of 120-150 PSI, over 90% of the hydrogen was absorbed within 2 hours. At higher hydrogen feed pressures, the absorption process time is further reduced. FIG. 5 plots the percent of hydrogen desorbed from MM-1 versus time (ie, desorption rate) at 240 ° C. At this temperature, 90% of the hydrogen was released within 1 hour.

  Another MM-1 material was produced by varying the sintering / annealing temperature by the process described in Example 1. FIG. 6 plots the PCT curves of samples sintered / annealed at 570 ° C. and 600 ° C., respectively. The PCT of the material sintered / annealed at 570 ° C. is slightly displaced from the material of Example 1 (sintered / annealed at 500 ° C.) whereas it is sintered / annealed at 600 ° C. The resulting material provides a broad plateau at slightly higher pressure.

  MM-1 mechanically alloyed (MA) powder was purified from pure elemental magnesium (99.8%, -325 mesh), aluminum (99.5%, -325 mesh), and iron (99.9+). %, 10 microns). The pulverization was performed in a grinder equipped with chrome steel crushing balls. The mechanical alloying process was performed under argon atmosphere while adding 1% graphite and heptane to avoid cake formation on the grinder wall of the material. A typical grinding time is 2 hours. FIG. 7 is a SEM backscattering micrograph of this sample. This figure shows significant phase separation within this material. Region 1 (the bright contrast on the photo) is filled with Fe and Al powder, whereas region 2 (the central dark region) is all magnesium. The XRD plot of this sample, FIG. 8, does not show any signs of any amorphous intermetallic product formed by this process. After MA-MM-1 powder was pressed onto an extended nickel metal substrate, both sides were coated with 100 Å of iron as a surface catalyst.

  FIG. 9 is a plot of the MA-MM-1 PCT curve measured at 240 ° C. The pressure plateau is higher than the sintered MM-1 due to the variation in the distance between the Mg storage phase and the Fe catalyst phase and exhibits a varying reaction rate spectrum. The maximum hydrogen storage capacity increased from 5.0 to 5.7% and the hydrogen was completely desorbed at 240 ° C. FIG. 10 plots the PCT desorption curves of the MA-MM-1 sample at 240 ° C., 210 ° C., 180 ° C., and 150 ° C. The plateau pressure increases with temperature. This phenomenon is expected from thermal equilibrium considerations. However, the maximum storage capacity decreases with decreasing temperature. This feature is not consistent with the thermal equilibrium model. This anomaly is believed to be due to the effect of temperature on the absorption reaction rate. That is, this PCT analysis was performed within a specific time constraint, and therefore it may have underestimated the hydrogen storage capacity at low temperatures. If it was possible to spend more time to achieve equilibrium, a maximum capacity greater than those measured at these lower temperatures may have been achieved.

  A feedstock having the design composition of MM-1 was placed in an air-operated induction furnace with the addition of a flux to isolate the surface from the atmosphere and prevent excessive evaporation of magnesium from the metal liquid. Additional argon was fed into the crucible as an isolation blanket to prevent molten metal oxidation. After all the ingredients were melted in the crucible, the melt was poured into a mold and cooled gradually to room temperature. When the resulting ingot components were examined by inductively coupled plasma (TCP) analysis, no traces of iron were detected. From this comparative example, it can be seen that conventional induction melting technology cannot incorporate iron into the Mg bulk.

  The Mg—Al ingot from above was placed in the bottom injection melt spinning machine. After raising the temperature to above the melting point, the liquid was poured onto a water-cooled copper wheel to form a long ribbon. FIG. 11 is a SEM backscattering micrograph of the ribbon cross section, which shows a very uniform Mg—Al alloy. The ribbon was then cut into small pieces and placed in a grinder for the same MA process as described in Example 3. The ground powder was then pressed onto a Ni-extended metal substrate and coated on both sides with 100 angstroms of Fe.

  This MS + MA-MM-1 shows good hydrogen desorption kinetics at a relatively low temperature. FIG. 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 detachment plateau at 250 Torr is very noteworthy. FIG. 13 compares the maximum reversible hydrogen storage capacity at various temperatures for three different processes (ie, sintering, MA only, MS + MA). The MS + MA process results in the lowest desorption initiation temperature (90 ° C.), but the maximum reversible capacity is also the smallest due to the non-uniform distribution of the Fe phase. The MA only sample shows the onset at the highest desorption temperature (150 ° C.), but the reversible storage capacity is the highest.

  A feedstock with a standard composition of MM-1 was placed in an air-operated induction furnace with a flux added to isolate the molten surface from the atmosphere and prevent excessive magnesium evaporation from the liquid metal. Additional argon was supplied to the crucible as an isolation blanket to prevent metal oxidation. The molten alloy was manually agitated to uniformly suspend the immiscible FeAl and Fe phases in the liquid. This liquid was decanted into a water-cooled quench mold with an argon-protected ladle, and Fe and FeAl phases were incorporated into the final product. FIG. 14 is a SEM micrograph of the cross section of the ingot thus produced, which shows a uniform distribution of FeAl and Fe secondary phases in the Mg host matrix. This Fe inclusion is about 1 micron in size. ICP analysis confirmed the presence of Fe and Al in the ingot. Appropriate stirring in liquids, for example secondary stirring coils, inert gas ventilation, other bulk quenching methods using rotating crucibles, eg melt spinning, centrifugal spraying, gas spraying, water spraying are similar Results can be achieved. FIG. 15 is a schematic view of the microstructure of the hydrogen storage powder material produced by various processing methods of the present invention. All methods make it possible to produce a reversible hydrogen storage material at a temperature substantially lower than that of the prior art.

  The drawings, discussion, descriptions, and examples herein are merely illustrative of specific embodiments of the invention and are not intended to limit its implementation. It is the following claims, including all equivalents, that define the scope of the invention.

Scanning electron micrograph (SEM) taken in backscatter mode of a hydrogen storage material of the present invention made from pure metal powder that was compressed and sintered under vacuum at a temperature above 500 ° C. for 22 hours. X-ray diffraction pattern of the material of FIG. 1 is a pressure-concentration isotherm (PCT) plot of the material of FIG. 1 measured at 240 ° C. FIG. The percent hydrogen absorption versus time (ie, absorption rate) for the material of FIG. 1 is plotted at various temperatures. The percent hydrogen desorbed versus time (ie, desorption rate) for the material of FIG. 1 is plotted at 240 ° C. 1 plots the PCT curve of a sample having the same composition as that of FIG. 1, but sintered / annealed at 570 and 600 ° C., respectively. FIG. 2 is a SEM backscatter photomicrograph of another material according to the present invention having the same composition as the material of FIG. 1 but formed by mechanical alloying. XRD plot of the material of FIG. Plot of the PCT curve of the material of FIG. 7 measured at 240 ° C. The PCT absorption curves for the material of FIG. 7 are plotted at 240 ° C., 210 ° C., 180 ° C., and 150 ° C. 2 is a SEM backscatter photomicrograph of a cross-section of a very uniform Mg-Al alloy melt-spun ribbon used in the manufacture of the material according to the invention. FIG. 3 shows a PCT plot at 150 ° C. of a hydrogen storage material according to the present invention, which is mechanically alloyed, pressed flat on an extended nickel substrate, and 100 angstroms of iron on both sides. Manufactured using the coated material of FIG. Comparative plot of maximum reversible hydrogen storage capacity of the materials of FIGS. 1, 7 and 12 at various temperatures. SEM micrograph of a cross-section of an ingot produced by induction melting and casting the component metal powder necessary for the production of the composition of the material of FIG. 1 while continuously agitating the melt and suspending the insoluble material. . The schematic diagram of the microstructure of the hydrogen storage powder material manufactured by the various processing methods of this invention.

Claims (22)

Magnesium or magnesium-based hydrogen storage alloy,
A hydrogen desorption catalyst;
A magnesium-based hydrogen storage material containing, wherein the hydrogen desorption catalyst is insoluble in the magnesium-based hydrogen storage alloy,
1) Independent dispersion region of the catalytic substance in the bulk of the magnesium or magnesium-based hydrogen storage alloy,
2) An independent dispersion region on the particle surface of the 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 in bulk or particulate form, or 4) combinations thereof,
Hydrogen storage material in the form of   The magnesium-based hydrogen storage material of claim 1, wherein the magnesium-based hydrogen storage alloy comprises at least 80 atomic percent magnesium.   The magnesium-based hydrogen storage material of claim 2, wherein the magnesium-based hydrogen storage alloy further comprises aluminum.   The magnesium-based hydrogen storage material of claim 1, wherein the hydrogen desorption catalyst comprises iron.   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; The magnesium-based hydrogen storage material according to claim 4.   The magnesium-based hydrogen storage material of claim 1, wherein the hydrogen desorption catalyst comprises an independent dispersion region of catalytic material in the bulk of the magnesium or magnesium-based hydrogen storage alloy. a) mixing the magnesium or magnesium-based hydrogen storage alloy powder and the hydrogen desorption catalyst powder;
b) compressing the mixed powder into a compact body;
c) sintering / annealing the tight body at a temperature of 450 ° C. to 600 ° C .;
The magnesium-based hydrogen storage material of claim 6 formed by:   The magnesium-based hydrogen storage material of claim 7, wherein the sintering / annealing is performed for at least 10 hours. a) forming a melt of the magnesium or magnesium-based hydrogen storage alloy powder and the hydrogen desorption catalyst powder in a protective atmosphere;
b) stirring the melt to ensure suspension of the insoluble powder of the hydrogen desorption catalyst in molten magnesium or a magnesium-based hydrogen storage alloy;
c) quenching the stirred melt so that the suspended insoluble powder of the hydrogen desorption catalyst is well distributed within the solid magnesium or magnesium-based hydrogen storage alloy;
The magnesium-based hydrogen storage material of claim 6 formed by:   The magnesium-based hydrogen storage material of claim 1, wherein the hydrogen desorption catalyst comprises an independent dispersed region on a particle surface of the magnesium or magnesium-based hydrogen storage alloy. a) mixing the magnesium or magnesium-based hydrogen storage alloy powder and the hydrogen desorption catalyst powder;
b) mechanically alloying the mixture in a grinder so that the powder particles of the hydrogen desorption catalyst are embedded in at least the surface of the powder particles of the magnesium or magnesium-based hydrogen storage alloy;
The magnesium-based hydrogen storage material of claim 10 formed by:   11. The magnesium-based hydrogen storage material according to claim 10, wherein heptane and carbon powder are used as a crushing aid during mechanical alloying of the mixture.   The magnesium-based hydrogen storage material of claim 1, wherein the hydrogen desorption catalyst comprises a continuous or semi-continuous layer of catalytic material on the surface of the magnesium or magnesium-based hydrogen storage alloy in bulk or particulate form. a) producing bulk or particulate magnesium or a magnesium-based hydrogen storage alloy;
b) depositing a continuous or semi-continuous layer of catalytic material on the surface of said bulk or particulate magnesium or magnesium-based hydrogen storage alloy by vapor deposition, electrolysis coating or electroless coating;
The magnesium-based hydrogen storage material of claim 13 formed by:   15. The magnesium based hydrogen storage of claim 14, wherein depositing a continuous or semi-continuous layer of catalytic material on the bulk or particulate magnesium or magnesium based hydrogen storage alloy surface comprises evaporation of the catalytic material. material.   14. The magnesium-based hydrogen storage material of claim 13, wherein the continuous or semi-continuous layer of catalytic material is about 100 angstroms thick.   A hydrogen desorption catalyst in which the step of producing the bulk or particulate magnesium or magnesium-based hydrogen storage alloy is arranged in a state of independent dispersion in the bulk or particulate magnesium or magnesium-based hydrogen storage alloy 15. The magnesium-based hydrogen storage material of claim 14, comprising providing bulk or particulate magnesium or a magnesium-based hydrogen storage alloy having: The step of producing the bulk or particulate magnesium or magnesium-based hydrogen storage alloy,
a) mixing the magnesium or magnesium-based hydrogen storage alloy powder and the hydrogen desorption catalyst powder;
b) Compressing the mixed powder into a compact body,
c) sintering / annealing the tight body at a temperature of 450 ° C. to 600 ° C .;
The magnesium-based hydrogen storage material of claim 17, comprising:   The magnesium-based hydrogen storage material of claim 18, wherein the sintering / annealing is performed for at least 10 hours. Producing the bulk or particulate magnesium or magnesium-based hydrogen storage alloy,
a) forming a melt of the magnesium or magnesium-based hydrogen storage alloy powder and the hydrogen desorption catalyst powder in a protective atmosphere;
b) stirring the melt to ensure suspension of the insoluble powder of the hydrogen desorption catalyst in molten magnesium or a magnesium-based hydrogen storage alloy;
c) quenching the melt so that the suspended insoluble powder of the hydrogen desorption catalyst is well distributed within the solid magnesium or magnesium-based hydrogen storage alloy;
The magnesium-based hydrogen storage material of claim 17, comprising: Producing the bulk or particulate magnesium or magnesium-based hydrogen storage alloy,
a) forming a melt of said magnesium or magnesium-based hydrogen storage alloy;
b) quenching the magnesium or magnesium-based hydrogen storage alloy by bulk quenching;
The magnesium-based hydrogen storage material of claim 14, comprising:   The magnesium-based hydrogen storage material of claim 21, wherein the bulk quench method comprises a melt spinning method, a centrifugal spray method, a gas spray method, or a water spray method.

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