WO2006036742A2 - Metal alanates doped with oxygen - Google Patents

Metal alanates doped with oxygen Download PDF

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Publication number
WO2006036742A2
WO2006036742A2 PCT/US2005/033997 US2005033997W WO2006036742A2 WO 2006036742 A2 WO2006036742 A2 WO 2006036742A2 US 2005033997 W US2005033997 W US 2005033997W WO 2006036742 A2 WO2006036742 A2 WO 2006036742A2
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Prior art keywords
metal
oxygen
alanate
doped
recited
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PCT/US2005/033997
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French (fr)
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WO2006036742A3 (en
Inventor
Xia Tang
Donald L. Anton
Susanne M. Opalka
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UTC Power Corp
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UTC Power Corp
UTC Fuel Cells LLC
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Priority to JP2007533628A priority Critical patent/JP4633799B2/en
Priority to DE112005002381T priority patent/DE112005002381T5/en
Publication of WO2006036742A2 publication Critical patent/WO2006036742A2/en
Publication of WO2006036742A3 publication Critical patent/WO2006036742A3/en
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04201—Reactant storage and supply, e.g. means for feeding, pipes
    • H01M8/04216—Reactant storage and supply, e.g. means for feeding, pipes characterised by the choice for a specific material, e.g. carbon, hydride, absorbent
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof
    • C01B6/24—Hydrides containing at least two metals; Addition complexes thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen; Reversible storage of hydrogen
    • C01B3/0005—Reversible storage of hydrogen, e.g. by hydrogen getters or electrodes
    • C01B3/001—Reversible storage of hydrogen, e.g. by hydrogen getters or electrodes characterised by the uptaking media; Treatment thereof
    • C01B3/0018—Inorganic elements or compounds, e.g. oxides, nitrides, borohydrides or zeolites; Solutions thereof
    • C01B3/0031—Intermetallic compounds; Metal alloys
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof
    • C01B6/24—Hydrides containing at least two metals; Addition complexes thereof
    • C01B6/243—Hydrides containing at least two metals; Addition complexes thereof containing only hydrogen, aluminium and alkali metals, e.g. Li(AlH4)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof
    • C01B6/24—Hydrides containing at least two metals; Addition complexes thereof
    • C01B6/246—Hydrides containing at least two metals; Addition complexes thereof also containing non-metals other than hydrogen
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2250/00—Fuel cells for particular applications; Specific features of fuel cell system
    • H01M2250/20—Fuel cells in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/065—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants by dissolution of metals or alloys; by dehydriding metallic substances
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/32—Hydrogen storage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02T90/40—Application of hydrogen technology to transportation, e.g. using fuel cells

Definitions

  • Metal alanates such as NaAlH 4
  • a metal alanate stores and releases hydrogen, and can be replenished with hydrogen at moderate pressures and -temperatures.
  • dehydrogenation i.e., liberation of hydrogen
  • hydrogen is recharged back into the metal alanate.
  • Fuel cell devices for example, can utilize metal alanates because of these relatively temperate dehydrogenation and hydrogenation conditions.
  • thermodynamic catalysts In an effort to increase the hydrogen storage capacity of conventional metal alanates, it has been proposed to add dopant amounts of certain transition metals as thermodynamic catalysts. Typically, doping with approximately 2-6 mol% of the transition metal, such as Sc, Ti, or Zr, significantly increases the hydrogen absorption and desorption kinetics.
  • a drawback of using conventional transition metal dopants is the diminishing, or negative, effectiveness of the dopants in amounts over 2mol%.
  • the hydrogen absorption of NaAlH 4 decreases substantially when the amount of a Sc dopant increases from 2.0mol% to 3.3mol%.
  • the limit of effectiveness of a Sc dopant is 2.0mol%.
  • Ti has been effectively used as a catalyst in NaAlH 4 up to 6mol% concentrations. These higher levels of dopant come at the cost of increased halide content, which forms NaCl or NaF thus reducing overall capacity. Increasing catalyst content over 4mol% is thus undesirable.
  • a metal alanate material that provides increased hydrogen storage capacity beyond that which is available from the limited effectiveness of conventional dopants is needed.
  • this invention is a metal alanate material used for reversible storage of hydrogen as in fuel cell applications.
  • the metal alanate base material is one of an alkali metal alanate or a mixed alkali metal-alkaline earth metal alanate.
  • the base metal alanate material is doped with approximately 0.5%-30% oxygen (on a molecular basis) to thereby enhance the hydrogen storage kinetics and capacity of the material.
  • the source of dopant oxygen is a solid oxide.
  • the solid oxide is selected from a group of unstable solid oxides, those with a - ⁇ G f ° ⁇ 200 Kcal/mole, including Cu 2 O, NiO, PdO, SeO 2 , ZnO, for example.
  • the solid oxide is doped into the metal alanate using a known ball-milling technique.
  • the oxygen may be introduced to the metal alanate by a gas mixture including oxygen gas and an inert gas.
  • a metal alanate doped with oxygen allows the dopants, such as Sc, to be used in amounts that exceed the previous limitation of effectiveness of 2mol%.
  • Metal alanates doped with oxygen provide an improved reversible hydrogen storage material and exhibit favorable kinetic and thermodynamic characteristics required for use in fuel cell devices, for example.
  • Figure 1 is a general schematic view of an automobile having a fuel cell device with a hydrogen storage portion designed according to this invention.
  • Figure 2 graphically shows example hydro genati on results using an example metal alanate material designed according to the invention.
  • FIG. 1 schematically shows an automobile 10 utilizing a fuel cell device 12 for power.
  • the fuel cell device 12 requires hydrogen, and therefore an on-board source of storing the hydrogen.
  • a hydrogen storage portion 14 of the fuel cell device 12 includes a metal alanate material that is doped with oxygen.
  • the base material of the metal alanate material can be an alkali metal alanate, a mixed alkali metal-alkaline earth metal alanate or a transition metal alanate.
  • the alkali metal alanate in one example preferably is NaAlH 4 and the mixed alkali metal-alkaline earth metal alanate preferably is described by the formula: where M 1 is an alkali metal; M 2 is an alkaline earth metal; and 0 ⁇ x ⁇ 1.
  • a transition metal alanate could be used such as Tm +1 (AlH 4 )I where Tm is a transition metal having a valence state, i.
  • a mixed Alkaline metal, alkaline earth metal and transition metal such as
  • M 1 is an alkali metal
  • M 2 is an alkaline earth metal
  • Tm is a transition metal having a valence state
  • i, x + y 1, and O ⁇ x, y ⁇ l.
  • base metal alanate materials may be doped with approximately 2mol% of certain transition metals to enhance the hydrogenation thermodynamics.
  • a dopant such as Sc
  • Sc can be added to a base metal alanate material via any number of methods known in the art. Sc in particular has a superior catalytic effect compared to some other common dopants. For example, the rehydrogenation rate of NaAlH 4 using a Ti catalyst added in the form of TiCl 2 yields a rehydrogenation rate of less than 0.36wt%/hr under conditions of 100 0 C and 60 bar.
  • metal alanate material approximately 0.5mol%-30mol% of dopant oxygen lowers the equilibrium pressure associated with the Sc dopant.
  • the dopant oxygen lowers the equilibrium pressure and allows a Sc dopant to be added at levels exceeding the previously effective limits (i.e., 2mol%).
  • the Sc dopant may be added at levels up to approximately 25mol%.
  • the dopant oxygen counteracts the increase in equilibrium pressure associated with the increased Sc dopant (i.e., an amount over 2mol%) and yields favorable hydrogenation characteristics.
  • the hydrogen storage capacity Of NaAlH 4 with a Sc dopant added in the form of ScCl 3 at 3.3mol% is approximately 1.50%.
  • the storage capacity of NaAlH 4 with the same amount of Sc dopant added in the form of ScCl 3 and dopant oxygen added in the form of Na 2 O, however, is 4.50- 5.00%. This is shown by curve 24.
  • Xhe dopant oxygen counteracted the increased equilibrium pressure associated with the Sc catalyst. Similar results follow for catalysts other than Sc. Improved results are available even when using the previously believed optimum Sc dopant amount.
  • the curve 26 shows that adding 0.67mol% Sc 2 O 3 in addition to 2mol% ScCl 3 increases the absorbed hydrogen to more than 4.5wt%, compared to just over 4.0wt% absorbed hydrogen for 2mol% ScCl 3 shown by curve 22. In this example an additional 0.5wt% absorption becomes possible because of the added oxygen dopant.
  • Several different known methods may be used to dope a base metal alanate material with oxygen.
  • high energy ball-milling is one preferred method, using solid oxides or hydroxides as the oxygen source.
  • the preferred solid oxide oxygen sources include an unstable oxide, such as those having - ⁇ G° f ⁇ 200 kcal/mol.
  • an unstable oxide such as those having - ⁇ G° f ⁇ 200 kcal/mol.
  • Example suitable nitrates include AgNO 3 , CdNO 3 , Co(NO 3 ) 2 , CsNO 3 , Cu(NO 3 ) 2 , Fe(NO 3 ) 2 , KNO 3 , LiNO 3 , NaNO 3 , NH 4 NO 3 , Ni(NO 3 ) 2 , Pb(NO 3 ) 2 , RbNO 3 , and Zn (NOs) 2 .
  • Example suitable carbonates include CdCO 3 , C0C0 3 , CuCO 3 , FeCO 3 , PbCO 3 , MnCO 3 , Na 2 CO 3 and ZnCO 3 .
  • Another means of incorporating oxygen can be through hydroxides.
  • Example hydroxides include Cd(OH) 2 , CsOH, Cu(OH) 2 , KOH, LiOH, Mn(OH) 3 , N 2 OH, Ni(OH) 2 , Pb(OH) 2 , Pd(OH) 2 , Pt(OH) 2 , RbOH, Sn(OH) 2 , Tl(OH) 3 and Zn(OH) 2 .
  • an unstable oxide or hydroxide is ball-milled with a base metal alanate material, the oxide compound disassociates and the oxygen dopes into the metal alanate base material or is otherwise incorporated into the compound.
  • a base metal alanate material the oxide compound disassociates and the oxygen dopes into the metal alanate base material or is otherwise incorporated into the compound.
  • One skilled in the art who has the benefit of this description will recognize additional suitable unstable solid oxides, mixed oxides or hydroxides.
  • Oxygen may be introduced into a base metal alanate material through partial oxidation using oxygen gas in mixture with a non-reactive gas such as N 2 or Ar.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • General Chemical & Material Sciences (AREA)
  • Sustainable Development (AREA)
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  • Combustion & Propulsion (AREA)
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Abstract

A metal alanate material useful for reversible hydrogen storage as in fuel cell applications includes a metal alanate material that is doped with oxygen. In discussed examples, the metal alanate material is one of an alkali metal alanate or mixed alkali metal-alkaline earth metal alanate. In some examples, the oxygen is doped into the metal alanate from an unstable solid oxide having -?G<sub

Description

METAL ALANATES DOPED WITH OXYGEN
BACKGROUND OF THE INVENTION
This invention relates to reversible hydrogen storage material. More particularly, this invention relates to a metal alanate material that is doped with oxygen, thereby allowing increased hydrogen absorption kinetics and storage capacity compared to previously known doped metal alanate materials.
Metal alanates, such as NaAlH4, are generally known as reversible hydrogen storage materials. A metal alanate stores and releases hydrogen, and can be replenished with hydrogen at moderate pressures and -temperatures. At approximately 8O0C dehydrogenation (i.e., liberation of hydrogen) of the metal alanate is thermodynamically favorable. In a reverse rehydrogenation reaction at 100°-120°C and 60-100 bar, hydrogen is recharged back into the metal alanate. Fuel cell devices, for example, can utilize metal alanates because of these relatively temperate dehydrogenation and hydrogenation conditions.
In applications such as a fuel cell device, greater volumetric hydrogen storage capacity is desirable. In an effort to increase the hydrogen storage capacity of conventional metal alanates, it has been proposed to add dopant amounts of certain transition metals as thermodynamic catalysts. Typically, doping with approximately 2-6 mol% of the transition metal, such as Sc, Ti, or Zr, significantly increases the hydrogen absorption and desorption kinetics.
A drawback of using conventional transition metal dopants is the diminishing, or negative, effectiveness of the dopants in amounts over 2mol%. For instance, the hydrogen absorption of NaAlH4 decreases substantially when the amount of a Sc dopant increases from 2.0mol% to 3.3mol%. The limit of effectiveness of a Sc dopant is 2.0mol%. Ti has been effectively used as a catalyst in NaAlH4 up to 6mol% concentrations. These higher levels of dopant come at the cost of increased halide content, which forms NaCl or NaF thus reducing overall capacity. Increasing catalyst content over 4mol% is thus undesirable. A metal alanate material that provides increased hydrogen storage capacity beyond that which is available from the limited effectiveness of conventional dopants is needed. Mechanical milling of NaAlH4 with some oxides such as Al2O3 and CeO2 have been noted in the literature with only slight enhancement of kinetics. Utilizing oxides with -ΔGf°>200 Kcal/mole such as Al2O3 and CeO2 does not lead to incorporation of the oxygen into the system and thus limited kinetic activity.
SUMMARY OF THE INVENTION
In general terms, this invention is a metal alanate material used for reversible storage of hydrogen as in fuel cell applications.
In one example, the metal alanate base material is one of an alkali metal alanate or a mixed alkali metal-alkaline earth metal alanate. The base metal alanate material is doped with approximately 0.5%-30% oxygen (on a molecular basis) to thereby enhance the hydrogen storage kinetics and capacity of the material.
In one example, the source of dopant oxygen is a solid oxide. The solid oxide is selected from a group of unstable solid oxides, those with a -ΔGf° <200 Kcal/mole, including Cu2O, NiO, PdO, SeO2, ZnO, for example. In one example, the solid oxide is doped into the metal alanate using a known ball-milling technique. Alternatively, the oxygen may be introduced to the metal alanate by a gas mixture including oxygen gas and an inert gas.
A metal alanate doped with oxygen allows the dopants, such as Sc, to be used in amounts that exceed the previous limitation of effectiveness of 2mol%. Metal alanates doped with oxygen provide an improved reversible hydrogen storage material and exhibit favorable kinetic and thermodynamic characteristics required for use in fuel cell devices, for example.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a general schematic view of an automobile having a fuel cell device with a hydrogen storage portion designed according to this invention; and
Figure 2 graphically shows example hydro genati on results using an example metal alanate material designed according to the invention. DETAILED DESCRIPTION OF THE PREFFERRED EMBODIMENT
Figure 1 schematically shows an automobile 10 utilizing a fuel cell device 12 for power. In generating power, the fuel cell device 12 requires hydrogen, and therefore an on-board source of storing the hydrogen. A hydrogen storage portion 14 of the fuel cell device 12 includes a metal alanate material that is doped with oxygen.
The base material of the metal alanate material can be an alkali metal alanate, a mixed alkali metal-alkaline earth metal alanate or a transition metal alanate. The alkali metal alanate in one example preferably is NaAlH4 and the mixed alkali metal-alkaline earth metal alanate preferably is described by the formula:
Figure imgf000005_0001
where M1 is an alkali metal; M2 is an alkaline earth metal; and 0 < x < 1. Alternatively, a transition metal alanate could be used such as Tm+1 (AlH4)I where Tm is a transition metal having a valence state, i. Alternatively a mixed Alkaline metal, alkaline earth metal and transition metal such as
Mx1 My2 TmVx-y) (AlH4)x+2y+i-ix-iy where M1 is an alkali metal, M2 is an alkaline earth metal, Tm is a transition metal having a valence state, i, x + y = 1, and O≤x, y≤l. One skilled in the art who has the benefit of this description would recognize additional suitable base metal alanate materials that would be useful for making a material according to this invention.
As is known in the art, base metal alanate materials may be doped with approximately 2mol% of certain transition metals to enhance the hydrogenation thermodynamics. A dopant, such as Sc, can be added to a base metal alanate material via any number of methods known in the art. Sc in particular has a superior catalytic effect compared to some other common dopants. For example, the rehydrogenation rate of NaAlH4 using a Ti catalyst added in the form of TiCl2 yields a rehydrogenation rate of less than 0.36wt%/hr under conditions of 1000C and 60 bar. Under the same conditions, NaAlH4 using Sc added in the form of ScCl3 yields a rehydrogenation rate of 1.03wt%/hr. Referring to Figure 2, the addition of Sc in amounts exceeding 2mol% substantially reduces the hydrogen storage capacity of the metal alanate material. Under hydrogenation conditions of 1000C and 60-68 atm ultra high purity, UHP, hydrogen, NaAlH4 doped with 3.3rnol% Sc added in the form of ScCl3 shows a total hydrogen storage capacity of approximately 1.5wt% after 10 hours. This is shown by the curve 20. Under the same conditions, NaAlH4 doped with 2.0mol% Sc added in the form of ScCl3 yields a total hydrogen storage capacity of 4.00-4.50wt% after 10 hours. This is shown by the curve 22. Accordingly, any additional Sc catalyst over 2.0mol% has a negative effect on hydrogen storage capacity. The decreased hydrogen storage capacity in metal alanates with Sc levels exceeding 2mol% is more than expected due to the weight of the catalyst itself. For a fixed volume of metal alanate, a catalyst displaces a portion of the hydrogen storing base metal alanate material. Consequently, the use of a catalyst involves competing interests; the beneficial catalytic effect versus reduced hydrogen capacity from displaced base metal alanate. One skilled in the art can calculate the expected loss in hydrogen storage capacity due to the catalyst displacing the base metal alanate.
When increasing the amount of Sc catalyst from 2.0mol% to 3.3mol%, there is an expected loss of hydrogen storage capacity due to the catalyst displacing the base metal alanate. The actual loss of hydrogen storage capacity is greater than the expected loss. Therefore, the Sc must also be acting as a thermodynamic inhibitor to the base metal alanate. This is mainly due to an increase in equilibrium pressure from the "excess" Sc dopant.
With this invention, increased performance is possible, and the decreasing effectiveness of increased metal dopants is avoided.
In one example metal alanate material, approximately 0.5mol%-30mol% of dopant oxygen lowers the equilibrium pressure associated with the Sc dopant. The dopant oxygen lowers the equilibrium pressure and allows a Sc dopant to be added at levels exceeding the previously effective limits (i.e., 2mol%). In some examples, the Sc dopant may be added at levels up to approximately 25mol%. The dopant oxygen counteracts the increase in equilibrium pressure associated with the increased Sc dopant (i.e., an amount over 2mol%) and yields favorable hydrogenation characteristics.
Referring to curve 20 in Figure 2 for example, the hydrogen storage capacity Of NaAlH4 with a Sc dopant added in the form of ScCl3 at 3.3mol% is approximately 1.50%. The storage capacity of NaAlH4 with the same amount of Sc dopant added in the form of ScCl3 and dopant oxygen added in the form of Na2O, however, is 4.50- 5.00%. This is shown by curve 24. Xhe dopant oxygen counteracted the increased equilibrium pressure associated with the Sc catalyst. Similar results follow for catalysts other than Sc. Improved results are available even when using the previously believed optimum Sc dopant amount. The curve 26 shows that adding 0.67mol% Sc2O3 in addition to 2mol% ScCl3 increases the absorbed hydrogen to more than 4.5wt%, compared to just over 4.0wt% absorbed hydrogen for 2mol% ScCl3 shown by curve 22. In this example an additional 0.5wt% absorption becomes possible because of the added oxygen dopant.
Several different known methods may be used to dope a base metal alanate material with oxygen. In one example high energy ball-milling is one preferred method, using solid oxides or hydroxides as the oxygen source.
The preferred solid oxide oxygen sources include an unstable oxide, such as those having -ΔG°f <200 kcal/mol. For example, BaO2, BeO, Bi2O3, CdO, Cu2O, Au2O3, IrO2, Li2O, Hg2O, NiO, Tl2O, SeO2, ZnO, TeO2, Ag2O, PuO2, PdO, Na2O and ZnO, are effective oxygen sources when ball-milling is the selected doping technique. Example suitable nitrates include AgNO3, CdNO3, Co(NO3)2, CsNO3, Cu(NO3)2, Fe(NO3)2, KNO3, LiNO3, NaNO3, NH4NO3, Ni(NO3)2, Pb(NO3)2, RbNO3, and Zn (NOs)2. Example suitable carbonates include CdCO3, C0C03, CuCO3, FeCO3, PbCO3, MnCO3, Na2CO3 and ZnCO3. Another means of incorporating oxygen can be through hydroxides. Example hydroxides include Cd(OH)2, CsOH, Cu(OH)2, KOH, LiOH, Mn(OH)3, N2OH, Ni(OH)2, Pb(OH)2, Pd(OH)2, Pt(OH)2, RbOH, Sn(OH)2, Tl(OH)3 and Zn(OH)2. When an unstable oxide or hydroxide is ball-milled with a base metal alanate material, the oxide compound disassociates and the oxygen dopes into the metal alanate base material or is otherwise incorporated into the compound. One skilled in the art who has the benefit of this description will recognize additional suitable unstable solid oxides, mixed oxides or hydroxides.
Another method of doping a base material with oxygen is via an oxygen gas mixture. Oxygen may be introduced into a base metal alanate material through partial oxidation using oxygen gas in mixture with a non-reactive gas such as N2 or Ar.
The invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Vaαrious modifications and variations of the given examples are possible in light of trie above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims

1. A composition of matter comprising a metal alanate material doped with oxygen.
2. The composition of matter as recited in claim 1, wherein the metal alanate is NaAlH4.
3. The composition of matter as recited in claim 1, wherein the metal alanate is M1Q-2X)M2 X (AlH4), wherein
M1 is an alkali metal;
M2 is an alkaline metal; and
0 < x < 9.
4. The composition of matter as recited, in claim 1, wherein the metal alanate material is doped with at least one of an unstable metal oxide, a hydroxide, a nitrate or a carbonate.
5. The composition of matter as recited in claim 4, wherein the unstable metal oxide has -ΔGf° <200 Kcal/mole.
6. The composition of matter as recited in claim 1, wherein the oxygen is from an oxygen gas mixture.
7. The composition of matter as recited in claim 1, wherein the metal alanate material is doped with between 0.5mol% and 30mol% oxygen.
8. A fuel cell device comprising: a hydrogen storage portion comprising a metal alanate material doped with oxygen.
9. The fuel cell device as recited in claim 8, wherein the metal alanate material is NaAlH4.
10. The fuel cell device as recited in claim 8, wherein the metal alanate material is M^1-2X)M2 X (AlH4), wherein
M1 is an alkali metal;
M2 is an alkaline metal; and
0 < x < 9.
11. The fuel cell device as recited in claim 8, wherein the metal alanate material is doped with at least one of an unstable metal oxide, a hydroxide, a nitrate or a carbonate.
12. The fuel cell device as recited in claim 11, wherein the unstable metal oxide has -ΔGP° <200 Kcal/mole.
13. The fuel cell device as recited in claim 8, wherein the oxygen source is an oxygen gas mixture.
14. The metal alanate material as recited in claim 8, wherein the metal alanate material is doped with between 0.5mol% and 30rnol% oxygen.
15. A method of making a hydrogen storage material comprising: doping a metal alanate material with oxygen.
16. The method of claim 15, wherein the metal alanate material comprises NaAlH4.
17. The method of claim 15, wherein the metal alanate comprises M!(1-2x)M2χ (AlH4), and wherein
M1 is an alkali metal;
M2 is an alkaline metal; and
0 ≤ x < 9.
18. The method of claim 15, including doping the metal alanate material with at least one of an unstable metal oxide, a hydroxide, a nitrate or a carbonate.
19. The method of claim 18, wherein the unstable metal oxide has -ΔGV200 Kcal/mole.
20. The method of claim 15, including using an oxygen gas mixture.
21. The method of claim 15, including doping the metal alanate material with between 0.5mol% and 30mol% oxygen.
PCT/US2005/033997 2004-09-27 2005-09-27 Metal alanates doped with oxygen Ceased WO2006036742A2 (en)

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US4528176A (en) * 1982-12-15 1985-07-09 Ethyl Corporation Sodium aluminum hydride production
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US6471935B2 (en) * 1998-08-06 2002-10-29 University Of Hawaii Hydrogen storage materials and method of making by dry homogenation
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US7169489B2 (en) * 2002-03-15 2007-01-30 Fuelsell Technologies, Inc. Hydrogen storage, distribution, and recovery system
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