Classifications

• • 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
• • 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
  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0078—Composite solid storage mediums, i.e. coherent or loose mixtures of different solid constituents, chemically or structurally heterogeneous solid masses, coated solids or solids having a chemically modified surface region
• • 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

Definitions

• the present invention relates generally to the field of reversible hydrogen storage. More particularly, the present invention relates to a dry homogenized metal hydrides, in particular aluminum hydride compounds, as a material for reversible hydrogen storage, and a method of making the same.
• LaNiH 5 has been investigated but has not proved satisfactory, due in part to its high cost. Unfortunately, despite decades of extensive effort, especially in the area of metal hydrides, no material has been found which has the combination of a high gravimetric hydrogen density, adequate hydrogen dissociation energetics, and low cost required for commercial vehicular applications.
• the present invention provides novel reversible hydrogen storage materials and methods of making said materials, that are readily prepared from cheap, abundant starting materials.
• the present invention provides a new dry doping method comprising the steps of dry homogenizing metal hydrides by mechanical mixing, such as by crushing or ball milling a powder, of a metal aluminum hydride with a transition metal catalyst.
• the metal aluminum hydride is of the general formulas of: X , A1H 4 , where X, is an alkali metal; X 2 (A1H 4 ) 2 , where X 2 is an alkaline earth metal; X 3 (A1H 4 ) 4 , where X 3 is Ti, Zr or Hf; X 4 A1H 6 , where X 4 is an alkali metal; X 5 (A1H 6 ) 2 , where X 5 is an alkaline earth metal; X ⁇ ⁇ A1H j) ⁇ where X 6 is Ti, Zr or Hf; or any combination of the above hydrides.
• a material for storing and releasing hydrogen comprising a dry homogenized material having transition metal catalytic sites on a metal aluminum hydride compound, or mixtures of metal aluminum hydride compounds.
• the inventors have found that the homogenization method of the present invention of metal aluminum hydrides with transition metal catalysts resulted in a lowering of the dehydriding temperature by as much as 75 °C and markedly improves the cyclable hydrogen capacities.
• Figure 1 shows a comparison of thermal desorption (2 °C/min) of hydrogen from undoped and wet titanium doped NaAlH 4 of the prior art, and one embodiment of the material of the present invention, in this case dry homogenized titanium doped NaAlH 4 .
• Figure 2 depicts thermal programmed desorption (2 °C/min) of hydrogen from samples of dry titanium doped NaAlH4 material of the present invention prepared from 1, 2 and 4 (0.5x, x, and 2x) mol of transition metal catalyst Ti(OBu n ) 4 .
• Figure 3 shows a comparison of thermal programmed desorption (2 ° C/min) of hydrogen from undoped and wet titanium doped NaAlH 4 of the prior art, and one embodiment of the material of the present invention, in this case dry homogenized titanium doped NaAlH 4 , following one dehydrogenation/rehydrogenation cycle.
• Figure 4 illustrates the effect of dehydriding/rehydriding cycles on thermal programmed desorption (2°C min 1 ) of hydrogen from an alternative embodiment of the material of the present invention, in this case NaAlH 4 doped with zirconium.
• Figure 5 shows the effect of dehydriding/rehydriding cycles on thermal programmed desorption (2°C min 1 ) of hydrogen from titanium doped NaAlH 4 , using the homogenization method of the present invention.
• Figure 6 illustrates the thermal programmed desorption (2°C min 1 ) of hydrogen from various doped samples of NaAlH 4 according to the present invention after three cycles of dehydriding/rehydriding.
• the present invention provides novel reversible hydrogen storage materials and methods of making said materials, that are readily prepared from cheap, abundant starting materials.
• the present invention provides a new dry doping method comprising the steps of dry homogenizing metal hydrides by mechanical mixing, such as by crushing or ball milling a powder, of a metal aluminum hydride with a transition metal catalyst.
• the metal aluminum hydride is of the general formulas of: X ,A1H 4 , where X, is an alkali metal; X 2 (A1H 4 ) 2 , where X 2 is an alkaline earth metal; X 3 (A1H 4 ) 4 , where X 3 is Ti, Zr or Hf; X 4 A1H 6 , where X 4 is an alkali metal; X 5 (A1H 0 ) 2 , where X 5 is an alkaline earth metal; X 6 (A1H ⁇ 4 , where X 6 is Ti, Zr or Hf; or any combination of the above hydrides.
• a material for storing and releasing hydrogen is provided, consisting of a dry homogenized
• the hydrogen storage material is used to power a vehicle apparatus, and the novel method further includes the steps of dehydrogenating the dry homogenized hydrogen storage material to release hydrogen, and powering a vehicle apparatus with the released hydrogen.
• the material and method of the present invention are quite different from the prior art (in particular Bogdanovic' s doped material) and exhibit markedly improved, and unexpected, catalytic effects.
• the inventors have found that the homogenization method of the present invention of metal aluminum hydrides with transition metal catalysts results in a lowering of the dehydriding temperature by as much as about 75 °C and markedly improves the cyclable hydrogen capacities.
• the dehydrogenation of certain metal aluminum hydrides are thermodynamically favorable at moderate temperatures. It is known to occur by a multi step process involving the reactions illustrated in equations 1 and 2. While this material has a relatively high percentage of hydrogen, the process exhibits very slow reaction kinetics and is reversible only under severe conditions. An example of severe conditions would be at a pressure of about 175 atmospheres of hydrogen at about 270 °C. In great contrast to the prior art, the dehydrogenation kinetics of NaAlH 4 according to the present invention have been enhanced far beyond those previously achieved upon titanium doping of the host hydride.
• homogenization of NaAlH 4 with approximately 2 mole % of titanium catalyst, in particular Ti (OBu n ) 4 , under an atmosphere of argon produces a novel material that contains only traces of carbon.
• Thermal programmed deso ⁇ tion (TPD) measurements show that the dehydrogenation of this material occurs about 30 °C lower than that previously found for NaAlH 4 doped with titanium through wet chemistry methods. This lowering of the temperature of dehydrogenation represents a significant advance towards enabling the use of the material as a hydrogen storage material for powering vehicles with hydrogen.
• the novel titanium containing material can be completely rehydrided under 150 atm of hydrogen pressure at 170 °C.
• the dehydrogenation kinetics observed for this novel material are undirninished over several dehydriding/hydriding cycles.
• Suitable aluminum hydrides which may be practiced with this method are generally of the formulae: X,A1H 4 , where X, is an alkali metal; X ⁇ AIH ⁇ , where X; is an alkaline earth metal; X, (A1H 4 ) 4 , where X 3 is Ti, Zr or Hf; X 4 A ⁇ H ⁇ ;, where X, is an alkali metal; X 5 (A1H 6 ) 2 , where j is an alkaline earth metal; X 6 (A1H 6 ) 4 , where X 6 is Ti, Zr or Hf; or any combination of the above hydrides.
• suitable aluminum hydrides include, but are not limited to: sodium aluminum hydride (NaAlH 3 ), sodium aluminum hexahydride (Na 3 AlH 6 ), magnesium aluminum hydride (Mg(AlH, ⁇ ), titanium aluminum hydride (Ti(AlH 4 ) 4 ), zirconium aluminum hydride (Zr(AlH 4 ) 4 ), and the like.
• the transition metal catalyst used with the present invention include titanium, zirconium, vanadium, iron, cobalt or nickel.
• transition metal and lanthanide metal complexes which are suitable catalyst precursors include, but are not limited to Ti(OBu) 4 , Zr(OPr) 4 , VO(OPri) 3 , Fe(acac) 2 , Co(acac) 2 , Ni(l,5-cyclooctadiene) 2 , La(acac) 3 , and mixtures thereof, where acac is acetylacetonate and Pri is isopropyl.
• the hydrogen storage material of the present invention is comprised of NaAlH 4 doped by dry homogenation with Ti(OBu n ) .
• the hydrogen storage material of the present invention is comprised of NaAlH 4 doped with Zr(OPr) 4 catalyst by dry homogenation.
• dry homogenation is performed to dope the aluminum hydride with the transition metal catalyst.
• Homogenation is performed by mechanical methods; such as for example by manual grinding in a mortar and pestle, preferably for about 15 minutes; by mechanically blending in a mixer-grinder mill, preferably for a time in the range of about 5 to 10 minutes; or by balling, preferably for a time in the range of about 5 to 20 minutes.
• the homogenation process is considered “dry” because the process takes place in the absence of a solvent or any aqueous medium.
• the homogenation process is performed in an inert atmosphere, such as argon, and the like.
• the amount of transition metal catalyst used in the dry homogenation process of the present invention is not particularly limited, and is generally selected as that amount useful for providing the desired catalytic activity.
• at least 0.2 mol % of the titanium precursor is used in the doping of the hydride.
• the maximum catalytic effect is observed at about 2.0 mol % of the titanium precursor, and the catalytic effect is not improved by doping with greater than 2.0 mol % of the titanium precursor.
• An illustrated preferred range when doping the hydride with a titanium catalyst is in the range of about 0.5 to about 1 mol % Ti catalyst to aluminum hydride.
• An illustrated preferred range when doping the hydride with a zirconium catalyst is in the range of about 0.5 to about 1 mol % Zr catalyst to aluminum hydride.
• NaAlH 4 is doped with Ti (OBun) in an inert atmosphere according to the method of the present invention to produce an inventive material for storing and releasing hydrogen.
• the novel titanium containing (dry doped) materials were prepared by adding prescribed amounts of Ti (OBu ⁇ ) 4 to freshly recrystallized NaAlH 4 under an atmosphere of argon. The originally colorless mixtures were homogenized using a mortar and pestle until they became red-violet. This color change suggests that at least some of the Ti4+ was reduced to Ti3+. The resulting paste was visually very distinct from the brown powders obtained through Bogdanovic's procedure for producing titanium containing (wet doped) material.
• the inventors have investigated the dehydriding/rehydriding behavior of NaAlH 4 in which a zirconium catalyst was introduced according to the dry homogenation doping method of the present invention. While zirconium was found to enhance the dehydriding kinetics of NaAlH 4 , the catalytic action is seen to be different than that of titanium. Furthermore, the inventors have found that the differing catalytic effects of titanium and zirconium can be carried out in concert. TPD measurements were made on the following samples: the dry doped material
• sample 1 of the present invention
• sample 2 wet doped material of the prior art
• sample 3 undoped NaAlH4
• Excellent agreement was found among samples which were prepared at different times.
• the data obtained for sample 2 was consistent with Bogdanovic's findings.
• the TPD measurements were made on samples of the three different materials.
• the plot of the hydrogen weight percentage desorbed as a function of temperature seen in Figure 1 is based on the integrated TPD data. While the catalytic effect of titanium is evident for both samples 1 and 2, of significant advantage the dehydrogenation temperature of sample 1 is seen to be about °30 C lower than that of sample 2.
• the inventors have found that the enhancement of the dehydrogenation kinetics of NaAlH 4 upon introduction of titanium to the material is highly sensitive to the doping method.
• the novel dry doping method of the present invention is much more effective for the generation of catalytically active titanium sites than the wet doping method previously reported. It is also significant that unlike the wet doped material, the kinetic enhancement of the dry doped material is undiminished over several dehydriding/ hydriding cycles. The results also indicate that the catalytic effect in the titanium doped material is due to that only a fraction amount of titanium is introduced into the host hydride.
• zirconium doped NaAlH 4 was prepared by homogenizing freshly recrystallized hydride with Zr(OPr) 4 under an atmosphere of argon. Hydrogen evolution from samples of the zirconium doped hydride was studied by thermal programmed deso ⁇ tion (TPD). Plots of the desorbed hydrogen weight percentage as a function of temperature are illustrated in Figure 4. The discontinuity in the deso ⁇ tion curves reflects the difference in activation energies of the dehydriding reactions as seen in equations 1 and 2.
• the rehydriding is also catalyzed by zirconium doping. As observed for titanium doped NaAlH 4 , recharging of the dehydrided materials can be achieved at 170°C and 150 atm of hydrogen pressure.
• An important aspect of a hydrogen storage material is its ability to perform after repeated dehydriding/rehydriding cycles.
• the TPD spectra of the zirconium containing materials showed excellent reproducibility.
• the temperature required for dehydriding is consistently 20 °C lower than for the first cycle. Similar behavior was observed in a parallel study of materials doped with 2 mol % titanium through homogenization method of the present invention.
• the temperature required for the dehydriding reactions is lowered by 20 °C after the preliminary dehydriding/rehydriding cycle.
• the onset of rapid dehydrogenation at 100° C in the titanium doped material is noteworthy as it suggests the application of these materials as hydrogen carriers for onboard fuel cells.
• the chain of advancement in the development of metal catalyzed NaAlH 4 is illustrated by comparison of the TPD spectra of the third dehydriding cycle of variety of doped materials.
• hydride which was doped with titanium through the method of Bogdanovic has a cyclable hydrogen capacity of 3.2 wt % .
• Titanium doping through the homogenization method of the present invention significantly enhances the kinetics of the first dehydriding reaction and improves the cyclable hydrogen capacity to 4.0 wt % .
• the zirconium doped material shows enhancement of the kinetics of the second dehydriding reaction and a further improved cyclable hydrogen capacity of 4.5 wt % .
• the kinetics of the first dehydriding reaction in the Zr doped material are inferior to those of the titanium doped material of the present invention.
• the inventors have found that the dehydriding kinetics of NaAlH 4 are significantly enhanced through zirconium doping. While zirconium is inferior to titanium as a catalyst for the dehydriding of NaAlH 4 to Na 3 AlH 6 and Al, it is a superior catalyst for the dehydriding of Na 3 AlH 6 to NaH and Al. The benefit of both catalytic effects can be realized in materials containing a combination of both titanium and zirconium catalysts. After the initial dehydriding/rehydriding cycle, NaAlH 4 which is doped with titanium and/or zirconium is stabilized with a greater than 4 wt % cyclable hydrogen. Finally, the occurrence of rapid dehydriding in the titanium containing materials at temperatures below 100 °C suggests their application as hydrogen carriers for onboard fuel cells.
• thermovolumetric analyzer (TV A), based on a modified Sievert's type apparatus, was used to characterize the gas-solid interaction between hydrogen and the sodium aluminum hydride systems.
• the TVA consisted of two high pressure stainless steel Parr reactors (Model 452HC-T316), one used to hold the sample and the other as a gas reservoir, between which very small precisely measured volumes of hydrogen may be transferred.
• the sample vessel contained an aluminum insert with two narrow cylindrical cavities.
• a K-type thermocouple was placed inside each of the cavities.
• One of the cavities contained the sample and the other was used as a temperature reference.
• the sample cavity was designed to insure intimate contact between the aluminum insert and the sample. This, together with the high thermal conductivity of the insert served to minimize temperature fluctuations within the sample resulting from the heat of reaction or rapid pressure change.
• the entire sample vessel could be heated and cooled using a PLD programmable controller unit that allows sample temperatures to be controlled and programmed to change between 196 and 673 °K.
• a PLD programmable controller unit that allows sample temperatures to be controlled and programmed to change between 196 and 673 °K.
• the entire sample vessel was placed inside a container surrounded by a mixture of dry ice and acetone.
• Hydrogen pressures inside the vessels were measured using high precision pressure transducers. Different size aluminum inserts were available to adjust the dead volume above the sample, allowing total pressure and pressure changes to be maintained within the range and precision of our instrumentation as sample size and hydrogen loading varied. The volumes of the sample vessel and gas reservoir and the gas flows between them were calibrated using hydrogen and argon.
• the gas system was constructed using high purity regulators, a VCR sealed manifold capable of operating under vacuum or at elevated pressure, diaphragm type shut- off valves, and micro valves to control gas flows between reactors.
• the gas lines and vessels were tested on regular basis for inboard or outboard gas leaks.
• System temperatures and pressures were recorded using a high data acquisition system together with a software developed for this task.
• the rates of hydrogen deso ⁇ tion for each of the three samples were measured using a thermal programmed deso ⁇ tion (TPD) technique.
• TPD thermal programmed deso ⁇ tion
• a sample of about 0.5 grams was weighted, and loaded into the high pressure reactor under argon atmosphere.
• the samples were then heated from room temperature to 280 °C at a rate of 2 °C per minute while maintaining low hydrogen over pressure in the sealed reactor.
• the rate of hydrogen deso ⁇ tion was measured as a function of temperature. On selected samples, the TPD measurements were repeated to insure the reproducibility of the samples and the measurements.
• NaAlH 4 and zirconium tetra-w-propoxide, Zr(OPr), (70 wt. % in propanol solution) were purchased from Aldrich Chemical Inc.
• NaAlH 4 was recrystallized from THF/pentane using standard Schlenk techniques with oxygen and water free solvents.
• Ti(OBu n ) 4 was used as purchased from Strem Chemical Inc.
• NaAlH 4 (0.54 g, 10 mmol) was combined with 94 ⁇ L of a 70 wt % solution of Zr(OPr) 4 in propanol.
• Homogenized samples were prepared by first manual mixing with a mortar and pestle for 5 minutes and then mechanical blending with a Wig-L-Bug electric grinder/mixer for 15 minutes. Titanium doped samples were similarly prepared using Ti(OBu n ) 4 (70 ⁇ L 0.20 mmol). Titanium/zirconium doped hydride was homogenized with 0.047 mL of a 70 wt % solution of Zr(OPr) 4 and Ti(OBu n ) 4 (35 ⁇ L, 0.10 mmol).
• TPD Thermal programmed desorption
• thermo volumetric analyzer based on a modified Sievert's type apparatus.
• the TVA system contained a high pressure reactor vessel with a PID programmable temperature controller unit. Hydrogen pressures inside the vessels were measured using high precision pressure transducers. Different size aluminum inserts were available to adjust the dead volume above the sample, allowing total pressures and pressure changes to be maintained within the range and precision of our instrumentation as sample size and hydrogen loading varied.
• the volumes of the sample vessel and gas reservoir and the gas flows between them were calibrated using hydrogen and argon.
• the gas system was constructed using high purity regulators, a VCR sealed manifold capable of operating under vacuum or at elevated pressure, diaphragm type shut-off valves, and micro- valves to control gas flows between reactors.
• the gas lines and vessels were tested on a regular basis for gas leaks. System temperatures and pressures were recorded using a high precision 16-bit National Instruments data acquisition system together with software developed for this task.
• the hydrogen desorption behavior of the samples was monitored as a function of temperature using a thermal programmed deso ⁇ tion (TPD) spectrum technique.
• Samples ( ⁇ 0.5 grams) were loaded into the high pressure reactor under argon atmosphere and heated from room temperature to 280 °C at a rate of 2°C per minute while maintaining low hydrogen ove ⁇ ressure in the sealed reactor. On selected samples, the TPD measurements were repeated to insure the reproducibility of the samples and the measurements.
• TPD thermal programmed deso ⁇ tion

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• 1999
  • 1999-07-14 KR KR1020017001604A patent/KR20010079623A/ko not_active Application Discontinuation
  • 1999-07-14 CN CN99810917A patent/CN1318033A/zh active Pending
  • 1999-07-14 CA CA002339656A patent/CA2339656A1/en not_active Abandoned
  • 1999-07-14 AU AU49972/99A patent/AU4997299A/en not_active Abandoned
  • 1999-07-14 JP JP2000563567A patent/JP2002522209A/ja active Pending
  • 1999-07-14 EP EP99934053A patent/EP1100745A1/en not_active Withdrawn
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