HYDROGEN STORAGE MATERIALS AND PROCESSES FOR PREPARING SAME

Abstract

The present invention relates to improved hydrogen storage materials and improved processes for their preparation. The hydrogen storage materials prepared by the processes described herein exhibit enhanced hydrogen storage capacity when used as hydrogen storage systems. The processes described herein may be undertaken on a commercial scale.

Claims

1.-166. (canceled)

167. A process for preparing a hydrogen storage material precursor comprising precipitating a manganese compound having one or more substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, or a combination thereof bound to the manganese via metal-carbon sigma bonds from (a) an inert solvent, (b) a solvent without a β-hydrogen, or a combination thereof, wherein (i) the substituted or unsubstituted alkyl or substituted or unsubstituted aryl groups in the manganese compound do not have a β-hydrogen, and (ii) the precipitate when hydrogenated results in a material in which the manganese has an oxidation state of from 0.2 to 1.5 and is capable of absorbing H.sub.2 via a Kubas interaction.

168. A process for preparing a hydrogen storage material comprising: (i) precipitating a manganese compound having one or more substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, or a combination thereof from (a) an inert solvent, (b) a solvent without a β-hydrogen, or a combination thereof, and (ii) hydrogenating the precipitate, wherein the manganese in the hydrogenated precipitate has an oxidation state of from 0.2 to 1.5 and the hydrogen storage material is capable of absorbing H.sub.2 via a Kubas interaction.

169. The process of claim 167, wherein the precipitation results in condensation of an initial manganese compound.

170. The process of claim 167, wherein the precipitate is prepared from a manganese compound that has two substituted or unsubstituted alkyl groups, and each substituted or unsubstituted alkyl group is linked to the manganese via a 2-electron 2-center single bond.

171. The process of claim 167, wherein the metal-carbon sigma bonds are not 3-center 2-electron bonds.

172. The process of claim 167, wherein the precipitate is prepared from a manganese compound that is (Me.sub.3Si—CH.sub.2).sub.2Mn.

173. The process of claim 167, wherein the solvent is an inert solvent (e.g., supercritical xenon, supercritical krypton, supercritical methane, supercritical CO.sub.2, or any combination thereof).

174. The process of claim 167, wherein the solvent is selected from supercritical xenon, supercritical krypton, supercritical methane, supercritical CO.sub.2, a tetralkylsilane (e.g., tetramethylsilane), adamantane, cubane, neopentane, xylene, trimethylbenzene (e.g., 1,3,5-trimethylbenzene), and any combination thereof.

175. The process of claim 167, wherein the solvent is 1,3,5-trimethylbenzene.

176. The process of claim 167, wherein the concentration of the manganese compound in the solvent is greater than about 3.1 g/100 mL.

177. The process of claim 167, wherein the precipitating step is performed in the absence of H.sub.2.

178. The process of claim 167, wherein the precipitating step involves thermal precipitation, photochemical precipitation, or a combination thereof.

179. The process of claim 167, wherein the precipitating step comprises heating the manganese compound and isolating the precipitate.

180. The process of claim 167, wherein the precipitate weighs greater than about 40% of the original weight of the manganese compound.

181. The process of claim 167, wherein the precipitate contains greater than about 40% by weight of residue other than manganese.

182. The process of claim 167, wherein the hydrogenated material is capable of absorbing H.sub.2 by Kubas interation and/or physisorption to a level of at least about 2 wt %, at least about 4 wt %, at least about 8 wt %, at least about 10 wt %, at least about 10.5 wt % or at least about 12 wt %.

183. The process of claim 167, wherein the hydrogenated material comprises MnH.sub.x, optionally further comprising residual hydrocarbon and/or solvent, where x is 0.2 to 1.5 and is capable of reversibly storing more than two H.sub.2 molecules per Mn.

184. The process of claim 167, wherein the manganese in the hydrogenated material comprises Mn(I) and Mn(II).

185. The process of claim 167, wherein the precipitate is formed by condensation of the manganese compound.

186. The process of claim 167, wherein the hydrogenated material is a bulk solid.

187. The process of claim 167, wherein the hydrogenated material is stable at room temperature.

188. The process of claim 167, wherein the hydrogenated material further comprises one or more additional metals.

189. The process of claim 188, wherein the one or more additional metals are selected from niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, iron, zirconium, zinc, gallium, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, and any combination thereof.

190. The process of claim 167, further comprising (i) subjecting the hydrogenated material to vacuuming, heating, or both, and optionally (ii) repeating one or more times (a) hydrogenation of the vacuumed and/or heated material and (b) subjecting the hydrogenated material to vacuuming, heating, or both.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0472] FIG. 1 depicts an embodiment of a storage system useful in the present invention.

[0473] FIG. 2 depicts an embodiment of the storage system attached to a hydrogen fuel cell.

[0474] FIG. 3 depicts an Infra Red spectrum of bis (trimethylsilylmethyl) manganese.

[0475] FIG. 4 depicts an Infra Red spectrum of a product of Example 1.

[0476] FIG. 5 depicts hydrogen adsorption/desorption measurements of the product of Example 1.

[0477] FIG. 6 depicts an Infra Red spectrum of a product of Example 2.

[0478] FIG. 7 depicts hydrogen adsorption/desorption measurements of the product of Example 2.

[0479] FIG. 8 depicts an Infra Red spectrum of a product of Example 3.

[0480] FIG. 9 depicts hydrogen adsorption/desorption measurements of the product of Example 3.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0481] Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0482] The term “comprising” is open ended and, in connection with a composition, refers to the elements recited. The term “comprising” as used in connection with the compositions described herein can alternatively cover compositions “consisting essentially of” or “consisting of” the recited components.

[0483] The term “coordinate” as used here is not limited to a specific type of interaction between a metal center and hydrogen. For example, in one embodiment, the interaction between a metal center and hydrogen is a Kubas interaction.

[0484] The term “Kubas interaction” refers to hydrogen bound in a non-dissociative manner as a dihydrogen molecule to a transition metal center. In a Kubas interaction, free d-electrons of a metal centre interact with hydrogen. Specifically, where the metal centre has a low coordination number, the dihydrogen shares both of its σ-bonding electrons with the metal centre, and the metal centre back donates electrons by overlap of its π symmetry d-orbital with the empty antibonding σ* empty orbital of the dihydrogen. This results in a lengthening of the H—H bond (without rupture) and a shift to a lower wavenumber for the H—H resonance (see, e.g. J. Am. Chem. Soc., 119, 9179-9190, 1997).

[0485] Without wishing to be bound by theory, the inventor theorizes that one or more (such as 2 or more, such as 3, 4 or 5) H.sub.2 molecules interact with the metal centers by Kubas interactions to form metal hydrides of the formula MH.sub.x (optionally further comprising residual hydrocarbon and/or solvent) in which x can be approximately an even number, e.g., about 4, about 6, about 8, about 10 or about 12. However, bimolecular and/or free radical processes may also occur leading to metal hydrides of the formula MH.sub.x in which x can approximately an odd number, e.g., about 3, about 5, about 7, about 9, about 11 or about 13. Additionally, mixed metal hydrides, in which variable x is a non integer may also be formed by continuous (not stepwise) adsorption.

[0486] The term “substantially free” as used herein means containing less than about 2 wt %, such as less than about 1 wt %, less than about 0.5 wt %, less than about 0.1 wt %, less than about 0.05 wt %, less than about 0.01 wt %, less than about 0.005 wt % or less than about 0.001 wt % of a specified element or compound.

[0487] In one embodiment, the term “residue” refers to any carbon containing group that may be present in a precipitate or hydrogenated precipitate described herein. For example, the residue may be a solvent used in the formation of the precipitate or hydrogenated precipitate that has not been fully removed during the synthesis process. Another example of a residue may be a ligand (e.g., trimethylsilylmethyl, mesityl, benzyl or neopentyl) that is not fully removed from the metal center during formation of the precipitate or hydrogenated precipitate. The residue may also be a compound (e.g., a protic compound, such as methanol) that is added to the hydrogenated precipitate in order to increase microporosity of the hydrogenated precipitate structure (e.g., by forming bridging methoxide ligands within the structure), thereby facilitating H.sub.2 moving in and out of the hydrogenated precipitate. The term “residue” may also refer to residual metal halide, such as MgCl.sub.2, ZnCl.sub.2, LiCl, LiI, etc.

[0488] As used herein, in one embodiment the term “thermodynamically neutral” refers to the net enthalpy changes associated with either the process of hydrogen adsorption and/or the process of hydrogen desprotion when averaged over the whole metal hydride sample. For example, the net enthalpy changes associated with either the process of hydrogen adsorption and/or the process of hydrogen desprotion, when averaged over the bulk sample, are close to 0 kJ mol.sup.−1 H.sub.2. Typically, hydrogen adsorption on a microscopic basis exhibits a range of enthalpies between about −5 and −70 kJ mol.sup.−1 H.sub.2. Without wishing being bound to theory, the inventor theorizes that the energy required by external pressure to open up binding sites in the metal hydride is approximately equal and opposite to the exothermic M-H bond forming process, resulting in effective enthalpy buffering and thermodynamic neutrality. Also without being bound to theory, the inventor theorizes that the energy required to open up the hydrogen binding sites in the metal hydrides described herein is provided by the gradually increasing external pressure of the hydrogen, which is roughly equal and opposite in value to the energy involved in hydrogen binding to the metal enters resulting in thermodynamic neutrality, and can be rationalised by the energy required to twist the amorphous structure into a conformation favourable for hydrogen binding. See, e.g., Skipper et al., J. Phys. Chem. C, 116, 19134, 2012.

[0489] As used herein, the term “alkyl” refers to a straight or branched chain saturated hydrocarbon moiety. In one embodiment, the alkyl group is a straight chain saturated hydrocarbon. Unless otherwise specified, the “alkyl” or “alkylene” group contains from 1 to 24 carbon atoms. Representative saturated straight chain alkyl groups include, e.g., methyl, ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl. Representative saturated branched alkyl groups include, e.g., isopropyl, sec-butyl, isobutyl, tert-butyl, neopentyl, and isopentyl. In a preferred embodiment, an “alkyl” group does not contain a β hydrogen substituent.

[0490] As used herein, the term “substituted alkyl” refers to an alkyl group as defined above substituted by, for example, one or more heteroatoms, such as, Si, Se, O, N and S.

[0491] As used herein, the term “aryl” refers to an aromatic hydrocarbon (mono- or multi-cyclic) having from 6 to 24 carbon atoms (e.g., phenyl, naphthyl), bound to the metal center via a metal-carbon bond.

[0492] As used herein, the term “substituted aryl” refers to an aryl group as defined above substituted by, for example, one or more alkyl groups (e.g., methyl), and/or one or more heteroatoms, such as, Si, Se, P, O, N and S.

[0493] As used herein, the terms “hydrogenated precipitate” and “metal hydride” may be used interchangeably. The “hydrogenated precipitate” and “metal hydride” are capable of absorbing H.sub.2 via a Kubas interaction.

[0494] As used herein, the term π-acidic ligand refers to a ligand that donates electron density into a metal d-orbital from a 2-symmetry bonding orbital between the atoms. PP-acidic ligands are ligands that have a relatively low-lying LUMO that has the appropriate symmetry to interact with a d-orbtal (dxy, dxz, dzy) on the transition metal centre and the resultant molecular orbital formed will have pi-symmetry. Suitable non-limiting examples of π-acidic ligands that may be used herein include, but are not limited to, CO, N.sub.2, CN, O.sub.2, NO.sup.−, CO.sub.2, olefins, carbenes, isocyanides, isothiocyanates, and any combination thereof. In one embodiment, the π-acidic ligand is CO.

[0495] As used herein, the terms “precipitate” and “hydrogen storage material precursor” may be used interchangeably. The “precipitate” or “hydrogen storage material precursor” is hydrogenated to provide the “hydrogenated precipitate” or “metal hydride.”

[0496] In one embodiment, the term “inert solvent” refers to a solvent that does not undergo C—H activation with the transition metal (e.g., M.sup.1) center. The term “inert solvent” may also refer to a solvent that does not otherwise complex with the transition metal (e.g., M.sup.1, such as manganese) center.

Hydrogenated Precipitates

[0497] In one embodiment, any of the hydrogenated precipitates described herein has a BET surface area of less than about 5 m.sup.2/g, such as less than about 4 m.sup.2/g, such as less than about 3 m.sup.2/g, less than about 2 m.sup.2/g, less than about 1.5 m.sup.2/g or less than about 1.0 m.sup.2/g, such as about 0.6 m.sup.2/g.

[0498] In another embodiment, any of the hydrogenated precipitates described herein has a BET surface area of about 2 m.sup.2/g or greater, such as about 5 m.sup.2/g or greater, about 7.5 m.sup.2/g or greater, about 10 m.sup.2/g or greater, about 25 m.sup.2/g or greater, about 50 m.sup.2/g or greater, about 75 m.sup.2/g or greater, about 100 m.sup.2/g or greater, about 150 m.sup.2/g or greater, about 200 m.sup.2/g or greater, about 250 m.sup.2/g or greater, about 275 m.sup.2/g or greater, about 300 m.sup.2/g or greater, about 350 m.sup.2/g or greater, about 400 m.sup.2/g or greater, about 450 m.sup.2/g or greater or about 500 m.sup.2/g or greater. For example, the metal hydride has a BET surface area of about 377 m.sup.2/g or 391 m.sup.2/g. In another embodiment, any of the hydrogenated precipitates described herein has a BET surface area of up to about 2000 m.sup.2/g, such as 1000-2000 m.sup.2/g or 1500-200 m.sup.2/g.

[0499] In other embodiments, the BET surface area is from about 2 m.sup.2/g to about 1000 m.sup.2/g, such as from about 10 m.sup.2/g to about 750 m.sup.2/g, from about 50 m.sup.2/g to about 500 m.sup.2/g, from about 100 m.sup.2/g to about 500 m.sup.2/g, from about 250 m.sup.2/g to about 500 m.sup.2/g, from about 300 m.sup.2/g to about 500 m.sup.2/g. In one embodiment, the BET surface area is from about 300 m.sup.2/g to about 400 m.sup.2/g.

[0500] In one embodiment, the hydrogenated precipitates described herein are in the form of a gel. In one embodiment, the hydrogenated precipitates described herein are in the form of a solid (e.g., a powder). In one embodiment, any of the hydrogenated precipitates described herein is a bulk solid, for example, a stable bulk solid at room temperature. In one embodiment, the hydrogenated precipitates described herein are polymeric (e.g., polymeric in the bulk phase). In one embodiment, the hydrogenated precipitates described herein are in the form of a pellet.

[0501] In one embodiment, any of the hydrogenated precipitates described have a pore diameter of about 2 nm.

[0502] In one embodiment, any of the hydrogenated precipitates described herein have a porosity of between about 5 and about 80%, such as between about 5 and about 70%, between about 5 and about 60%, between about 5 and about 50%, between about 5 and about 40%, between about 5 and about 30% or between about 5 and about 20%.

[0503] In further embodiments, any of the hydrogenated precipitates described herein exhibit a gravimetric hydrogen absorption at least about 2%, at least about 3%, at least about 4%, at least about 5%, at least about 6%, at least about 7%, at least about 8%, at least about 9%, at least about 10%, at least about 11%, at least about 12%, at least about 13% or at least about 14%, e.g., in an amount up to about 14%, such as from about 2.0% to about 14.0%, from about 8.0% to about 12.0%, or about 3.5%, about 7.0%, about 10.5%, about 14%) based upon 100% total weight of the metal hydride without molecular hydrogen stored in it.

[0504] In another embodiment, any of the hydrogenated precipitates described herein are free or substantially free of metal ions (other than titanium, vanadium, chromium, iron, cobalt, nickel and/or copper). In another embodiment, any of the hydrogenated precipitates described herein are free or substantially free of organic residue (e.g., organic ligands or solvents used during the synthesis of the hydrogenated precipitate). In another embodiment, any of the hydrogenated precipitates described herein are free or substantially free of metal ions (other than titanium, vanadium, chromium, iron, cobalt, nickel and/or copper) and free or substantially free of organic residue (e.g., organic ligands or solvents used during the synthesis of the hydrogenated precipitates).

[0505] In another embodiment, any of the metal hydrides described herein may contain a transition metal in more than one oxidation state (e.g., M(I)/M(II), M(0)/M(I)/M(II)) wherein M is a metal as described herein.

[0506] The hydrogenated precipitates described herein preferably have sufficient microporosity (which may or may not be visible by nitrogen adsorption) to permit H.sub.2 to move in and out of the metal hydride framework to the active binding sites. In one embodiment, the hydrogenated precipitate has sufficient microporosity to permit: (i) H.sub.2 to diffuse in and out of the material and the active binding sites of the metal hydride; (ii) the metal to coordinate with H.sub.2 via, for example, a Kubas interaction; and (iii) absorption of H.sub.2 in an amount of about 2.0% to about 14.0% (based upon 100% total weight of the metal hydride without hydrogen stored in it). The hydrogenated precipitates may be incorporated into a hydrogen storage system as described herein.

[0507] In yet another embodiment, any of the hydrogenated precipitates described herein is crystalline. In one embodiment, and without being bound by theory, the H.sub.2 may move through the structure via a shuttle mechanism whereby it binds to the metal on one side and desorbs on the other to penetrate further into the structure, or moves through lammellai between crystalline planes.

[0508] In one embodiment, the hydrogenated precipitates described herein are amorphous or substantially amorphous (e.g., with little (e.g., nanoscopic order) or no long range order in the position of the atoms in the hydride structure). In one embodiment, the hydrogenated precipitates described herein contain less than about 20% crystallinity, such as less than about 10%, less than about 5%, less than about 2.5%, less than about 1%, less than about 0.5% or or less than about 0.1% crystallinity, as measured, for example, by X-ray diffraction using a Cu Kα radiation (40 kV, 40 mA) source. Hydrogenated precipitates having closed packed structures are desirable due to their higher volumetric densities, so long as they permit diffusion of H.sub.2 to the metal binding sites within them. Where the closed packed structure of a hydrogenated precipitate does not permit diffusion of H.sub.2 to the metal binding sites, the hydrogenated precipitate preferably does not have a closed packed structure.

[0509] In one embodiment, the hydrogenated precipitates described herein are greater than 80% amorphous, such as greater than about 85%, greater than about 90%, greater than about 95%, greater than about 99% or greater than about 99.5% amorphous, as measured, for example, by X-ray diffraction using a Cu Kα radiation (40 kV, 40 mA) source.

[0510] In another embodiment, any of the hydrogenated precipitates described herein may contain a minor amount (e.g., up to 0.5 moles total) of an impurity selected from phosphines (e.g., trimethylphosphine), ethers, water, alcohols, amines, olefins, sulfides, nitrides, and combinations thereof. The phosphine (e.g., trimethylphosphine), ether, water, alcohol, amine, olefin (e.g., 1-hexene) sulfide or nitride residues may remain from their use in the synthesis of the metal hydride or may be formed as byproducts during the synthesis. In one embodiment, any of the hydrogenated precipitates of the present invention may contain less than about 10.0 wt %, less than about 9.0 wt %, less than about 9.0 wt %, less than about 7.5 wt %, less than about 5.0 wt %, less than about 4.0 wt %, less than about 3.0 wt %, less than about 2.0 wt %, less than about 1.0 wt %, less than about 0.75 wt %, less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.25 wt %, less than about 0.2 wt %, less than about 0.1 wt %, less than about 0.05 wt %, less than about 0.01 wt %, less than about 0.005 wt % or less than about 0.001 wt % of a phosphine (e.g., trimethylphosphine), ethers (e.g., Et.sub.2O, THF, dioxane), water, alcohol, amine, olefin (e.g., 1-hexene), sulfide or nitride residue, or a combination thereof. In a preferred embodiment, the hydrogenated precipitate is free or substantially free of a phosphine (e.g., trimethylphosphine), ethers, water, alcohol, amine, olefin, sulfide or nitride residue, or a combination thereof. In addition, in embodiments where impurities are found, hydrogenated precipitates may also contain minor amounts (e.g., up to 0.5 moles total) of metal hydroxides (M-OH) and metal ethers (M-O-M) from the hydrolysis of metal alkyl species with residual water contained within the reaction mixture.

[0511] In certain embodiments, any of the hydrogenated precipitates contain less than about 10.0 wt % of lithium or magnesium, or a combination thereof. These lithium and magnesium residues may remain from their use in the synthesis of the hydrogenated precipitates. For example, any of the hydrogenated precipitates may contain less than about 9.0 wt %, less than about 8.0 wt %, less than about 7.5 wt %, less than about 5.0 wt %, less than about 4.0 wt %, less than about 3.0 wt %, less than about 2.0 wt %, less than about 1.0 wt %, less than about 0.75 wt %, less than about 0.5 wt %, less than about 0.25 wt %, less than about 0.1 wt % or less than about 0.05 wt %, less than about 0.01 wt %, less than about 0.005 wt %, or less than about 0.001 wt % of lithium or magnesium or a combination thereof. In another embodiment, any of the hydrogenated precipitates contain less than about 0.5 wt % of lithium or magnesium, or a combination thereof. For example, any of the hydrogenated precipitates may contain less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.25 wt %, less than about 0.2 wt %, less than about 0.1 wt %, less than about 0.05 wt %, less than about 0.01 wt %, less than about 0.005 wt % or less than about 0.001 wt % of lithium or magnesium or a combination thereof. In a preferred embodiment, the hydrogenated precipitate is free or substantially free of lithium or magnesium, or a combination thereof.

[0512] The hydrogenated precipitates of the present invention may contain halogen. For instance, the hydrogenated precipitates may contain less than about 20.0 wt % of a halogen, such as less than about 10.0 wt % of a halogen (such as Br.sup.−, Cl.sup.−, or I.sup.−). These halogen residues may remain from their use in the synthesis of the hydrogenated precipitate (for instance, from the use of a Grignard reagent). For example, any of the hydrogenated precipitates may contain less than about 9.0 wt %, less than about 8.0 wt %, less than about 7.5 wt %, less than about 5.0 wt %, less than about 4.0 wt %, less than about 3.0 wt %, less than about 2.0 wt %, less than about 1.0 wt %, less than about 0.75 wt %, less than about 0.5 wt %, less than about 0.25 wt %, less than about 0.1 wt % less than about 0.05 wt %, less than about 0.01 wt %, less than about 0.005 wt %, or less than about 0.001 wt % of halogen. In a preferred embodiment, the hydrogenated precipitate is free or substantially free of halogen.

[0513] In other embodiments, any of the hydrogen storage materials (metal hydrides, hydrogenated precipitates) described herein further comprise up to about 5% by weight of bound π-acid ligand (e.g., CO, N.sub.2, CN, O.sub.2, NO.sup.−, CO.sub.2, olefins, carbenes, isocyanides, isothiocyanates, or any combination thereof), such as about 0.1% to about 5% by weight, about 0.1% to about 4% by weight, about 0.1% to about 3% by weight, about 0.1% to about 2% by weight, about 0.1% to about 1% by weight, about 0.1% to about 0.9% by weight, about 0.1% to about 0.8% by weight, about 0.1% to about 0.7% by weight, about 0.1% to about 0.6% by weight, about 0.1% to about 0.5% by weight, about 0.1% to about 0.4% by weight, about 0.1% to about 0.3% by weight, or about 0.1% to about 0.2% by weight bound CO. Without wishing to be bound by theory, the present inventor theorizes that the presence of the π-acid ligand (such as, e.g., CO) may stabilize the structure of the hydrogen storage material (metal hydride, hydrogenated precipitate) due to the propensity of CO to form bridges between metal centres. For example, in one embodiment, the π-acid ligand (such as, e.g., CO) is terminally bound to the metal center (M). In another embodiment, the π-acid ligand (such as, e.g., CO) bridges between two metal (M) centers in a ketonic fashion (e.g., (M-(CO)-M). In another embodiment, the π-acid ligand (such as, e.g., CO) bridges two metal (M) centers in a multidentate fashion (e.g., M-C—O-M). In another embodiment, the π-acid ligand (such as, e.g., CO) bridges three metal (M) centers. The bound π-acid ligand (such as CO) may add structural stability through cycling and also mechanical stability to the microporous structure to vibrations, because of strong M/π-acid ligand bridging interactions.

[0514] In one embodiment, any of the hydrogen storage materials described herein (such as metal hydrides and hydrogenated precipitates) contain a π-acid ligand added in an amount ranging from about 0.1 to about 5 mol %, such as about 1 to about 5 mol %, about 1 to about 4 mol %, about 1 to about 3 mol %, or about 1 to about 2 mol %, relative to the metal (M) center, such as Mn.

[0515] In one embodiment, any of the hydrogen storage materials described herein (such as metal hydrides and hydrogenated precipitates) contain a π-acid ligand present. In one embodiment, any of the hydrogen storage materials (metal hydrides, hydrogenated precipitates) described herein contain a π-acid ligand present as a residue of one or more of the reactants.

Hydrogen Storage

[0516] In another embodiment, the present invention relates to a method of storing hydrogen comprising providing a hydrogenated precipitate according to any of the embodiments described herein (e.g., a hydrogenated precipitate prepared according to any of the processes described herein), adding hydrogen to the hydrogenated precipitate, and allowing the hydrogen to coordinate to the hydrogenated precipitate. The storing of hydrogen may be carried out in a storage system.

[0517] One embodiment of a storage system suitable for hydrogen storage is a pressure vessel. For example, the pressure vessel may hold the metal hydride of the present invention at a temperature of up to 200° C., e.g., from about −100 to about 150° C., from about −50 to about 0° C., from about −25 to about 0° C., from about 0 to about 150° C., from about 0 to about 50° C., from about 10 to about 30° C. or from about 20 to about 25° C. In one embodiment, the storage system is substantially free of oxygen.

[0518] Hydrogen may be added to the storage system (e.g., a pressure vessel) and stored using the hydrogenated precipitates of the present invention. In one embodiment, no heating is required when adding hydrogen to the pressure vessel for storage.

[0519] The amount of hydrogen that can be stored by the hydrogenated precipitates of the present invention is proportional to the pressure in the storage system. For example, at higher pressures, more hydrogen can be stored by the metal hydrides of the present invention. The pressure in the storage system may be increased by adding hydrogen to the storage system. Without wishing to be bound by any particular theory, the inventor theorizes that as the pressure is increased, the number of Kubas interactions per metal centre may increase. As noted above, however, this process will appear continuous in the bulk state, resulting in the formation of a bulk material containing hydrogenated precipitates having a mixture of coordinated hydrogen molecules, and, therefore, an overall non-integer stoichiometry of manganese to hydrogen. Furthermore it may be possible (e.g., via a free radical and/or bimolecular process) to form molecular species of the formula MH.sub.3, MH.sub.5, MH.sub.7, MH.sub.9 and MH, etc.

[0520] In further embodiments, any of the hydrogenated precipitates described herein optionally contain one or more additional metals (e.g., a metal other than titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper). For example, the hydrogenated precipitate may contain one or more additional metals selected from sodium, potassium, aluminum, beryllium, boron, calcium, lithium, magnesium and combinations thereof. In an alternate embodiment, the hydrogenated precipitate may contain one or more additional metals (e.g., a metal other than titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper) wherein the one or more additional metals is a period 4, 5, 6, 7, 8, 9, 10, 11 and/or 12 transition metal, or a lanthanide, that forms a hydride upon treatment with hydrogen. For example, the hydrogenated precipitate may contain one or more additional metals selected from zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, and combinations thereof. In one embodiment, any of the hydrogenated precipitates described herein may optionally contain one or more additional period 4, period 5 or period 6 transition metals. In another embodiment, the hydrogenated precipitates may contain one or more additional metals selected from iron, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, and combinations thereof. The one or more additional metals may be present in an amount of about 50 wt. % or less, about 40 wt. % or less, about 30 wt. % or less, about 25 wt. % or less, about 20 wt % or less, about 10 wt % or less, about 5 wt % or less, about 1 wt % or less, about 0.75 wt % or less, about 0.5 wt % or less, about 0.25 wt % or less, about 0.1 wt % or less, about 0.05 wt % or less or about 0.01 wt % or less. In one embodiment, the hydrogenated precipitates described herein contain no additional metal (e.g., no metal other than manganese).

[0521] The hydrogen pressure in the system may be increased using a compressor, such as a gas compressor, which pumps hydrogen into the system. Preferably, the hydrogen pressure in the system is increased to about 30 atm or more. For example, the hydrogen pressure in the system may be increased to from about 30 atm to about 500 atm, from about 50 atm to about 200 atm, or from about 75 atm to about 100 atm.

[0522] The system preferably has a temperature of (or operates at) up to 200° C., such as about −200° C. to 150° C. (e.g., about −100° C. to 150° C.), about −200° C. to 100° C., about 0° C. to 50° C., about 10° C. to 30° C., or about 20° C. to 25° C. In one embodiment, the system has a temperature (or operates at) about 25° C. to about 50° C. The system is preferably free of oxygen to prevent the oxidation of metal in the system. In one embodiment, the method of storing and releasing hydrogen in a system of the present invention may be carried out without adding heat to and/or cooling the system. In another embodiment, the method of storing and releasing hydrogen in a system of the present invention may be carried out by adding heat to and/or cooling the system.

[0523] In a further embodiment, the hydrogen is released from the storage system. For example, this may be accomplished by reducing the pressure of hydrogen in the system. In one embodiment, no heating is required in order to release the hydrogen from the metal hydride. For example, a valve in the storage system may be opened to allow hydrogen gas to escape from the system, thus decreasing the pressure in the storage system. In one embodiment, about 100% of the stored hydrogen is released. In additional embodiments, greater than about 50%, greater than about 55%, greater than about 60%, greater than about 70%, greater than about 75%, greater than about 80%, greater than about 90%, greater than about 95%, greater than about 97.5%, greater than about 99% or greater than about 99.5% of the hydrogen is released. The step of releasing the hydrogen pressure in the system may be carried out by allowing hydrogen gas to escape from the system, thus decreasing the hydrogen pressure. For instance, the step of releasing the hydrogen pressure may decrease the hydrogen pressure in the system to 100 atm or less (such as to 50 atm or less, 30 atm or less, or 20 atm or less). In another embodiment, the hydrogen is released from the storage system by increasing the temperature of the system.

[0524] Hydrogen may be added or released from the system at any point throughout the entire pressure gradient of the system without any adverse effects to the storage capacity of the system. In certain embodiments, hydrogen may be added or released from the system any number of times without any adverse effect to the storage capacity of the system. For example, the system can be filled with hydrogen and emptied of hydrogen at least 100, such as at least 200, at least 500, at least 1000 or at least 1500 times without a significant decrease in the storage capacity of the system.

[0525] In one embodiment, the storage system (e.g. pressure vessel) is a fuel tank in a vehicle, such as a truck or automobile.

[0526] FIG. 1 depicts an embodiment of a storage system useful in the present invention. FIG. 2 depicts an embodiment of the storage system attached to a hydrogen fuel cell. The system 10 comprises a tank body 12 which is made of a material that is impermeable to hydrogen gas, thus preventing undesired leaking of the hydrogen gas out of the tank body 12. For example, the tank body 12 is made of metal, such as, e.g., steel or aluminum. Alternatively, the tank body 12 is made of a composite material, such as a composite of fibreglass and aramid. In another embodiment, the tank body 12 is made of a carbon fibre with a liner. The liner may be a polymer liner, such as a thermoplastic liner or a metal liner, such as a steel liner or an aluminum liner. In one embodiment the tank is an aluminum medical oxygen tank (e.g., an M-150 Al tank. See, e.g., http://nashvilleemsshop.com/Oxygen-Cylinder-M150_p_787.html).

[0527] The hydrogenated precipitate 14 is present inside the tank body 12. In FIG. 1, the hydrogenated precipitates 14 is in a gel form. The hydrogenated precipitates 14 may partially fill or totally fill the tank body 12. In certain embodiments, the hydrogenated precipitates may be present as a coating on a support or in pellet form, depending upon the requirements for pressure drops in the tank body. In additional embodiments, the hydrogenated precipitates may be present in admixture with other compounds (such as a binder) which enhance the structural integrity and other properties of the coating or the pellet.

[0528] A first passage 16 leads to a first opening 18 in the wall of the tank body 12. A first valve 20 controls the flow of hydrogen gas through the first opening 18.

[0529] A second passage 22 extends from a second opening 24 in the wall of the tank body 12. A second valve 26 controls the flow of hydrogen gas through the second opening 24.

[0530] The first valve 20 and the second valve 26 can be any type of valve that controls the flow of hydrogen gas through the first opening 18 and the second opening 24, respectively. For example, the first valve 20 and the second valve 26 can be ball valves or gate valves.

[0531] In one embodiment, hydrogen is added to the system 10 as follows. A gas compressor 32 pumps hydrogen gas into the first passage 16. The first valve 20 is opened to allow the hydrogen gas to flow through the first opening 18 and into the tank body 12.

[0532] A passage tube 28 is in gaseous communication with the first opening 18 and extends into the interior of the tank body 12. The passage tube 28 facilitates the distribution of the hydrogen gas to the hydrogenated precipitate 14. In one embodiment, the passage tube 28 is made of a material that is permeable to the hydrogen gas. This allows the hydrogen gas to pass through the wall of the passage tube 28 and into contact with the hydrogenated precipitate 14. The passage tube is also preferably made of a material that is impermeable to the metal hydride 14, thus preventing the hydrogenated precipitate 14 from entering into the interior of the passage tube 28. The passage tube 28 preferably opens into the interior of the tank body 12. The opening of the passage tube 28 is preferably covered with a filter 30 which prevents the hydrogenated precipitate 14 from entering into the interior of the passage tube 28.

[0533] When the compressor 32 pumps hydrogen gas into the tank body 12, there is an increase of the hydrogen pressure inside the tank body 12. When the hydrogen pressure inside the tank body is increased, the hydrogenated precipitate 14 is able to coordinate with a greater amount of hydrogen. Preferably, the increase in pressure causes an increase in the number of Kubas interactions per metal centre in the metal hydride 14. After the desired amount of hydrogen has been added to the system, the valve 20 is closed.

[0534] When desired, hydrogen may be released from the system 10 as follows. The second valve 26 is opened, which allows hydrogen gas to flow out of the tank body 12 through the second opening 24. When hydrogen gas flows out of the tank body through the second opening 24, there is a decrease in pressure inside the tank body 12. When the pressure is decreased inside the tank body 12, the hydrogenated precipitate 14 releases hydrogen. For example, the decrease in pressure may cause a decrease in the number of Kubas interactions per metal centre of the hydrogenated precipitate 14.

[0535] Hydrogen that is released by the hydrogenated precipitate 14 can flow out of the tank body 12 through the second opening 24. As shown in FIG. 2, the hydrogen can flow through the second passage 22 to a fuel cell 36. The fuel cell 36 preferably uses hydrogen as a fuel and oxygen as an oxidant to produce electricity. Typically, a filter is present at the second opening 24 in order to prevent loss of particulates downstream.

[0536] In an alternative embodiment, the storage system of the present invention comprises a storage tank with a single opening. In this embodiment, hydrogen flows both into and out of the storage tank through the single opening. A valve is used to control the flow of hydrogen through the opening. Since the enthalpies of H.sub.2 binding are moderate to thermodynamically neutral and binding may be controlled by pressure, the tank may not need an exotic heat management system for most applications, unlike many prior hydrogen storage systems.

[0537] In one embodiment, the system is portable. As such, the system can be transported to a filling station to be filled with hydrogen. After being filled with hydrogen, the system can then be transported to a site where the hydrogen energy is to be used. Applications for this system include, but are not limited to, vehicles, airplanes, homes, buildings, and barbeques.

EXAMPLES

[0538] The present invention will now be further described by way of the following non-limiting examples. In applying the disclosure of these examples, it should be kept clearly in mind that the examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention in any way as many variations and equivalents that are encompassed by the present invention will become apparent to those skilled in the art upon reading the present disclosure.

Example 1

[0539] 2.0 g of analytically pure bis (trimethylsilylmethyl) manganese (7.03 mmol) (see FIG. 3) was placed in a pressure vessel under an atmosphere of argon (Ar) with 100 mL of dry deoxygenated tetramethylsilane and charged with 2.0 mL of CO (0.09 mmol) by syringe. The sealed mixture was heated with stirring to 110° C. for 48 hours and subsequently the solvent was removed in vacuo (10.sup.−3 torr). The vessel was then charged with 10% H.sub.2 in Kr to 80 bar and then heated to 80° C. for 4 hours followed by 5 minutes vacuum (10.sup.−3 torr) at 80° C. After cooling to room temperature, the pressure was released and the dark grey material collected. Yield=0.936 g. The Infra Red spectrum (FIG. 4) shows intense C—H stretches from 2800-3000 cm.sup.−1 and two bridging CO stretches at 1730 cm.sup.−1 1640 cm.sup.−1. Hydrogen adsorption/desorption measurements (FIG. 5; bottom trace (red)=adsorption, top trace (blue)=desorption) showed 2.5 wt % excess adsorption at 80 bar and 298 K.

Example 2

[0540] 2.0 g of analytically pure bis (trimethylsilylmethyl) manganese (7.03 mmol) (see FIG. 3) was placed in a Schlenk tube with 0.040 g of Mn.sub.2(CO).sub.10 (10 μmol) and 50 mL of dry deoxygenated 1,3,5 mesitylene was then added under an atmosphere of Ar. The mixture was heated with stirring to 130° C. for 24 hours and the solvent then boiled off in vacuo. The resulting solid was then placed in a Setaram hydrogen storage PCT vessel and subject to 4 hours H.sub.2 (80 bar, 80° C.) followed by 5 minutes vacuum (10.sup.−3 torr) at 80° C. Yield=0.823 g. The Infra Red spectrum (FIG. 6) shows C—H stretches from 2800-3000 cm.sup.−1 and one bridging CO stretch at 1640 cm.sup.−1. Hydrogen adsorption measurements (FIG. 7) of an 80 mg sample show 2.6 wt % excess adsorption at 105 bar and 298 K (bottom trace), which was adjusted to 4.4 wt % adsorption (top trace) after taking into account weight loss from 80 mg to 51 mg during measurement.

Example 3

[0541] 2.0 g of analytically pure bis (trimethylsilylmethyl) manganese (7.03 mmol) (see FIG. 3) was placed in a pressure vessel under an atmosphere of Ar and charged with 2.0 mL of CO (0.09 mmol). The vessel was then pressurized with methane to 80 bar and heated to 110° C. for 48 hours. The pressure was then released and the vessel was then charged with 10% H.sub.2 in CH.sub.4 to 80 bar and then heated to 80° C. for 4 hours followed by 5 minutes vacuum (10.sup.−3 torr) at 80° C. This was repeated a total of 5 times. The black solid (0.480 g) was collected. The Infra Red spectrum (FIG. 8) shows C—H stretches from 2800-3000 cm.sup.−1 and one bridging CO stretch at 1646 cm.sup.−1. Hydrogen adsorption/desorption measurements (FIG. 9, bottom trace (red)=adsorption, top trace (blue)=desorption) shows 8.4 wt % excess adsorption at 85 bar and 298 K. This result remained unchanged after heating 4 hours at 180° C. under vacuum (10.sup.−3 torr), or 4 hours in a Schlenk tube immersed at room temperature in an ultrasonic bath.

Example 4

[0542] 50 g (162 mmol) of MnI.sub.2 (see Chem. Rev., 109, 1435, 2009) in 1000 mL of diethyl ether is treated with 21.4 g (162 mmol) of dilithio 1,3,5 mesitylene (prepared according to the method of Meyer, Tetrahedron, 32, 51-56, 1976) under argon in 250 mL diethyl ether by drop-wise addition at −78° C. The solution is allowed to warm to room temperature and stirred overnight. The solvent is then removed in vacuo and the solid extracted into toluene and filtered to remove LiI. The toluene is then removed in vacuo to afford the polymeric mesityl Mn species, which is characterized by Infra-Red spectroscopy and elemental analysis. The product is then hydrogenated in the solid state or in a supercritical solvent (e.g., supercritical Xe, supercritical Kr, supercritical methane, supercritical CO.sub.2, or any combination thereof) to afford the hydrogen storage material.

[0543] The polymeric mesityl Mn species may also be prepared by heating bis(trimethylsilylmethyl)manganese in 1,3,5-mesitylene. CH-activation of the benzylic positions with elimination of tetramethylsilane leads to metathesis of the alkyl groups by Le Chatellier's Principle, as evidenced by the presence of C—C aromatic stretches in the Infra Red spectrum of the resulting product.

Example 5

[0544] 50 g of bis(trimethylsilylmethyl) manganese is placed in a high-pressure reactor equipped with a stirrer. The reaction vessel is then pressurized to 50 bar with high purity Xe (N5.0=99.999%) and heated to 100° C. The vessel is then further pressurized to 100 bar and the supercritical solution stirred for 24 hours. Cooling the vessel and depressurization affords a dark grey solid, which shows substantial hydrocarbon remaining by Infra Red spectroscopy. The product is then hydrogenated in the solid state or in a supercritical solvent (e.g., supercritical Xe, supercritical Kr, supercritical methane, supercritical CO.sub.2, or any combination thereof) to afford the hydrogen storage material.

[0545] Optionally, the process described above is performed in one step using a supercritical Xe/H.sub.2 or supercritical Kr/H.sub.2 mixture. The sequence of steps, reaction temperatures, relative proportions of gas mixtures and pressures are adjusted to tune the final density, porosity, hydrogen storage properties, and bulk form (e.g., powder, foam, puck, monolith) of the final hydrogen storage material.

Example 6

[0546] NaMn(CO).sub.5 (50.0 g, 229.5 mmol) (prepared by Na reduction of Mn.sub.2(CO).sub.10 in THF) is added dropwise in 500 mL THF at 25° C. to 34.6 g (229.5 mmol) of (CH.sub.3).sub.3SiCH.sub.2COCl in 1000 mL THF (see Organometallics, 13, 5013-5020, 1994). (CO).sub.5Mn(COR) is in equilibrium under CO with (CO).sub.5MnR, which can also be made directly from (CO).sub.5MnNa and R—SO.sub.3CF.sub.3. The solution is then filtered to remove NaCl and the THF is removed in vacuo. 1,3,5-mesitylene (500 mL) is then added and the solution heated by slowly raising the temperature from 100-150° C. under a flow of Ar until a black solid begins to form. The solution is heated overnight at 100-150° C. under Ar and cooled to room temperature. The dark grey solid is collected by filtration and dried in vacuo to afford a black solid, which shows substantial hydrocarbon remaining by Infra Red spectroscopy. The product is then hydrogenated in the solid state or in a supercritical solvent (e.g., supercritical Xe, supercritical Kr, supercritical CO.sub.2, or any combination thereof) to afford the hydrogen storage material.

Example 7

[0547] A mixture of 50 g of bis(trimethylsilylmethyl) manganese and 200 mg Mn.sub.2(CO).sub.10 is placed in a high-pressure reactor equipped with a stirrer. The reaction vessel is then pressurized to 50 bar with high purity CH.sub.4 (N5.0=99.999%) and heated to 100° C. The vessel is then further pressurized to 100 bar and the supercritical solution stirred for 24 hours. Cooling the vessel and depressurization affords a dark grey solid, which shows a CO stretch and substantial hydrocarbon remaining by Infra Red spectroscopy. This species is then hydrogenated in pure H.sub.2 or H.sub.2 dissolved in supercritical CH.sub.4 to yield the final hydrogen storage material.

Example 8

[0548] 50 g of bis(trimethylsilylmethyl) manganese is placed in a high-pressure reactor equipped with a stirrer. The reaction vessel is then pressurized to 50 bar with high purity CH.sub.4 (N5.0=99.999%) and heated to 100° C. The vessel is then further pressurized to 100 bar and the supercritical solution stirred for 24 hours. Cooling the vessel and depressurization affords a dark grey solid, which shows substantial hydrocarbon remaining by Infra Red spectroscopy. This species is then hydrogenated in pure H.sub.2 (with 0.0025 mol CO added by syringe) or a supercritical methane/H.sub.2 mixture (with 0.025 mol CO added by syringe) to yield the final hydrogen storage material, which shows CO incorporation by IR.

[0549] The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and the accompanying figures. Such modifications are intended to fall within the scope of the appended claims.

[0550] Patents, patent applications, publications, product descriptions, and protocols are cited throughout this application, the disclosures of which are incorporated herein by reference in their entireties for all purposes.