Showing papers on "Hydrogen storage published in 2005"

Strategies for hydrogen storage in metal--organic frameworks.

Abstract: Increased attention is being focused on metal-organic frameworks as candidates for hydrogen storage materials. This is a result of their many favorable attributes, such as high porosity, reproducible and facile syntheses, amenability to scale-up, and chemical modification for targeting desired properties. A discussion of several strategies aimed at improving hydrogen uptake in these materials is presented. These strategies include the optimization of pore size and adsorption energy by linker modification, impregnation, catenation, and the inclusion of open metal sites and lighter metals.

Complex Hydrides for Hydrogen Storage

Abstract: Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Reversible storage of hydrogen in destabilized LiBH4.

Abstract: Destabilization of LiBH4 for reversible hydrogen storage has been studied using MgH2 as a destabilizing additive. Mechanically milled mixtures of LiBH4 + 1/2MgH2 or LiH + 1/2MgB2 including 2−3 mol % TiCl3 are shown to reversibly store 8−10 wt % hydrogen. Variation of the equilibrium pressure obtained from isotherms measured at 315−400 °C indicate that addition of MgH2 lowers the hydrogenation/dehydrogenation enthalpy by 25 kJ/(mol of H2) compared with pure LiBH4. Formation of MgB2 upon dehydrogenation stabilizes the dehydrogenated state and, thereby, destabilizes the LiBH4. Extrapolation of the isotherm data yields a predicted equilibrium pressure of 1 bar at approximately 225 °C. However, the kinetics were too slow for direct measurements at these temperatures.

Titanium-decorated carbon nanotubes as a potential high-capacity hydrogen storage medium.

Abstract: We report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H2 adsorption is dissociative with no energy barrier while the other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8 wt % hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.

Nanoscaffold Mediates Hydrogen Release and the Reactivity of Ammonia Borane

Abstract: One of the imposing barriers to realizing the promise of an energy economy based on hydrogen is onboard hydrogen storage for fuel-cell-powered vehicles. New materials that enable the release of dense, plentiful and pure hydrogen at temperatures less than 85 oC are necessary to move the world from an oil-based economy to a hydrogen economy. We report a novel approach in which we deposit a hydrogen-rich material into a nanoporous scaffold. The role of the scaffold is to impose a nano-phase structure on the hydrogen-rich material thus providing an additional handle on the kinetics and thermodynamics of hydrogen release. We demonstrate on the example of ammonia borane infused in the nanoporous silica that the kinetics of hydrogen release is improved while the purity of hydrogen is increased in comparison with the release from bulk ammonia borane. These findings suggest that hydrogen rich materials infused in nanoscaffolds offer the most promising approach to date for onboard hydrogen storage

Tuning clathrate hydrates for hydrogen storage

Abstract: The storage of large quantities of hydrogen at safe pressures is a key factor in establishing a hydrogen-based economy. Previous strategies--where hydrogen has been bound chemically, adsorbed in materials with permanent void space or stored in hybrid materials that combine these elements--have problems arising from either technical considerations or materials cost. A recently reported clathrate hydrate of hydrogen exhibiting two different-sized cages does seem to meet the necessary storage requirements; however, the extreme pressures (approximately 2 kbar) required to produce the material make it impractical. The synthesis pressure can be decreased by filling the larger cavity with tetrahydrofuran (THF) to stabilize the material, but the potential storage capacity of the material is compromised with this approach. Here we report that hydrogen storage capacities in THF-containing binary-clathrate hydrates can be increased to approximately 4 wt% at modest pressures by tuning their composition to allow the hydrogen guests to enter both the larger and the smaller cages, while retaining low-pressure stability. The tuning mechanism is quite general and convenient, using water-soluble hydrate promoters and various small gaseous guests.

Clustering of Ti on a C60 surface and its effect on hydrogen storage

Abstract: Recent efforts in finding materials suitable for storing hydrogen with large gravimetric density have focused attention on carbon-based nanostructures. Unfortunately, pure carbon nanotubes and fullerenes are unsuitable as hydrogen storage materials because of the weak bonding of the hydrogen molecules to the carbon frame. It has been shown very recently that coating of carbon nanostructures with isolated transition metal atoms such as Sc and Ti can increase the binding energy of hydrogen and lead to high storage capacity (up to 8 wt % hydrogen, which is 1.6 times the U.S. Department of Energy target set for 2005). This prediction has led to a great deal of excitement in the fuel cell community [see The Fuel Cell Review, http://fcr.iop.org/articles/features/2/7/4]. However, this prediction depends on the assumption that the metal atoms coated on the fullerene surface will remain isolated. Using first-principles calculations based on density functional theory, we show that Ti atoms would prefer to cluster on the C60 surface, which can significantly alter the nature of hydrogen bonding, thus affecting not only the amount of stored hydrogen but also their thermodynamics and kinetics.

Graphene nanostructures as tunable storage media for molecular hydrogen

Abstract: Many methods have been proposed for efficient storage of molecular hydrogen for fuel cell applications. However, despite intense research efforts, the twin U.S. Department of Energy goals of 6.5% mass ratio and 62 kg/m3 volume density has not been achieved either experimentally or via theoretical simulations on reversible model systems. Carbon-based materials, such as carbon nanotubes, have always been regarded as the most attractive physisorption substrates for the storage of hydrogen. Theoretical studies on various model graphitic systems, however, failed to reach the elusive goal. Here, we show that insufficiently accurate carbon–H2 interaction potentials, together with the neglect and incomplete treatment of the quantum effects in previous theoretical investigations, led to misleading conclusions for the absorption capacity. A proper account of the contribution of quantum effects to the free energy and the equilibrium constant for hydrogen adsorption suggest that the U.S. Department of Energy specification can be approached in a graphite-based physisorption system. The theoretical prediction can be realized by optimizing the structures of nano-graphite platelets (graphene), which are light-weight, cheap, chemically inert, and environmentally benign.

Hydrogen storage in magnesium clusters: quantum chemical study.

Abstract: Magnesium hydride is cheap and contains 7.7 wt % hydrogen, making it one of the most attractive hydrogen storage materials. However, thermodynamics dictate that hydrogen desorption from bulk magnesium hydride only takes place at or above 300 °C, which is a major impediment for practical application. A few results in the literature, related to disordered materials and very thin layers, indicate that lower desorption temperatures are possible. We systematically investigated the effect of crystal grain size on the thermodynamic stability of magnesium and magnesium hydride, using ab initio Hartree−Fock and density functional theory calculations. Also, the stepwise desorption of hydrogen was followed in detail. As expected, both magnesium and magnesium hydride become less stable with decreasing cluster size, notably for clusters smaller than 20 magnesium atoms. However, magnesium hydride destabilizes more strongly than magnesium. As a result, the hydrogen desorption energy decreases significantly when the crys...

Catalytic effect of nanoparticle 3d-transition metals on hydrogen storage properties in magnesium hydride MgH2 prepared by mechanical milling.

Abstract: We examined the catalytic effect of nanoparticle 3d-transition metals on hydrogen desorption (HD) properties of MgH(2) prepared by mechanical ball milling method. All the MgH(2) composites prepared by adding a small amount of nanoparticle Fe(nano), Co(nano), Ni(nano), and Cu(nano) metals and by ball milling for 2 h showed much better HD properties than the pure ball-milled MgH(2) itself. In particular, the 2 mol % Ni(nano)-doped MgH(2) composite prepared by soft milling for a short milling time of 15 min under a slow milling revolution speed of 200 rpm shows the most superior hydrogen storage properties: A large amount of hydrogen ( approximately 6.5 wt %) is desorbed in the temperature range from 150 to 250 degrees C at a heating rate of 5 degrees C/min under He gas flow with no partial pressure of hydrogen. The EDX micrographs corresponding to Mg and Ni elemental profiles indicated that nanoparticle Ni metals as catalyst homogeneously dispersed on the surface of MgH(2). In addition, it was confirmed that the product revealed good reversible hydriding/dehydriding cycles even at 150 degrees C. The hydrogen desorption kinetics of catalyzed and noncatalyzed MgH(2) could be understood by a modified first-order reaction model, in which the surface condition was taken into account.

Progress and problems in hydrogen storage methods

Abstract: A technique of hydrogen storage has to meet the DOE criterion for the volumetric and gravimetric density of the stored hydrogen and the reversibility criterion for the charging/discharging processes. There are basically five candidate methods that have attracted the common interest: compression, liquefaction, physisorption, metallic hydrides, and complex hydrides. An overview was given for the storage methods available today with respect to the progress made recently and problems still there.

Adsorption of Gases in Metal Organic Materials: Comparison of Simulations and Experiments

Abstract: Molecular simulations using standard force fields have been carried out to model the adsorption of various light gases on a number of different metal organic framework-type materials. The results have been compared with the available experimental data to test the validity of the model potentials. We observe good agreement between simulations and experiments for a number of different cases and very poor agreement in other cases. Possible reasons for the discrepancy in simulated and measured isotherms are discussed. We predict hydrogen adsorption isotherms at 77 and 298 K in a number of different metal organic framework materials. The importance of quantum diffraction effects and framework charges on the adsorption of hydrogen at 77 K is discussed. Our calculations indicate that at room temperature none of the materials that we have tested is able to meet the requirements for on-board hydrogen storage for fuel cell vehicles. We have calculated the volume available in a given sorbent at a specified adsorption energy (density of states). We discuss how this density of states can be used to assess the effectiveness of a sorbent material for hydrogen storage.

Hydrogen desorption exceeding ten weight percent from the new quaternary hydride Li3BN2H8.

Abstract: Mobile applications of hydrogen power have long demanded new solid hydride materials with large hydrogen storage capacities. We report synthesis of a new quaternary hydride having the approximate composition Li(3)BN(2)H(8) with 11.9 wt % theoretical hydrogen capacity. It forms by reacting LiNH(2) and LiBH(4) powders in a 2:1 molar ratio either by ball milling or by heating the mixed powders above 95 degrees C. This new quaternary hydride melts at approximately 190 degrees C and releases > or =10 wt % hydrogen above approximately 250 degrees C. A small amount of ammonia (2-3 mol % of the generated gas) is released simultaneously. Preliminary calorimetric measurements suggest that hydrogen release is exothermic and, hence, not easily reversible.

Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage.

Abstract: The poor performance of hydrogen storage materials continues to hinder development of fuel cell-powered automobiles. Nanoscale carbons, in particular (activated carbon, exfoliated graphite, fullerenes, nanotubes, nanofibers, and nanohorns), have not fulfilled their initial promise. Here we show that carbon materials can be rationally designed for H2 storage. Carbide-derived carbons (CDC), a largely unknown class of porous carbons, are produced by high-temperature chlorination of carbides. Metals and metalloids are removed as chlorides, leaving behind a collapsed noncrystalline carbon with up to 80% open pore volume. The detailed nature of the porosity-average size and size distribution, shape, and total specific surface area (SSA)-can be tuned with high sensitivity by selection of precursor carbide (composition, lattice type) and chlorination temperature. The optimum temperature is bounded from below by thermodynamics and kinetics of chlorination reactions and from above by graphitization, which decreases SSA and introduces H2-sorbing surfaces with binding energies too low to be useful. Intuitively, pores of different size and shape should not contribute equally to hydrogen storage. By correlating pore properties with 77 K H2 isotherms from a wide variety of CDCs, we experimentally confirm that gravimetric hydrogen storage capacity normalized to total pore volume is optimized in materials with primarily micropores ( approximately 1 nm) rather than mesopores. Thus, in agreement with theoretical predictions, a narrow size distribution of small pores is desirable for storing hydrogen, while large pores merely degrade the volumetric storage capacity.

Hydrogen storage in nanostructured carbons by spillover: bridge-building enhancement.

Abstract: The hydrogen storage capacity in nanostructured carbon materials can be increased by atomic hydrogen spillover from a supported catalyst. A simple and effective technique was developed to build carbon bridges that serve to improve contact between a spillover source and a secondary receptor. In this work, a supported catalyst (Pd-C) served as the source of hydrogen atoms via dissociation and primary spillover and AX-21 or single-walled carbon nanotubes (SWNTs) were secondary spillover receptors. By carbonizing a bridge-forming precursor in the presence of the components, the hydrogen adsorption amount was increased by a factor of 2.9 for the AX-21 receptor and 1.6 for the SWNT receptor at 298 K and 100 kPa. Similar results were obtained at 10 MPa, indicating that the enhancement factor is a weak function of pressure. The AX-21 receptor with carbon bridges had the highest absolute capacity of 1.8 wt % at 298 K and 10 MPa. Reversibility was demonstrated through desorption and readsorption at 298 K. The bridge-building process appears to be receptor specific, and optimization may yield even greater enhancement. Using this technique, enhancements in storage of up to 17-fold on other carbon-based materials have been observed and will be reported elsewhere shortly.

Beyond Oil and Gas: The Methanol Economy

Abstract: Chapter 1: Introduction. Chapter 2: Coal in the Industrial Revolution, and Beyond. Chapter 3: History of Oil and Natural Gas. Oil Extraction and Exploration. Natural Gas. Chapter 4: Fossil Fuel Resources and Uses. Coal. Oil. Tar Sands. Oil Shale. Natural Gas. Coalbed Methane. Tight Sands and Shales. Methane Hydrates. Outlook. Chapter 5: Diminishing Oil and Gas Reserves. Chapter 6: The Continuing Need for Hydrocarbons and their Products. Fractional Distillation. Thermal Cracking. Chapter 7: Fossil Fuels and Climate Change. Mitigation. Chapter 8: Renewable Energy Sources and Atomic Energy. Hydropower. Geothermal Energy. Wind Energy. Solar Energy: Photovoltaic and Thermal. Electricity from Photovoltaic Conversion. Solar Thermal Power for Electricity Production. Electric Power from Saline Solar Ponds. Solar Thermal Energy for Heating. Economic Limitations of Solar Energy. Biomass Energy. Electricity from Biomass. Liquid Biofuels. Ocean Energy: Thermal, Tidal, and Wave Power. Tidal Energy. Waves. Ocean Thermal Energy. Nuclear Energy. Energy from Nuclear Fission Reactions. Breeder Reactors. The Need for Nuclear Power. Economics. Safety. Radiation Hazards. Nuclear Byproducts and Waste. Emissions. Nuclear Power: An Energy Source for the Future. Nuclear Fusion. Future Outlook. Chapter 9: The Hydrogen Economy and its Limitations. The Discovery and Properties of Hydrogen. The Development of Hydrogen Energy. The Production and Uses of Hydrogen. Hydrogen from Fossil Fuels. Hydrogen from Biomass. Photobiological Water Cleavage. Water Electrolysis. Hydrogen Production Using Nuclear Energy. The Challenge of Hydrogen Storage. Liquid Hydrogen. Compressed Hydrogen. Metal Hydrides and Solid Absorbents. Other Means of Hydrogen Storage. Hydrogen: Centralized or Decentralized Distribution? Safety of Hydrogen. Hydrogen in Transportation. Fuel Cells. History. Fuel Cell Efficiency. Hydrogen-Based Fuel Cells. PEM Fuel Cells for Transportation. Regenerative Fuel Cells. Outlook. Chapter 10: The "Methanol Economy": General Aspects. Chapter 11: Methanol as a Fuel and Energy Carrier. Properties and Historical Background. Present Uses of Methanol. Use of Methanol and Dimethyl Ether as Transportation Fuels. Alcohol as a Transportation Fuel in the Past. Methanol as Fuel in Internal Combustion Engines (ICE). Methanol and Dimethyl Ether as Diesel Fuels Substitute in Compression Ignition Engines. Biodiesel Fuel. Advanced Methanol-Powered Vehicles. Hydrogen for Fuel Cells from Methanol Reforming. Direct Methanol Fuel Cell (DMFC). Fuel Cells Based on Other Fuels and Biofuel Cells. Regenerative Fuel Cell. Methanol for Static Power and Heat Generation. Methanol Storage and Distribution. Methanol Price. Methanol Safety. Emissions from Methanol-Powered Vehicles. Methanol and the Environment. Methanol and Issues of Climate Change. Chapter 12: Production of Methanol from Syn-Gas to Carbon Dioxide. Methanol from Fossil Fuels. Production via Syn-Gas. Syn-Gas from Natural Gas. Methane Steam Reforming. Partial Oxidation of Methane. Autothermal Reforming and Combination of Steam Reforming and Partial Oxidation. Syn-Gas from CO2 Reforming. Syn-Gas from Petroleum and Higher Hydrocarbons. Syn-Gas from Coal. Economics of Syn-Gas Generation. Methanol through Methyl Formate. Methanol from Methane Without Syn-Gas. Selective Oxidation of Methane to Methanol. Catalytic Gas-Phase Oxidation of Methane. Liquid-Phase Oxidation of Methane to Methanol. Methanol Production through Mono-Halogenated Methanes. Microbial or Photochemical Conversion of Methane to Methanol. Methanol from Biomass. Methanol from Biogas. Aquaculture. Water Plants. Algae. Methanol from Carbon Dioxide. Carbon Dioxide from Industrial Flue Gases. Carbon Dioxide from the Atmosphere. Chapter 13: Methanol-Based Chemicals, Synthetic Hydrocarbons and Materials. Methanol-Based Chemical Products and Materials. Methanol Conversion to Olefins and Synthetic Hydrocarbons. Methanol to Olefin (MTO) Process. Methanol to Gasoline (MTG) Process. Methanol-Based Proteins. Outlook. Chapter 14: Future Perspectives. The "Methanol Economy" and its Advantages. Further Reading and Information. References. Index.

Hydrogen storage in ni nanoparticle-dispersed multiwalled carbon nanotubes.

Abstract: Hydrogen storage properties of mutiwalled carbon nanotubes (MWCNTs) with Ni nanoparticles were investigated. The metal nanoparticles were dispersed on MWCNTs surfaces using an incipient wetness impregnation procedure. Ni catalysts have been known to effectively dissociate hydrogen molecules in gas phase, providing atomic hydrogen possible to form chemical bonding with the surfaces of MWCNTs. Hydrogen desorption spectra of MWCNTs with 6 wt % of Ni nanoparticles showed that ∼2.8 wt % hydrogen was released in the range of 340−520 K. In Kissinger's plot to evaluate the nature of interaction between hydrogen and MWCNTs with Ni nanoparticles, the hydrogen desorption activation energy was measured to be as high as ∼31 kJ/mol·H2, which is much higher than the estimates of pristine SWNTs. C−Hn stretching vibrations after hydrogenation in FTIR further supported that hydrogen molecules were dissociated when bound to the surfaces of MWCNTs. During cyclic hydrogen absorption/desorption, there was observed no significa...

Molecular Simulation of Adsorption and Diffusion of Hydrogen in Metal−Organic Frameworks

Abstract: Metal-organic frameworks (MOFs) are thought to be a set of promising hydrogen storage materials; however, little is known about the interactions between hydrogen molecules and pore walls as well as the diffusivities of hydrogen in MOFs. In this work, we performed a systematic molecular simulation study on the adsorption and diffusion of hydrogen in MOFs to provide insight into molecular-level details of the underlying mechanisms. This work shows that metal-oxygen clusters are preferential adsorption sites for hydrogen in MOFs, and the effect of the organic linkers becomes evident with increasing pressure. The hydrogen storage capacity of MOFs is similar to carbon nanotubes, which is higher than zeolites. Diffusion of hydrogen in MOFs is an activated process that is similar to diffusion in zeolites. The information derived in this work is useful to guide the future rational design and synthesis of tailored MOF materials with improved hydrogen adsorption capability.

Adsorption and dissociation of hydrogen molecules on bare and functionalized carbon nanotubes

Abstract: Interaction between hydrogen molecules and bare as well as functionalized single-wall carbon nanotubes SWNT is investigated using first-principles plane wave method. It is found that the binding energy of the H2 physisorbed on the outer surface of the bare SWNT is very weak, and cannot be enhanced significantly either by increasing the curvature of the surface through radial deformation, or by the coadsorption of a Li atom that makes the semiconducting tube metallic. Although the bonding is strengthened upon adsorption directly to the Li atom, its nature continues to be physisorption. However, the character of the bonding changes dramatically when SWNT is functionalized by the adsorption of a Pt atom. A single H2 is chemisorbed to the Pt atom on the SWNT either dissociatively or molecularly. The dissociative adsorption is favorable energetically and is followed by the weakening of the Pt-SWNT bond. Out of two adsorbed H2, the first one can be adsorbed dissociatively and the second one is chemisorbed molecularly. The nature of bonding is a very weak physisorption for the third adsorbed H2. Palladium also promotes the chemisorption of H2 with relatively smaller binding energy. Present results reveal the important effect of transition metal atom adsorbed on SWNT and these results advance our understanding of the molecular and dissociative adsorption of hydrogen for efficient hydrogen storage.

Enhancement of hydrogen physisorption on graphene and carbon nanotubes by Li doping

Abstract: Density-functional calculations of the adsorption of molecular hydrogen on a planar graphene layer and on the external surface of a (4,4) carbon nanotube, undoped and doped with lithium, have been carried out. Hydrogen molecules are physisorbed on pure graphene and on the nanotube with binding energies about 80-90 meV/molecule. However, the binding energies increase to 160-180 meV/molecule for many adsorption configurations of the molecule near a Li atom in the doped systems. A charge-density analysis shows that the origin of the increase in binding energy is the electronic charge transfer from the Li atom to graphene and the nanotube. The results support and explain qualitatively the enhancement of the hydrogen storage capacity observed in some experiments of hydrogen adsorption on carbon nanotubes doped with alkali atoms.

Hydrogen Cycling of Niobium and Vanadium Catalyzed Nanostructured Magnesium

Abstract: The reaction of hydrogen gas with magnesium metal, which is important for hydrogen storage purposes, is enhanced significantly by the addition of catalysts such as Nb and V and by using nanostructured powders. In situ neutron diffraction on MgNb0.05 and MgV0.05 powders give a detailed insight on the magnesium and catalyst phases that exist during the various stages of hydrogen cycling. During the early stage of hydriding (and deuteriding), a MgH1

Hydrogen adsorption on functionalized nanoporous activated carbons

Abstract: There is considerable interest in hydrogen adsorption on carbon nanotubes and porous carbons as a method of storage for transport and related energy applications. This investigation has involved a systematic investigation of the role of functional groups and porous structure characteristics in determining the hydrogen adsorption characteristics of porous carbons. Suites of carbons were prepared with a wide range of nitrogen and oxygen contents and types of functional groups to investigate their effect on hydrogen adsorption. The porous structures of the carbons were characterized by nitrogen (77 K) and carbon dioxide (273 K) adsorption methods. Hydrogen adsorption isotherms were studied at 77 K and pressure up to 100 kPa. All the isotherms were Type I in the IUPAC classification scheme. Hydrogen isobars indicated that the adsorption of hydrogen is very temperature dependent with little or no hydrogen adsorption above 195 K. The isosteric enthalpies of adsorption at zero surface coverage were obtained using a virial equation, while the values at various surface coverages were obtained from the van't Hoff isochore. The values were in the range 3.9-5.2 kJ mol(-1) for the carbons studied. The thermodynamics of the adsorption process are discussed in relation to temperature limitations for hydrogen storage applications. The maximum amounts of hydrogen adsorbed correlated with the micropore volume obtained from extrapolation of the Dubinin-Radushkevich equation for carbon dioxide adsorption. Functional groups have a small detrimental effect on hydrogen adsorption, and this is related to decreased adsorbate-adsorbent and increased adsorbate-adsorbate interactions.

Liquid hydrogen in protonic chabazite.

Abstract: Due to its fully reversible nature, H2 storage by molecular adsorption could represent an advantage with respect to dissociative processes, where kinetic effects during the charging and discharging processes are present. A drawback of this strategy is represented by the extremely weak interactions that require low temperature and high pressure. High surface area materials hosting polarizing sites can represent a viable way toward more favorable working conditions. Of these, in this contribution, we have studied hydrogen adsorption in a series of zeolites using volumetric techniques and infrared spectroscopy at 15 K. We have found that in H-SSZ-13 zeolite the cooperative role played by high surface area, internal wall topology, and presence of high binding energy sites (protons) allows hydrogen to densify inside the nanopores at favorable temperature and pressure conditions.