Showing papers on "Hydrogen storage published in 2003"

Hydrogen Storage in Microporous Metal-Organic Frameworks

Abstract: Metal-organic framework-5 (MOF-5) of composition Zn4O(BDC)3 (BDC = 1,4-benzenedicarboxylate) with a cubic three-dimensional extended porous structure adsorbed hydrogen up to 4.5 weight percent (17.2 hydrogen molecules per formula unit) at 78 kelvin and 1.0 weight percent at room temperature and pressure of 20 bar. Inelastic neutron scattering spectroscopy of the rotational transitions of the adsorbed hydrogen molecules indicates the presence of two well-defined binding sites (termed I and II), which we associate with hydrogen binding to zinc and the BDC linker, respectively. Preliminary studies on topologically similar isoreticular metal-organic framework-6 and -8 (IRMOF-6 and -8) having cyclobutylbenzene and naphthalene linkers, respectively, gave approximately double and quadruple (2.0 weight percent) the uptake found for MOF-5 at room temperature and 10 bar.

Handbook of fuel cells : fundamentals technology and applications

Abstract: VOLUME 1: FUNDAMENTALS AND SURVEY OF SYSTEMS. Contributors to Volume 1. Foreword. Preface. Abbreviations and Acronyms. Part 1: Thermodynamics and kinetics of fuel cell reactions. Part 2: Mass transfer in fuel cells. Part 3: Heat transfer in fuel cells. Part 4: Fuel cell principles, systems and applications. Contents for Volumes 2, 3 and 4. Subject Index. VOLUME 2: ELECTROCATALYSIS. Contributors to Volume 2. Foreword. Preface. Abbreviations and Acronyms. Part 1: Introduction. Part 2: Theory of electrocatalysis. Part 3: Methods in electrocatalysis. Part 4: The hydrogen oxidation/evolution reaction. Part 5: The oxygen reduction/evolution reaction. Part 6: Oxidation of small organic molecules. Part 7: Other energy conversion related topics. Contents for Volumes 1, 3 and 4. Subject Index. VOLUME 3: FUEL CELL TECHNOLOGY AND APPLICATIONS: PART 1. Contributors to Volumes 3 and 4. Foreword. Preface. Abbreviations and Acronyms. Part 1: Sustainable energy supply. Part 2: Hydrogen storage and hydrogen generation. Development prospects for hydrogen storage. Chemical hydrogen storage devices. Reforming of methanol and fuel processor development. Fuel processing from hydrocarbons to hydrogen. Well-to-wheel efficiencies. Hydrogen safety, codes and standards. Part 3: Polymer electrolyte membrane fuel cell systems (PEMFC). Bipolar plate materials and flow field design. Membrane materials. Electro-catalysts. Membrane-electrode-assembly (MEA). State-of-the-art performance and durability. VOLUME 4: FUEL CELL TECHNOLOGY AND APPLICATIONS, PART 2. Contributors to Volume 3 and 4. Foreword. Preface. Abbreviations and Acronyms. Part 3: Polymer electrolyte membrane fuel cells and systems (PEMFC) (Continued from previous volume). System design and system-specific aspects. Air-supply components. Applications based on PEM-technology. Part 4: Alkaline fuel cells and systems (AFC). Part 5: Phosphoric acid fuel cells and systems (PAFC). Part 6: Direct methanol fuel cells and systems (DMFC). Part 7: Molten carbonate fuel cells and systems (MCFC). Part 8: Solid oxide fuel cells and systems (SOFC). Materials. Stack and system design. New concepts. Part 9: Primary and secondary metal/air cells. Part 10: Portable fuel cell systems. Part 11: Current fuel cell propulsion systems. PEM fuel cell systems for cars/buses. PEM fuel cell systems for submarines. AFC fuel cell systems. Part 12: Electric utility fuel cell systems. Part 13: Future prospects of fuel cell systems. Contents for Volumes 1 and 2. Subject Index.

Theoretical evaluation of hydrogen storage capacity in pure carbon nanostructures

Abstract: Carbon nanotubes have been proposed as promising hydrogen storage materials for the automotive industry. By theoretical analyses and total-energy density functional theory calculations, we show that contribution from physisorption in nanotubes, though significant at liquid nitrogen temperature, should be negligible at room temperature; contribution from chemisorption has a theoretical upper limit of 7.7 wt %, but could be difficult to utilize in practice due to slow kinetics. The metallicity of carbon nanotube is lost at full hydrogen coverage, and we find strong covalent C–H bonding that would slow down the H2 recombination kinetics during desorption. When compared to other pure carbon nanostructures, we find no rational reason yet why carbon nanotubes should be superior in either binding energies or adsorption/desorption kinetics.

Hydrogen storage in carbon nanotubes.

Abstract: The article gives a comprehensive overview of hydrogen storage in carbon nanostructures, including experimental results and theoretical calculations Soon after the discovery of carbon nanotubes in 1991, different research groups succeeded in filling carbon nanotubes with some elements, and, therefore, the question arose of filling carbon nanotubes with hydrogen by possibly using new effects such as nano-capillarity Subsequently, very promising experiments claiming high hydrogen storage capacities in different carbon nanostructures initiated enormous research activity Hydrogen storage capacities have been reported that exceed the benchmark for automotive application of 65 wt% set by the US Department of Energy However, the experimental data obtained with different methods for various carbon nanostructures show an extreme scatter Classical calculations based on physisorption of hydrogen molecules could not explain the high storage capacities measured at ambient temperature, and, assuming chemisorption of hydrogen atoms, hydrogen release requires temperatures too high for technical applications Up to now, only a few calculations and experiments indicate the possibility of an intermediate binding energy Recently, serious doubt has arisen in relation to several key experiments, causing considerable controversy Furthermore, high hydrogen storage capacities measured for carbon nanofibers did not survive cross-checking in different laboratories Therefore, in light of today's knowledge, it is becoming less likely that at moderate pressures around room temperature carbon nanostructures can store the amount of hydrogen required for automotive applications

Efficient hydrogen production using cyclohexane and decalin by pulse-spray mode reactor with Pt catalysts

Abstract: Highly efficient production of hydrogen without CO 2 emission is achieved in the dehydrogenation of cyclic hydrocarbons under a non-steady spray pulse operation over supported Pt and Pt-M (M=Re, Rh, Pd) catalysts. Cyclohexane, methylcyclohexane, tetralin and decalin were efficiently dehydrogenated by the Pt-containing catalysts supported on thin active carbon cloth (CFF-1500S) sheets and alumite (anodized aluminum) plates. Production rate of hydrogen under the spray pulse mode is higher than the conventional batch-type liquid phase reaction and the steady state gas phase reaction in the flow system. The highest rate, 3800 mmol g Pt −1 min −1 , was obtained in the dehydrogenation of cyclohexane over Pt/alumite heated at 375 °C and cyclohexane feed of 190 mmol min −1 with 3.5 mmol pulse at 1.0 s interval. Bimetallic Pt-Rh/CFF-1500S catalyst showed a higher activity than monometallic Pt/CFF-1500S. Production rate of hydrogen is greatly dependent on the rate of reactant feed, the reaction temperature, and the support. Retardation by products adsorbed on the catalysts was negligible under the spray-pulse operation.

Dehydrogenation of TiH2

Abstract: Hydrogen is a unique alloying element for titanium because it can be introduced into the metal to form solid solutions or stoichiometric compounds by exposure to the gas at elevated temperatures and removed by vacuum annealing Studies on dehydrogenation of fine titanium hydride are important for several applications such as thermohydrogen processing of Ti and Ti based alloy components, hydrogen storage materials and bonding of metals and ceramics using TiH2 Effect of particle size on dehydrogenation of TiH2 is studied here, using thermal analysis along with structural investigations Dehydrogenation of nanocrystalline hydride powder differs considerably from the micron size starting powder A two step dehydrogenation process, (TiH2 → TiHx → α-Ti) where 07

Titanium disulfide nanotubes as hydrogen-storage materials.

Abstract: TiS2 nanotubes, which were synthesized through a chemical transport reaction, are very effective in reversible hydrogen absorption and desorption with the capacity of 25 wt %

Hydrogen adsorption in carbon nanostructures: comparison of nanotubes, fibers, and coals.

Abstract: Single-walled carbon nano- tubes (SWNT) were reported to have record high hydrogen storage capacities at room temperature, indicating an in- teraction between hydrogen and carbon matrix that is stronger than known before.Here we present a study of the interaction of hydrogen with activated charcoal, carbon nanofibers, and SWNT that disproves these earlier reports.The hydrogen storage capacity of these ma- terials correlates with the surface area of the material, the activated charcoal having the largest.The SWNT appear to have a relatively low accessible sur- face area due to bundling of the tubes; the hydrogen does not enter the voids between the tubes in the bundles.Pres- sure ± temperature curves were used to estimate the interaction potential, which was found to be 580 60 K.Hydrogen gas was adsorbed in amounts up to 2 wt % only at low temperatures.Mo- lecular rotations observed with neutron scattering indicate that molecular hy- drogen is present, and no significant difference was found between the hy- drogen molecules adsorbed in the differ- ent investigated materials.Results from density functional calculations show molecular hydrogen bonding to an ar- omatic CC bond that is present in the materials investigated.The claims of high storage capacities of SWNT related to their characteristic morphology are unjustified.

Hydrogen storage capacity of commercially available carbon materials at room temperature

Abstract: The hydrogen storage capacity of five types of commercially available carbon materials with different nanostructures was measured at up to 8 MPa at room temperature using an apparatus based on a volumetric method with an error of less than 0.04 wt %/gr. The highest storage capacity of 0.43 wt % was obtained for purified HiPco™ single-walled carbon nanotubes (SWNTs). In the SWNTs, the hydrogen density in pores with a diameter of less than 1 nm was estimated to be a 0.022 g/ml, which corresponds to 31% of the density of liquid hydrogen. Issues in the development of carbon-based hydrogen storage media are discussed.

Hydrogen storage in carbon nanotubes and related materials

Abstract: Adsorption of hydrogen at 300 K has been investigated on well-characterized samples of carbon nanotubes, besides carbon fibres by taking care to avoid many of the pitfalls generally encountered in such measurements. The nanotube samples include single- and multi-walled nanotubes prepared by different methods, as well as aligned bundles of multi-walled nanotubes. The effect of acid treatment of the nanotubes has been examined. A maximum adsorption of ca. 3.7 wt% is found with aligned multi-walled nanotubes. Electrochemical hydrogen storage measurements have also been carried out on the nanotube samples and the results are similar to those found by gas adsorption measurements.

Mass sensing of adsorbed molecules in sub-picogram sample with ultrathin silicon resonator

Abstract: Ultrathin single-crystalline silicon cantilevers with a thickness of 170 nm as a resonating sensor are applied to mass sensing. The hydrogen storage capacity of a small amount of carbon nanotubes (CNTs), which were mounted on an ultrathin resonator by a manipulator, is measured from the resonant frequency change. The resonator is annealed in ultrahigh vacuum to clean the surface and increase the quality factor, and exposed to oxygen gas to oxidize the surface for long-term stability. The resonator can be electrostatically actuated, and the vibration is measured by a laser Doppler vibrometer in ultrahigh vacuum. The mass of the CNTs is determined by the difference of resonant frequencies before and after mounting the CNTs, and the hydrogen storage capacity is determined from the frequency change after exposure to high-pressure hydrogen as well. The obtained hydrogen storage capacitance is 1.6%–6.0%. The available mass resolution and the achieved stability of the resonance of the 170-nm-thick resonator are below 10−18 g and 5 Hz/days, respectively.