Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H16: Focus Session: Hydrogen Storage II |
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Sponsoring Units: FIAP Chair: Gregory P. Meisner, General Motors Room: Baltimore Convention Center 312 |
Tuesday, March 14, 2006 11:15AM - 11:27AM |
H16.00001: Infrared Spectroscopy of Hydrogen in Fullerite and MOF-5 Hosts Stephen FitzGerald, Hugh Churchill, Phil Korngut, Christie Simmons, Yorgos Strangas We present a novel use of diffuse reflectance infrared spectroscopy to study the quantum dynamics of hydrogen molecules trapped within a host material. This technique is particularly useful for the study of hydrogen storage materials since it provides detailed information about the intermolecular potential at the binding site. Because H$_{2}$ has no intrinsic infrared activity any observed features arise solely through interaction with the host material and as such are very sensitive to the symmetry of the binding site. The drawback is that the induced spectra are quite weak. However, a technique based on diffuse reflectance has been shown to produce a sufficiently large signal [1]. We have now constructed a cryogenic system that allows spectra to be obtained in this manner at pressures as high as 100 atm. and at temperatures as low as 10 K. Data will be presented for H$_{2}$ in both C$_{60} $ and MOF-5 showing a series of absorption features arising from the quantized vibrational, rotational, and translational motion of the trapped H$_{2}$. At the lowest temperature these peaks become quite sharp, FWHM less than 1 cm$^{-1}$, with a detailed fine structure arising from the H$_{2}$ host interactions. \\ 1. S. A. FitzGerald et al., Phys. Rev. B {\bf 65}, 140302. (2002) [Preview Abstract] |
Tuesday, March 14, 2006 11:27AM - 11:39AM |
H16.00002: Hydrogen Adsorption and Its Displacement of Carbon Dioxide in Microporous Transition Metal Cyanides Sittichai Natesakhawat, Jeffrey Culp, Christopher Matranga, Bradley Bockrath The adsorption properties of H$_{2}$ and CO$_{2}$ have been investigated in M$_{3}$[Co(CN)$_{6}$] (M = Cu, Zn) Prussian blue analogues and M[Fe(CN)$_{5}$NO] (M= Co, Ni) metal nitroprussides. Adsorption isotherms show that both materials adsorb between 1.4 to 1.7 wt {\%} of H$_{2}$ at 77 K and 1 atm. The isosteric heat of adsorption was between 6.5 to 7.5 kJ/mol. Kinetic measurements are conducted in a specially designed vacuum system which is coupled to a Fourier-Transform Infrared Spectrometer. In a typical experiment, an infrared active gas (i.e CO$_{2})$ is physisorbed in the transition metal cyanide and the system is later back-filled with H$_{2}$. The infrared intensity of the physisorbed CO$_{2}$ is monitored to deduce the kinetics and energetics associated with its displacement from the transition metal cyanide by H$_{2}$. We have identified several kinetic steps, measured the rate constants, and examined the temperature dependence of this displacement process. [Preview Abstract] |
Tuesday, March 14, 2006 11:39AM - 11:51AM |
H16.00003: Adsorption study of Hydrogen in Carbon based Materials as measured by Nuclear Magnetic Resonance Alfred Kleinhammes, Shenghua Mao, Marcelo Behar, Yue Wu Nuclear magnetic resonance is shown to be a sensitive tool to probe hydrogen adsorption. The technique distinguishes between adsorbed H$_{2}$, hydrogen in the gas phase and can discriminate against protons brought in through contaminants. NMR provides a quantitative measurement of the number of molecules adsorbed. An estimate of the adsorption energy can be obtained from the measured isotherm. Adsorption measurements of H$_{2}$ in several materials -- metal organic frameworks, conducting polymers, and doped single walled carbon nanotubes -- are reported. Boron doped SWNTs when loaded with H$_{2}$ produce intriguing $^{1}$Hspectra indicative of adsorption and possibly several adsorption sites [Preview Abstract] |
Tuesday, March 14, 2006 11:51AM - 12:27PM |
H16.00004: Hydrogen cryo-adsorption; comparing low pressure and isosteric heats Invited Speaker: The two criteria for effective physisorbents for hydrogen storage are high surface area and high adsorption heats. There are two heats that can be determined readily from the sorption isotherm. At very low pressures corresponding to low surface coverages, we can consider the differential enthalpy at zero coverage, determined from the temperature dependence of the Henry's Law constant which is in turn determined by the low pressure isotherm slope. The differential enthalpy can also be determined from isosteric heat measurements from the same data, provided that data is taken over a higher pressure range that includes the saturation limit. We have found that the two quantities are of similar magnitude, and while the direct measurement of the differential enthalpy is the easiest to perform, the requirements necessary in determining the isosteric heat yield the most useful data. Ideally, the sorption heats are constant as a function of ad-atom/molecule coverage density. This is typically not the case due to sorption site heterogeneities that are typical of real surfaces, and due to hydrogen-hydrogen interactions that occur at higher pressures. Consequently, this value drops as a function of pressure. The consequence of this is that materials that show initially high sorption values at low pressure, do not typically yield high gravimetric saturation values. We will discuss this behavior in metal organic frameworks, activated carbons and carbon aerogels. All of these materials can have high surface area but the adsorption heats are typically 4--7 kJ/mole. We have measured the highest gravimetric hydrogen sorption in an activated carbon. [Preview Abstract] |
Tuesday, March 14, 2006 12:27PM - 12:39PM |
H16.00005: Inelastic Neutron Scattering of H$_{2}$ Adsorbed on Boron Doped ($\sim $ 1\%) Single Walled Carbon Nanotubes D. Narehood, Y. Liu, C.M. Brown, D.A. Neumann, Peter Eklund It is clear from this study that H$_{2}$ is preferentially adsorbed at boron sites in SWNTs and in these sites the H$_{2}$ experiences an orientational component in the potential. Thus, this study shows that the substitution of boron for carbon in the SWNT lattice produces higher energy binding sites for H$_{2}$ adsorption. We report here an inelastic neutron scattering investigation of H$_{2}$ adsorbed on $\sim $ 200 mg of purified boron doped ($\le $ 1{\%}) SWNT bundles. At H$_{2}$ coverages $\le $ 1 H$_{2}$/ B and at T = 3K, a clear splitting of $\sim $ 1.4 meV is observed for the sublevels of the J=1 state. As the H$_{2}$ coverage is increased, the rotational spectrum converges to that of the bulk like rotor observed for H$_{2}$adsorbed on undoped SWNTs with the appearance of a peak at 14.7 meV. As the temperature is increased from 3K, the bulk like peak decreases in intensity until only the split rotational peaks are present; the intensity of these peaks decreases with increasing temperature until about 75 K at which point no rotational peak is observable. Funding provided by the US DOE Office of Energy Efficiency and Renewable Energy within the Center of Excellence on Carbon-based Hydrogen Storage Materials. [Preview Abstract] |
Tuesday, March 14, 2006 12:39PM - 12:51PM |
H16.00006: Quantum Monte Carlo studies of the non-dissociative absorption of hydrogen to doped fullerenes Andrew Williamson, Yong-Hyun Kim, Shengbai Zhang The reversible storage of hydrogen at room temperature requires an adsorption energy in the range of 0.2 to 0.6 eV per hydrogen molecule. However, there are currently no storage materials which have been shown to bind hydrogen with this energy. Typically, hydrogen either retains its molecular form, and binds only weakly via a van der Waals interaction, or it dissociates into atoms and forms strong covalent bonds. Here we present the results of first-principles density functional and Quantum Monte Carlo calculations of the non-dissociative absorption of hydrogen molecules to doped carbon fullerenes. These calculations reveal significantly enhanced binding of hydrogen to substitutional B and Be doped fullerenes. Our Quantum Monte Carlo and benchmark quantum chemistry calculations are used to evaluate the accuracy of different exchange correlation functionals for describing the hydrogen adsorption interaction. We find that the LDA functional significantly overestimates the binding energy of hydrogen, while GGA functionals underestimate the binding energy. This work was performed under the auspices of the US Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48 [Preview Abstract] |
Tuesday, March 14, 2006 12:51PM - 1:03PM |
H16.00007: Theoretical study of Hydrogen Storage in Nanotubes and Nanoscrolls. George Froudakis A combination of \textit{ab-initio} and Molecular Dynamics methods is used for investigating the nature of atomic and molecular hydrogen interaction with C, SiC and BN Nanotubes and Nanoscrolls. The curvature of the tube wall together with the direction of the hydrogen approach is considered and evaluated. In addition the improvement of the storage capacity is tested under various conditions of doping, pressure and temperature. [Preview Abstract] |
Tuesday, March 14, 2006 1:03PM - 1:15PM |
H16.00008: The effect of metal clustering on hydrogen storage Puru Jena, Qian Wang, Qiang Sun, Yoshiyuki Kawazoe Hydrogen has been recognized as an ideal energy carrier and has the potential to reduce our dependence on fossil fuels which are not only limited but also are harmful to the environment. The success of a new hydrogen economy, however, depends upon our ability to find materials that can store hydrogen reversibly with high gravimetric and volumetric density and operate under moderate temperatures and pressures. Although a great deal of effort has recently been devoted to searching of such materials, none are known to meet the above conditions. Nanostructures offer new possibilities for hydrogen storage due to the novel chemistry. It has been shown very recently that coating of carbon nanostructures with \textbf{\textit{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, 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, and we show that Ti atoms would prefer to cluster on the C$_{60}$ 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. [Preview Abstract] |
Tuesday, March 14, 2006 1:15PM - 1:27PM |
H16.00009: Storing hydrogen in graphene layers with tunable interlayer spacing Yang Lei, Wenguang Zhu, Yan Song, Enge Wang, Zhenyu Zhang, Zhengxiao Guo Carbon nanostructures are being studied for hydrogen storage. However the nature of H-C interactions in such structures is unclear. We use first-principles simulation to model H adsorption between graphene layers. The adsorption of H$_{2}$ between layers is evaluated, particularly with respect to inter-layer variation thus simulating the effect of stressing the graphite for H storage. We note that H$_{2}$ dissociates when the inter-graphene distance is reduced (the graphite is compressed). When the ratio of H:C=1:1, the graphene changes from a planar to a diamond-like structure. The H-C interaction changes from weak physisorption to strong chemisorption. When the pressure is reduced, H atoms can recombine to form H$_{2}$ by overcoming a small energy barrier. Based on this work, we propose a new scheme for H storage in C nanostructures: by way of altering the inter-graphene distance, the C structure can effectively ``inhale,'' store and release hydrogen in a controlled manner. [Preview Abstract] |
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