Pressure-induced complexation of NH3BH3–H2

Chellappa, Raja; Somayazulu, Maddury; Struzhkin, Viktor V.; Autrey, Tom; Hemley, Russell J.

doi:10.1063/1.3174262

Cited by 44 publications

(52 citation statements)

References 51 publications

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“…This latter study seemed to confirm that a higher concentration of H 2 than 1 : 1 is required for the strong weakening of H 2 vibron frequencies since a study of the SiH 4 ÁH 2 mixture showed a strengthening of vibron frequencies with increasing pressure. This contrasted with the vibron pressure dependence reported in inert-gas mixtures with hydrogen 25,26 or other gases mixed with hydrogen 27,28 where hydrogen vibron frequencies increase with pressure below 100 GPa and the mixtures remained insulating.…”

Section: Recent Approaches For Metallization Of Hydrogencontrasting

confidence: 84%

Metallization of solid hydrogen: the challenge and possible solutions

Klug

Yao

2011

Phys. Chem. Chem. Phys.

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The search for the means to convert molecular hydrogen to a metal under static conditions at high pressure is reviewed with emphasis on selected recent developments in both experimental studies and theoretical approaches. One approach suggested recently makes use of mixtures of hydrogen and suitable impurities. In these materials hydrogen is perturbed by impurities with the goal of obtaining the metallization of hydrogen at moderate pressures. This approach has also been extensively examined through the use of first-principles methods and we review this recently explored experimental approach and several theoretical studies that have provided an atomic-scale picture of the interaction of hydrogen with impurities under pressure. The objective of this novel approach is to help determine if metallization of hydrogen at pressures is attainable with currently available experimental techniques.

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Section: Recent Approaches For Metallization Of Hydrogencontrasting

confidence: 84%

Metallization of solid hydrogen: the challenge and possible solutions

Klug

Yao

2011

Phys. Chem. Chem. Phys.

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“…Raman spectra ( Fig. 1) of ammonia borane (25)(26)(27)(28)(29)(30) and lithium amidoborane (31) at ambient condition have been well documented, and the major Raman modes can be described by their molecular nature: N-H stretching, B-H stretching, and B-N stretching modes. In the Raman spectra, B-H stretching modes of lithium amidoborane appear at lower wavenumbers compared with those of ammonia borane ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…High-pressure study of molecular crystals can provide unique insight into the intermolecular bonding forces, such as hydrogen bonding and phase stability in hydrogen storage materials and thus provides insight into the improvement of design (22)(23)(24)(25)(26)(27)(28)(29)(30). For instance, Raman spectroscopic study of ammonia borane at high pressure provided insight about its phase transition behavior and the presence of dihydrogen bonding in its structure (25)(26)(27)(28)(29)(30).…”

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confidence: 99%

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High-pressure study of lithium amidoborane using Raman spectroscopy and insight into dihydrogen bonding absence

Najiba

Chen

2012

Proc. Natl. Acad. Sci. U.S.A.

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One of the major obstacles to the use of hydrogen as an energy carrier is the lack of proper hydrogen storage material. Lithium amidoborane has attracted significant attention as hydrogen storage material. It releases ∼10.9 wt% hydrogen, which is beyond the Department of Energy target, at remarkably low temperature (∼90°C) without borazine emission. It is essential to study the bonding behavior of this potential material to improve its dehydrogenation behavior further and also to make rehydrogenation possible. We have studied the high-pressure behavior of lithium amidoborane in a diamond anvil cell using in situ Raman spectroscopy. We have discovered that there is no dihydrogen bonding in this material, as the N-H stretching modes do not show redshift with pressure. The absence of the dihydrogen bonding in this material is an interesting phenomenon, as the dihydrogen bonding is the dominant bonding feature in its parent compound ammonia borane. This observation may provide guidance to the improvement of the hydrogen storage properties of this potential material and to design new material for hydrogen storage application. Also two phase transitions were found at high pressure at 3.9 and 12.7 GPa, which are characterized by sequential changes of Raman modes.H ydrogen economy has been considered as potentially efficient and environmental friendly alternative energy solution (1). However, one of the most important scientific and technical challenges facing the "hydrogen economy" is the development of safe and economically viable on-board hydrogen storage for fuel cell applications, especially to the transportation sector. Ammonia borane (BH 3 NH 3 ), a solid state hydrogen storage material, possesses exceptionally high hydrogen content (19.6 wt%) and in particular, it contains a unique combination of protonic and hydridic hydrogen, and on this basis, offers new opportunities for developing a practical source for generating molecular dihydrogen (2-5). Stepwise release of H 2 takes place through thermolysis of ammonia borane, yielding one-third of its total hydrogen content (6.5 wt%) in each heating step, along with emission of toxic borazine (6-8). Recently, research interests are focusing on how to improve discharge of H 2 from ammonia borane, including lowering the dehydrogenation temperature and enhancing hydrogen release rate using different techniques, e.g., nanoscaffolds (9), ionic liquids (10), acid catalysis (11), base metal catalyst (12), or transition metal catalysts (13, 14). More recently, significant attention is given to chemical modification of ammonia borane through substitution of one of the protonic hydrogen atoms with an alkali or alkaline-earth element (15-21). Lithium amidoborane (LiNH 2 BH 3 ) has been successfully synthesized by ball milling LiH with NH 3 BH 3 (15-18). One of the driving forces suggested for the formation of LiNH 2 BH 3 is the chemical potential of the protonic H δ+ in NH 3 and the hydridic H δ− in alkali metal hydrides making them tend to combine, producing H 2 + LiNH 2 BH 3 ....

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“…Wang et al (12) also recently presented experimental evidence that vibrational (vibron) frequencies are lowered at low pressures when hydrogen is added to SiH 4 . The behavior in SiH 4 ðH 2 Þ 2 contrasts with that of other mixtures of simple materials (13)(14)(15)(16) where hydrogen vibron frequencies increase with pressure in the pressure range below 100 GPa and they remain insulating. This observation indicates that the covalent bond in the H 2 molecules can be effectively modified at relatively low pressure with small change in chemical environment [there is only 11 atom percent Si in SiH 4 ðH 2 Þ 2 ], and would perhaps give rise to a unique metal with properties similar to metallic hydrogen.…”

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confidence: 83%

Silane plus molecular hydrogen as a possible pathway to metallic hydrogen

Yao

Klug

2010

Proc. Natl. Acad. Sci. U.S.A.

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The high-pressure behavior of silane, SiH 4 , plus molecular hydrogen was investigated using a structural search method and ab initio molecular dynamics to predict the structures and examine the physical origin of the pressure-induced drop in hydrogen intramolecular vibrational (vibron) frequencies. A structural distortion is predicted at 15 GPa from a slightly strained fcc cell to a rhombohedral cell that involves a small volume change. The predicted equation of state and the pressure-induced drop in the hydrogen vibron frequencies reproduces well the experimental data (Strobel TA, Somayazulu M, Hemley RJ (2009) Phys Rev Lett 103:065701). The bond weakening in H 2 is induced by intermolecular interactions between the H 2 and SiH 4 molecules. A significant feature of the high-pressure structures of SiH 4 ðH 2 Þ 2 is the dynamical behavior of the H 2 molecules. It is found that H 2 molecules are rotating in this pressure range whereas the SiH 4 molecules remain rigid. The detailed nature of the interactions of molecular hydrogen with SiH 4 in SiH 4 ðH 2 Þ 2 is therefore strongly influenced by the dynamical behavior of the H 2 molecules in the high-pressure structure. The phase with the calculated structure is predicted to become metallic near 120 GPa, which is significantly lower than the currently suggested pressure for metallization of bulk molecular hydrogen.first principles | hydrogen metallization | structure prediction O ne of the main challenges for condensed matter experimentalists and theoreticians for many decades has been to find the conditions where molecular hydrogen can be transformed to a metallic solid. The properties of metallic hydrogen could include high-temperature superconductivity (1), a liquid ground state (2), and conductivity at very high temperatures that gives rise to the strong magnetic fields of Jovian planets (3). The direct compression of solid molecular hydrogen however may require a pressure in excess of 400 GPa to reach a metallic state and this pressure lies at the upper limit of the current experimental static compression techniques (4, 5). There have been other approaches to this problem, including the study of hydrogen-rich molecular compounds (6). Compression of such compounds, in particular those involving group 14 elements, is predicted to lower the pressure required for metallization compared to pure bulk hydrogen (7,8). In these systems, the hydrogen can be viewed as perturbed by "impurities" in the material and "chemically precompressed" (6).An extension of this approach is to study mixtures of elements or simple molecules with hydrogen under pressure (9, 10). Recently, Strobel et al. (11) reported that by mixing silane (SiH 4 ) and hydrogen, a stoichiometric compound, SiH 4 ðH 2 Þ 2 , can be formed near 7 GPa. This compound has unique properties under pressure including a surprising weakening of the molecular hydrogen stretching frequencies. Wang et al. (12) also recently presented experimental evidence that vibrational (vibron) frequencies are lowered at low pressure...

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Pressure-induced complexation of NH3BH3–H2

Cited by 44 publications

References 51 publications

Metallization of solid hydrogen: the challenge and possible solutions

Metallization of solid hydrogen: the challenge and possible solutions

High-pressure study of lithium amidoborane using Raman spectroscopy and insight into dihydrogen bonding absence

Silane plus molecular hydrogen as a possible pathway to metallic hydrogen

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