Raman spectroscopy study of ammonia borane at high pressure

Lin, Yu; Mao, Wendy L.; Drozd, Vadym; Chen, Jiuhua; Daemen, Luke L.

doi:10.1063/1.3040276

Cited by 73 publications

(121 citation statements)

References 43 publications

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“…Moreover, the splitting of these modes showed large hysteresis relative to the appearance of the H 2 vibrons. Evolution of the N-H and B-H stretching modes in pure AB has been well documented in this pressure range (19). At 8.2 GPa, the N-H spectrum consists of 2 peaks at 3,235 cm Ϫ1 and 3,291 cm Ϫ1 , and the B-H spectrum consists of a sharp peak at 2,372 cm Ϫ1 and an unresolved multiplet at 2,430-2,520 cm Ϫ1 .…”

Section: Resultsmentioning

confidence: 97%

“…The AB complex was synthesized at Los Alamos Neutron Science Center, Los Alamos National Laboratory. Details of its synthesis can be found elsewhere (19). Polycrystalline samples, together with small ruby chips for pressure calibration were loaded into a 0.2-mm-diameter sample chamber drilled in Be-Cu or Re gaskets.…”

Section: Methodsmentioning

confidence: 99%

“…A recent Raman spectroscopy study of AB reported 3 high-pressure phase transitions up to 22 GPa (19). Here, we investigated the highpressure behavior of AB in the presence of excess H 2 , and successfully synthesized a high-pressure compound of AB-H 2 .…”

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Storage of molecular hydrogen in an ammonia borane compound at high pressure

Lin

Mao

2009

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

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We studied ammonia borane (AB), NH3BH3, in the presence of excess hydrogen (H2) pressure and discovered a solid phase, AB(H2)x, where x Ϸ1.3-2. The new AB-H2 compound can store an estimated 8 -12 wt % molecular H2 in addition to the chemically bonded H2 in AB. This phase formed slowly at 6.2 GPa, but the reaction rate could be enhanced by crushing the AB sample to increase its contact area with H2. The compound has 2 Raman H2 vibron peaks from the absorbed H2 in this phase: one (1) at frequency 70 cm ؊1 below the free H2 vibron, and the other (2) at higher frequency overlapping with the free H2 vibron at 6 GPa. The peaks shift linearly over the pressure interval of 6 -16 GPa with average pressure coefficients of d1/dP ‫؍‬ 4 cm ؊1 /GPa and d2/dP ‫؍‬ 6 cm ؊1 /GPa. The formation of the compound is accompanied by changes in the N-H and B-H stretching Raman peaks resulting from the AB interactions with H2 which indicate the structural complexity and low symmetry of this phase. Storage of significant amounts of additional molecular H2 in AB increases the already high hydrogen content of AB, and may provide guidance for developing improved hydrogen storage materials. hydrogen storage materials ͉ energy H ydrogen has been touted for its potential to be an environmentally clean and efficient alternative energy carrier (1, 2). A major challenge to the use of hydrogen as an on-board energy source is the storage efficiency. Ammonia borane (AB), NH 3 BH 3 , a solid-state hydrogen storage material, has attracted attention due to its remarkably high hydrogen content (19.6 wt %) which exceeds 2015 Department of Energy target (9 wt %) for on-board hydrogen storage systems (3, 4). At ambient conditions AB crystallizes in a tetragonal space group I4 mm with a unit cell containing 2 molecules (5, 6). Dihydrogen bonding of the protonic (NH) and hydridic (BH) hydrogen atoms in adjacent molecules is attributed to the locking of structure in its 3-dimensional configuration (7). By stepwise release of H 2 through thermolysis, it can yield 6.5 wt %, one-third of its total H 2 , during each heating step. Extensive research has been conducted on how to effectively discharge H 2 from AB, including lowering the decomposition temperatures and increasing the rate of H 2 release through the use of acid (8, 9) or transition metal (10, 11) catalysts, ionic liquids (12), nanoscaffolds (13), etc.High-pressure studies can improve our understanding of the structural relationships in hydrogen storage materials and provide insight into improving the design (14, 15). High pressure can also stabilize new phases of H 2 plus other single second-row hydrates, like H 2 O (16, 17) and CH 4 (18). A recent Raman spectroscopy study of AB reported 3 high-pressure phase transitions up to 22 GPa (19). Here, we investigated the highpressure behavior of AB in the presence of excess H 2 , and successfully synthesized a high-pressure compound of AB-H 2 . An additional 8-12 wt % H 2 can be incorporated into the phase which can be formed at the pressure as low as 6.2 GPa...

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Section: Resultsmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 99%

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Storage of molecular hydrogen in an ammonia borane compound at high pressure

Lin

Mao

2009

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

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“…Since ammonia borane is a strong van der Waals complex [16,17], the inclusion of van der Waals forces is essential [10,18,19]; we thus use vdW-DF1 [20][21][22] (i.e., revPBE exchange and local-density approximation correlation in addition to the nonlocal contribution) as the exchange-correlation functional for all calculations. Car-Parrinello molecular dynamics (CPMD) was performed with the CP code (part of QUANTUM-ESPRESSO version 5.0.2; the vdW-DF capability in CP is a new feature, which we have just implemented) [23], using ultrasoft pseudopotentials and wave function and density cutoffs of 475 and 5700 eV.…”

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confidence: 99%

Positional disorder in ammonia borane at ambient conditions

2014

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We solve a long-standing experimental discrepancy of NH 3 BH 3 , which-as a molecule-has a threefold rotational axis, but in its crystallized form at room temperature shows a fourfold symmetry around the same axis, creating a geometric incompatibility. To explain this peculiar experimental result, we study the dynamics of this system with ab initio Car-Parrinello molecular dynamics and nudged-elastic band simulations. We find that rotations, rather than spatial static disorder, at angular velocities of 2 rev/ps-a time scale too small to be resolved by standard experimental techniques-are responsible for the fourfold symmetry. Ammonia borane NH 3 BH 3 has drawn significant interest in recent years because of its potential as a hydrogen storage material, with a gravimetric storage density of 19.6 mass% [1][2][3][4][5][6][7]. The structure of its solid phase has been explored previously [8][9][10][11][12][13], but the literature does not agree about the hydrogen behavior at room temperature. The molecule consists of a dative B-N bond and a trio of H atoms (henceforth referred to as a "halo") bonded to each of those two atoms, forming an hourglass shape, visible in Fig. 1. At low temperatures (0 ∼ 225 K), the solid exhibits an orthorhombic structure with space group Pmn2 1 . Heated above 225 K, it undergoes a phase transition to a body-centered tetragonal structure with space group I4mm. It is this room-temperature phase that exhibits unexpected experimental results: While the molecule itself has a threefold symmetry about the B-N axis, neutron [11,14] and x-ray [12,15,16] diffraction on the solid reveal a fourfold symmetry about the same axis, creating a geometric incompatibility within the structure. Investigating the dynamics of the system with ab initio methods, we find that the individual halos are rotating with angular velocity on the order of 0.7 • /fs ≈ 2 rev/ps, such that standard experiments can only probe the time-averaged positions, leading to the tetragonal host structure with fourfold symmetry.The precise behavior of these hydrogen halos has been the subject of several studies over three decades. In 1983, Reynhardt and Hoon [8] found threefold reorientations of the BH 3 and NH 3 groups with a tunneling frequency of 1.4 MHz in the orthorhombic phase. Penner et al. [9] found in 1999 that these groups reoriented independently. Deciphering the behavior in the tetragonal structure has been less straightforward. In the same 1983 study, Reynhardt and Hoon concluded that the BH 3 , and possibly the NH 3 groups, rotate freely. Brown et al. [11] found that they could describe the disorder entirely with threefold jump diffusion. Bowden et al. tried using a larger unit cell to model the same disorder as spatial variation rather than higher-order rotation; however, they found no evidence to support this model [12], leaving this disagreement unresolved in the literature. The present study aims to elucidate how the hydrogen halos behave in the solid, especially in the high-temperature, tetragonal structure. To this...

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“…In recent years, it has attracted much attention from high pressure scientists. Under ambient conditions, NH 3 BH 3 crystallizes into a tetragonal structure with the space group I4mm [54][55][56][57][58][59][60] and shows several kind of phase transitions which are induced by pressure. I4mm to Cmc2 1 (orthorhombic) phase transition at room temperature and high pressure is reported contradictorily.…”

Section: High Pressure Studies Of Hydrogen Storage Materialsmentioning

confidence: 99%

High Pressure and Low Temperature Study of Ammonia Borane and Lithium Amidoborane

Najiba¹

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During this dissertation, Raman spectroscopic study of lithium amidoborane has been carried out at high pressure in a diamond anvil cell. It has been identified that there is no dihydrogen bond in the lithium amidoborane structure, whereas dihydrogen bond is the characteristic bond of the parent compound ammonia borane. At high pressure up to 15 viii GPa, Raman spectroscopic study indicates two phase transformations of lithium amidoborane, whereas synchrotron X-ray diffraction data indicates only one phase transformation.Pressure and temperature has a significant effect on the structural stability of ammonia borane. This dissertation explored the phase transformation behavior of ammonia borane at high pressure and low temperature using in situ Raman spectroscopy.The P-T phase boundary between the tetragonal (I4mm) and orthorhombic (Pmn2 1

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Raman spectroscopy study of ammonia borane at high pressure

Cited by 73 publications

References 43 publications

Storage of molecular hydrogen in an ammonia borane compound at high pressure

Storage of molecular hydrogen in an ammonia borane compound at high pressure

Positional disorder in ammonia borane at ambient conditions

High Pressure and Low Temperature Study of Ammonia Borane and Lithium Amidoborane

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