In situ X-ray study of ammonia borane at high pressures

Chen, Jiuhua; Couvy, H.; Liu, Haozhe; Drozd, Vadym; Daemen, Luke L.; Zhao, Yusheng; Kao, C.‐C.

doi:10.1016/j.ijhydene.2010.07.085

Cited by 35 publications

(67 citation statements)

References 36 publications

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“…22,23 Since ammonia borane is a strong van der Waals complex, 24,25 it is crucial to include van der Waals forces in our simulations. Thus, all calculations have been performed with the vdW-DF1 26-29 exchange-correlation functional (i.e.…”

Section: Computational Detailsmentioning

confidence: 99%

Lowering the hydrogen desorption temperature of NH₃BH₃ through B-group substitutions

Welchman

Thonhauser

2015

J. Mater. Chem. A

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We present ab initio results for substitutions in the promising hydrogen-storage material NH 3 BH 3 to lower its hydrogen desorption temperature. Substitutions have already been investigated with significant success recently, but in all cases a less electronegative element is substituted for the protic hydrogen in the NH 3 group of NH 3 BH 3 . We propose a different route, substituting the hydridic hydrogen in the BH 3 group with a more electronegative element. To keep the gravimetric density high, we focus on the second period elements C, N, O, and F, all with higher electronegativity compared to H. In addition, we investigate Cu and S as possible substitutions. Our main results include Bader charge analyses, hydrogen binding energies, and kinetic barriers for the hydrogen release reaction in the gas phase as well as in the solid. While the different substituents show varying effects on the kinetic barrier and thus desorption temperature-some overshoot our goal while others have little effect-we identify Cu as a very promising substituent, which lowers the reaction barrier by approximately 37% compared to NH 3 BH 3 and thus significantly influences the hydrogen desorption temperature.

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Section: Computational Detailsmentioning

confidence: 99%

Lowering the hydrogen desorption temperature of NH₃BH₃ through B-group substitutions

Welchman

Thonhauser

2015

J. Mater. Chem. A

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“…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.…”

mentioning

confidence: 99%

“…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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“…Although, Custelcean and Dreger reported that only one phase transition occurs at 0.8 GPa, with the delay of some mode splitting until 2. 1.3 GPa and second order phase transition at 5 GPa based on x-ray diffraction study [63].…”

Section: High Pressure Studies Of Hydrogen Storage Materialsmentioning

confidence: 99%

“…Chen et al [63] has determined the pressure-temperature phase boundary between the I4mm phase and Cmc2 1 phase as negative Clapeyron slope indicating the transformation is of endothermic, although it is not in agreement with the observation of Anderson et al [64]. Kumar et al has reported the I4mm to Cmc2 1 phase transition occurring at 1.22 GPa and Cmc2 1 to P1 (monoclinic) phase transition occurring at 8 GPa by combined X-ray, Neutron and theoretical investigation [65].…”

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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In situ X-ray study of ammonia borane at high pressures

Cited by 35 publications

References 36 publications

Lowering the hydrogen desorption temperature of NH₃BH₃ through B-group substitutions

Lowering the hydrogen desorption temperature of NH₃BH₃ through B-group substitutions

Positional disorder in ammonia borane at ambient conditions

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

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In situ X-ray study of ammonia borane at high pressures

Cited by 35 publications

References 36 publications

Lowering the hydrogen desorption temperature of NH3BH3 through B-group substitutions

Lowering the hydrogen desorption temperature of NH3BH3 through B-group substitutions

Positional disorder in ammonia borane at ambient conditions

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

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Lowering the hydrogen desorption temperature of NH₃BH₃ through B-group substitutions

Lowering the hydrogen desorption temperature of NH₃BH₃ through B-group substitutions