First-principles study on lithium amide for hydrogen storage

Miwa, Kenji; Ohba, Nobuko; Towata, Shin‐ichi; Nakamori, Yoshiteru; Orimo, Shin Ichi

doi:10.1103/physrevb.71.195109

Cited by 137 publications

(154 citation statements)

References 34 publications

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“…Band-gap values ranging from ∼3 to 3.48 eV have been reported for LiNH 2 . [18][19][20] An analysis of the wavefunctions shows that the VBM is composed of Nrelated unbonded states from the (NH 2 ) − units, whereas the CBM is composed of a mixture of N p and H s states. Figure 3 shows the calculated band structure of orthorhombic Li 2 NH along the high-symmetry directions of the orthorhombic BZ.…”

Section: Bulk Propertiesmentioning

confidence: 99%

“…17 Theoretical studies of LiNH 2 and Li 2 NH to date have focused mainly on structural, electronic, and thermodynamic properties of the bulk compounds. [18][19][20][21][22][23][24] Experimental data, 16 on the other hand, suggest that the ratelimiting process in the Li amide/imide reaction involves mass transport mediated by point defects. This scenario motivated us to perform first-principles calculations for point defects and defect complexes in LiNH 2 and Li 2 NH in order to explore possible defect-related mechanisms that can explain the decomposition of LiNH 2 [reaction (3)] and the hydrogenation of Li 2 NH.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms for the decomposition and dehydrogenation of Li amide/imide

2012

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Reversible reaction involving Li amide (LiNH2) and Li imide (Li2NH) is a potential mechanism for hydrogen storage. Recent synchrotron x-ray diffraction experiments [W. I. David et al., J. Am. Chem. Soc. 129, 1594] suggest that the transformation between LiNH2 and Li2NH is a bulk reaction that occurs through non-stoichiometric processes and involves the migration of Li + and H + ions. In order to understand the atomistic mechanisms behind these processes, we carry out comprehensive first-principles studies of native point defects and defect complexes in the two compounds. We find that both LiNH2 and Li2NH are prone to Frenkel disorder on the Li sublattice. Lithium interstitials and vacancies have low formation energies and are highly mobile, and therefore play an important role in mass transport and ionic conduction. Hydrogen interstitials and vacancies, on the other hand, are responsible for forming and breaking N−H bonds, which is essential in the Li amide/imide reaction. Based on the structure, energetics, and migration of hydrogen-, lithium-, and nitrogen-related defects, we propose that LiNH2 decomposes into Li2NH and NH3 according to two competing mechanisms with different activation energies: one mechanism involves the formation of native defects in the interior of the material, the other at the surface. As a result, the prevailing mechanism and hence the effective activation energy for decomposition depend on the surface-tovolume ratio or the specific surface area, which changes with particle size during ball milling. These mechanisms also provide an explanation for the dehydrogenation of LiNH2+LiH mixtures.

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Section: Bulk Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

2012

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“…This is probably due to the fact that the electrostatic interaction between Li + and [B n H n ] 2− is not sensitive to n and a large part of this energy cancels out with that of LiH in Eq. (6 31 The nido and arachno borane are derived from closo borane by removing one and two vertices, respectively. These generate the salts in the ionized state as well as closo-type dianions.…”

Section: Stability Of Complex Anions : [Bnhn] 2−mentioning

confidence: 99%

First-principles study on the stability of intermediate compounds ofLiBH4

et al. 2006

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We report the results of the first-principles calculation on the intermediate compounds of LiBH4. The stability of LiB3H8 and Li2BnHn(n = 5−12) has been examined with the ultrasoft pseudopotential method based on the density functional theory. Theoretical prediction has suggested that monoclinic Li2B12H12 is the most stable among the candidate materials. We propose the following hydriding/dehydriding process of LiBH4 via this intermediate compound :LiH + 13 12 H2 ↔LiH + B + 3 2 H2. The hydrogen content and enthalpy of the first reaction are estimated to be 10 mass% and 56 kJ/mol H2, respectively, and those of the second reaction are 4 mass% and 125 kJ/mol H2. They are in good agreement with experimental results of the thermal desorption spectra of LiBH4. Our calculation has predicted that the bending modes for the Γ-phonon frequencies of monoclinic Li2B12H12 are lower than that of LiBH4, while stretching modes are higher. These results are very useful for the experimental search and identification of possible intermediate compounds.

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“…1 An interesting complex hydride for hydrogen storage is lithium amide (LiNH 2 ). [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Studies on such a hydride are motivated by the reversible absorption and desorption of hydrogen accomplished via the formation of lithium imide (Li 2 NH), as demonstrated by Chen et al 10 :…”

Section: Introductionmentioning

confidence: 99%

Native defects in LiNH2: A first-principles study

Wang

et al. 2011

Phys. Rev. B

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Native defects in lithium amide (LiNH 2 ), a promising candidate for hydrogen storage, are investigated by first-principles calculations based on density functional theory. We examine the structural properties and formation energies of H-, Li-, and N-related defects in all possible states. We find that the dominant H-and Li-related defects are in charged states, i.e., negatively charged H vacancy (V H − ), positively charged H interstitial (H i + ), negatively charged Li vacancy (V Li − ), and positively charged Li interstitial (I Li + ). V Li − and I Li + are present in the highest concentration. The positively charged NH 2 vacancy has the lowest formation energy among N-related defects. Furthermore, migration processes of the dominant defects are investigated. V Li − diffuses most rapidly with the lowest migration energy of 0.20 eV. Both formation and migration energies of Li-related dominant defects are found to be lower than those of H-related dominant defects. With an activation energy of 0.72 eV, V Li − is the major diffusive species in LiNH 2 . Our results further indicate that the formation of H i is the bottleneck for H transport.

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First-principles study on lithium amide for hydrogen storage

Cited by 137 publications

References 34 publications

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

First-principles study on the stability of intermediate compounds ofLiBH4

Native defects in LiNH2: A first-principles study

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