Decomposition of Lithium Amide and Lithium Imide with and without

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Decomposition of Lithium Amide and Lithium Imide with and without Anion Promoter Junqing Zhang and Yun Hang Hu* Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, Michigan 49931-1295, United States ABSTRACT: The decompositions of lithium amide (LiNH2) and lithium imide (Li2NH) are important steps for hydrogen storage in Li3N. Herein, the decompositions of LiNH2 and Li2NH with and without anion promoter were investigated by using temperature-programmed decomposition (TPD) and X-ray diffraction (XRD) techniques. It was found that the decomposition of LiNH2 produced Li2NH and NH3 via two steps in the temperature range of 300450 °C: LiNH2 into a stable intermediate species (Li1.5NH1.5) and then into Li2NH. Furthermore, Li2NH is decomposed into Li, H2, and N2 without formation of Li3N in the temperature range of 550750 °C. The decompositions of LiNH2 and Li2NH can be promoted by chloride ion (Cl). The introduction of Cl into LiNH2 resulted in the generation of a new NH3 peak at low temperature of 250 °C besides the original NH3 peak at 330 °C in its TPD profiles. Furthermore, Cl can decrease the decomposition temperature of Li2NH by about 110 °C.

1. INTRODUCTION Hydrogen is considered one of the best alternative fuels.1,2 An effective hydrogen storage technology, which provides high storage capacity and fast kinetics, is a critical factor in the development of a hydrogen fuel for transportation. So far, three types of technologies are available to store hydrogen: liquefying hydrogen, compressing hydrogen, and hydrogen absorption/ adsorption in a solid material. The large amount of energy consumed during liquefaction and the continuous boil-off of hydrogen limit the possible use of liquid hydrogen storage technology.1 Compressing hydrogen requires a very high pressure to achieve enough hydrogen fuel for a reasonable driving cycle of 400 500 km, and this causes a safety issue related to tank rupture in an accident.2 For those reasons, hydrogen storage solid materials are now seen as the safest and most effective way of routinely handling hydrogen for transportation application.3 Therefore, the emphasis of hydrogen storage was and will be focused on solid storage materials. In general, the hydrogen storage in solid materials is achieved via two processes: chemical reactions, in which the hydrogen reacts with the solid material to form new compounds, and adsorption, in which the hydrogen is adsorbed on the solid material. Materials for hydrogen storage via the chemical reactions include metals,4 complex hydrides,5,6 and nitrides.719 The materials with relatively high hydrogen storage capacities usually require a hydrogen-releasing temperature higher than 100 °C (some of them even higher than 200 °C), because a relatively high energy is needed to break chemical bonds. On the other hand, the release temperature of hydrogen is usually low if the hydrogen is stored in a solid material via adsorption.2022 However, the hydrogen storage via the adsorption has a lower hydrogen capacity. Recently, hydrogen storage in clathrate hydrogen hydrates was explored.2327 The hydrogen storage in this type of materials is achieved by capturing the hydrogen in H2O-cages, instead of via chemical reaction or adsorption. Because the hydrogen hydrates are neither flammable nor corrosive, they provide a safe and environmentally friendly material to store r 2011 American Chemical Society

hydrogen. However, it still remains a challenge to employ hydrogen hydrates as practical hydrogen storage materials. For examples, formation of hydrogen hydrate is a slow process. The permanent cooling, which is necessary to keep hydrogen hydrates stable, may be another issue. Since 2002, Li3N has attracted much attention for hydrogen storage,719 which is based on the following hydrogenation and dehydrogenation: Li3 N þ H2 ¼ Li2 NH þ LiH

ΔH ¼ 148:07 kJ=mol H2 ð1Þ

Li2 NH þ H2 ¼ LiNH2 þ LiH


2LiNH2 ¼ Li2 NH þ NH3

ΔH ¼ 84:1 kJ=mol NH3 ð3Þ

LiH þ NH3 ¼ LiNH2 þ H2


Because further dehydrogenation of Li2NH/LiH back to Li3N (the reverse direction of reaction 1) is very difficult, the attention was focused on reaction 2 as a reversible hydrogen storage process, which provides 6.5 wt % hydrogen capacity. The dehydrogenation mechanism of LiNH2/LiH consists of two steps with NH3 intermediate species (eqs 3 and 4).7 The reaction between NH3 and LiH (eq 4) was exothermic and ultra fast.7 Therefore, the decomposition of LiNH2 (eq 3) is the ratedetermining step, which requires a high temperature. Current efforts to solve this issue are being focused on the introduction of Received: January 13, 2011 Accepted: May 19, 2011 Revised: May 17, 2011 Published: May 19, 2011 8058

dx.doi.org/10.1021/ie2008696 | Ind. Eng. Chem. Res. 2011, 50, 8058–8064

Industrial & Engineering Chemistry Research metal or cation promoters, including Mg, Ni, Fe, Co, Mn, V, and Ti.1719 As the realization of the important roles that anions play in biology,2830 catalysis,31 and the environment32,33 has grown, interest in anion chemistry has become more widespread. For example, the stringent environmental regulations on the sulfur content in transportation fuels force ones to use hydrotreatment catalysts with enhanced hydrogenating and acid functionalities to improve the removal of the most refractory sulfur compounds, substituted dibenzothiophenes, from the different petroleum fractions. Anion-modified alumina-based catalysts present these characteristics.34,35 This work stimulated much interest to reveal why the doping-anion can exhibit such a remarkable promoting effect. Nevertheless, effects of doping-anions on hydrogen storage materials have attracted limited attention. One of the reasons is probably that the anion of a promoter is always accompanied by a corresponding cation. The effect of the promoter is often attributed to its cation instead of its anion. However, recently, the anion promoting effects on hydrogen storage in LiBH4 and MgH2 were reported.3639 Furthermore, in the LiNH hydrogen storage system, LiNH2 doped with LiBH4 was intensively studied.4043 This proved the effect of the [BH4] anion on hydrogen storage in the LiNH system. In this work, the systematical evaluation for the decompositions of LiNH2 and Li2NH was carried out. Furthermore, the effect of Cl anion on their decomposition was also examined, because Cl anion was widely employed as a promoter to improve various catalysts. As a result, the decomposition mechanisms were established, and remarkable effects of Cl anion were found.

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Figure 1. (a) TPD-TCD profile and (b) TPD-MS profile of pure LiNH2.

then cooling to room temperature. The obtained samples were subjected to XRD measurements, which were performed with a Siemens D500 X-ray diffraction instrument equipped with a Cu KR source, at 45 kV and 35 mA. The scanning speed was 1°/min. The mixture of LiNH2 and LiCl samples was covered with plastic wrap during the XRD measurements to prevent LiCl from absorbing the H2O in air.

2. EXPERIMENTS 2.1. Sample Preparations. Lithium amide powder (95%) and

lithium chloride reagent (99þ %), which had been purchased from Aldrich Chemical Co., were used without any further purification. The introduction of lithium chloride into lithium amide was carried out by mixing them with an agate mortar and pestle for 5 min in an argon-filled glovebox to protect from oxidation. The molar ratio of lithium amide and lithium chloride in the mixtures varied from 9:1 to 1:9. 2.2. Temperature-Programmed Decomposition. The temperature-programmed decomposition (TPD) experiments were performed as follows: A sample (0.01 g) was loaded into a vertical quartz tube reactor, which was located in an electric tube furnace. The temperature of the reactor was increased to 800 °C at a rate of 5 °C/min. Argon (30 mL/min) was employed as a carrier gas through the reactor to bring the gaseous products of the decomposition of the sample into a thermal conductivity detector (TCD), generating a TPD-TCD profile. Furthermore, to determine all gas products except hydrogen, helium was used to carry the products from the TPD reactor into a mass spectrometer (HP Quadrupole, 5970 series mass selective detector) instead of TCD detector, generating a TPD-MS profile. The masses from 16.7 to 17.7 were used to monitor NH3 and from 27.7 to 28.7 to detect N2. 2.3. Powder X-ray Diffraction (XRD). A sample (0.1 g) was loaded into a vertical quartz tube reactor (5 mm diameter) located in an electric tube furnace. Argon (30 mL/min) was introduced into the reactor at room temperature, followed by heating to a selected temperature at a rate of 5 °C/min and

3. RESULTS AND DISCUSSION It is well-known that the decomposition of LiNH2 can produce Li2NH and NH3.44,45 However, the answers for the two questions are still unknown: whether hydrogen is formed during the decomposition of LiNH2 and how Li2NH further decomposes. To clarify them, LiNH2 was subjected to temperature-programmed decompositions (TPD) with TCD and MS detectors. As shown in Figure 1, one can see that the TPD-TCD and TPD-MS profiles are very similar. Furthermore, the TPDMS profile showed that NH3 was formed in the temperature range of 160470 °C and N2 produced between 520 and 800 °C. However, hydrogen cannot be detected by the MS detector due to the limitation of the MS instrument. In contrast, the TPDTCD provides total signals of all gases due to their different thermal conductivities from the carrier gas (argon). In other words, all three possible gas products (H2, NH3, and N2) can contribute to the peaks in the TPD-TCD profile. To clarify whether the peaks between 160 and 470 °C are associated with hydrogen, the gas products from the temperature-programmed decomposition of LiNH2 were cooled to 159 K before entering a TCD or MS detector. As a result, the peaks between 160 and 500 °C disappeared (Figure 2). The boiling temperatures of H2 (20.28 K) and N2 (77.36 K) are lower than the cooling temperature (159 K), whereas the melting temperature of NH3 (195 K) is higher than the cooling temperature. Therefore, the disappearance of the peak between 160 and 500 °C should be due to the condensation of NH3. A small bump between 200 and 500 °C can be observed in Figure 2a. The further analysis of a gas 8059

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Figure 4. XRD pattern of Li2NH prepared via heating LiNH2 at 400 °C for 12 h in a vacuum.

Figure 2. (a) TPD-TCD profile and (b) TPD-MS profile of LiNH2 with a cooler where produced gases were cooled to 159 K before entering TCD and MS detectors.

Figure 5. TPD-TCD profile of Li2NH.

Figure 6. (a) TPD-TCD profile and (b) TPD-MS profile of Li3N.

Figure 3. XRD patterns of the solid products from the TPD process of LiNH2 that was stopped at (a) room temperature, (b) 160 °C, (c) 330 °C, (d) 380 °C, (e) 520 °C, (f) 570 °C, (g) 645 °C, and (h) 690 °C.

chromatography (GC) equipped with TCD detector and a Porapak Q column revealed that the small bump is due to a small amount of H2 and N2. In other words, the peaks at 350 °C in Figure 1a consist of mainly NH3 with a very little amount of H2

and N2. Such a negligible amount of N2 and H2 may be due to the decomposition of NH3. Furthermore, the solid products from the TPD process were analyzed by XRD. As shown in Figure 3, one can see that the solid product obtained after the decomposition of LiNH2 at 330 °C or above was Li2NH. This indicates that the decomposition of LiNH2 produced NH3 and Li2NH between 160 and 500 °C, which can be expressed by eq 3. However, the decomposition process is not a single step, because there were two peaks (one at 330 °C and the other at 380 °C) between 160 and 470 °C in the TPD profiles (Figure 1). This means that the two steps were involved in the decomposition of LiNH2 into Li2NH and 8060



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Figure 7. (A) TPD-TCD profiles and (B) TPD-MS profiles of LiCl-doped LiNH2 with various LiNH2/LiCl mole ratios: (a) pure LiNH2, (b) 9:1, (c) 8:2, (d) 7:3, (e) 6:4, (f) 5:5, (g) 4:6, (h) 3:7, (i) 2:8, and (j) 1:9.

NH3. In other words, a stable intermediate species Li1þxNH2x (0 < x < 1), which is between LiNH2 and Li2NH, was formed as follows: ð1 þ xÞLiNH2 ¼ Li1þx NH2x þ xNH3

ð5Þ

2Li1þx NH2x ¼ ð1 þ xÞLi2 NH þ ð1 xÞNH3

ð6Þ

The value (0.5) of x was obtained from the TPD profiles (overlapped peaks in Figure.1a were resolved by Gaussian function fitting to obtain their areas), because the ratio of x to (1 x)/2 equals the ratio of the area of peak at 330 °C to the one at 380 °C. Therefore, the stable intermediate state is Li1.5NH1.5. During the hydrogenation of Li3N, Weidner et al. detected a series of nonstoichiometric lithium imides,46 in which compositions can be changed from Li1.70NH1.30 to Li1.02NH1.98.47,48 This would be dependent on the unique structure of Li2NH. Juza et al. first reported that the crystal structure of lithium imide (Li2NH) is an antifluorite face centered cubic (fcc) structure.44 Recently, Ohoyama et al.49 performed neutron powder diffraction experiments on Li2NH. They confirmed the fcc structure. However, they refined the positions of hydrogen atoms, because there is not any fully occupied model representing experimental data.

They found two partially occupied models that can explain the experimental data: Model I, in which every hydrogen is located at the 48h site of the Fm3m space group and the site occupancy of hydrogen is only 8.7%, and Model II, in which every hydrogen is located at the 16e site of the F43 m space group and the site occupancy of hydrogen is 27%. Furthermore, Noritake et al.50 carried out synchrotron X-ray powder diffraction experiments and charge density analysis for the same sample as Ohoyama et al. used. They also confirmed the antifluorite structure. On the basis of the Rietveld analysis accomplished for various structure models on the expected hydrogen sites around N atom, they revealed that both the structure model with hydrogen located at the 48h of the Fm3m space group and the model with hydrogen located at the 96j site of the Fm3m space group can well match their experimental data. Other models were also proposed.5154 Although those models have some differences, they reached the same conclusion that sites for N and Li are fully occupied but sites for H are only partially occupied. Each H atom randomly occupies the hydrogen sites around each N. In other words, the crystal structure of Li2NH is a hydrogen disordered structure, which has a huge number of unoccupied hydrogen sites. As a result, hydrogen can be introduced into the unoccupied hydrogen sites around N in stoichiometric lithium imide (Li2NH) to form a series of nonstoichiometric intermediate species between 8061



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shiny matter attached to the inner wall of the quartz tube reactor after LiNH2 decomposition at 800 °C, indicating the formation of Li. Therefore, the decomposition of Li2NH took place via the following reaction: 2Li2 NH ¼ 4Li þ H2 þ N2

Figure 8. XRD patterns of the solid products from the TPD process of LiNH2/LiCl (8:2 molar ratio) that was stopped at various temperatures: (a) room temperature, (b) 160 °C, (c) 275 °C, (d) 320 °C, (e) 330 °C, (f) 380 °C, (g) 520 °C, and (h) 570 °C.

LiNH2 and Li2NH. This can explain why the stable intermediate species (Li1.5NH1.5) was observed during the thermal decomposition of LiNH2. Furthermore, recently, Crivello et al. reported density functional theory calculations for intermediate LiNH compounds.55 Their results showed that the formation of the intermediate Li1.5NH1.5 is possible, and it should occupy a cubic Li-vacant-type structure, in which ordered [NH]2 and [NH2] anions coexist. Therefore, our detected stable intermediate Li1.5NH1.5 compound is consistent with the DFT prediction. From the above discussion, one can conclude that the peaks above 500 °C in the TPD profiles of LiNH2 were due to the decomposition of Li2NH. This can be further supported by the following experiments. A sample of Li2NH was prepared via the conventional approach, in which LiNH2 was heated at 400 °C in a vacuum for 12 h. The obtained sample was confirmed as Li2NH by XRD measurement (Figure 4). Indeed, the TPD profile of Li2NH contains peaks only above 500 °C (Figure 5). Furthermore, to clarify whether the peaks above 500 °C contain H2 besides N2, the gases generated from the TPD of Li2NH were analyzed by a gas chromatography (GC) equipped with TCD detector and a Porapak Q column for each 2 min. The results showed that the peaks above 500 °C consist of H2 and N2 with 1:1 molar ratio. Although Li is too reactive to be detected by XRD before it transferred into Li2O and LiOH during its relocation from the reactor to the XRD instrument, we did see

ΔH ¼ 444 kJ=mol H2

ð7Þ

In other words, Li2NH is decomposed into Li, H2, and N2 without Li3N formation. This can further be supported by the XRD measurement, in which no Li3N in the samples of LiNH2 decomposed at 645 and 690 °C was detected (Figure 3). Furthermore, Li3N sample was subjected to TPD measurements. As shown in Figure 6, one can see that Li3N started to decompose at 470 °C, which is lower than that (550 °C) of Li2NH. This indicates that Li2NH is more stable than Li3N, which can explain why no Li3N can be formed in the decomposition of Li2NH. With the temperature rising from 570 to 690 °C, there is an obvious peak-shifting in the XRD pattern of Li2NH (Figure 3), corresponding to the change of cubic lattice parameter from 5.083 to 4.950 Å. This indicates that high temperature led to the shrink of the imide crystal structure. This happened probably because lithium imide (Li2NH) lost some hydrogen at a high temperature, leading to the formation of nonstoichiometric imide as LixNH (2 < x). To examine the effect of anion (Cl) on the decomposition of LiNH2, Cl was doped into LiNH2 via mixing LiCl and LiNH2 with various mole ratios from 1:9 to 9:1 so that any new cation was not introduced. The Cl-doped LiNH2 samples were subjected to TPD measurements with TCD and MS detectors. As shown in Figure 7, LiCl changed the TPD profiles of LiNH2; a new NH3 peak occurred at a low temperature of about 250 °C besides the original NH3 peak at 330 °C. This indicates that Cl promoted the decomposition of LiNH2 into Li2NH and NH3. This can be explained as the interaction between Cl and LiNH2, which can weaken the bond between Liþ and [NH2]. The interaction is determined by the contact between the surfaces of LiCl and LiNH2 particles to form an interface, which leads to the decomposition of LiNH2 at a low temperature. Furthermore, LiCl can absorb NH3 to form a series of lithium chloride ammonia complexes Li(NH3)xCl (x = 4, 3, 2, 1).56 Therefore, the temperature, at which we can detect NH3, is dependent on the stability of the complexes, which can decompose to release NH3 at temperature above 200 °C.56 This can explain why the new NH3 was detected at a temperature of about 250 °C. The original NH3 at 330 °C still remained, because the LiNH2 inside the particles does not contact LiCl. It would be noted that the peaks at about 100 °C were confirmed as a result of the reaction between H2O adsorbed on LiCl and LiNH2. The adsorbed H2O originated from the air due to exposing the sample to it. Furthermore, Cl exhibited an even greater effect on the peaks at high temperatures; the two peaks at 645 and 690 °C in the TPD profile of LiNH2 without Cl merged into a broad one in that of Cl-doped LiNH2. In addition, the peak temperature decreased from 645 to 530 °C with increasing LiCl content. It is well-known that LiCl can form a eutectic liquid phase with another Li-based ionic compound below 500 °C.57 Therefore, it is reasonable for us to believe that LiCl and Li2NH can form a eutectic liquid phase at about 500 °C. As a result, LiCl and Li2NH have a good contact, and thus Cl can catalyze the decomposition of Li2NH via the formation of ClLiN bonds. This catalytic performance of Cl was further supported by the XRD measurements, which showed that LiCl was still present 8062


Industrial & Engineering Chemistry Research after the decomposition of Li2NH (Figure 8). It should be noted that there is little evidence of Li2NH on the XRD pattern above 400 °C (Figure 8), probably because Li2NH became amorphous due to the formation of its eutectic phase with LiCl.

4. CONCLUSION The decompositions of LiNH2 and Li2NH with and without anion promoter were evaluated. It was found that the decomposition of LiNH2 produced Li2NH and NH3 via two steps: LiNH2 into a stable intermediate species (Li1.5NH1.5) and then into Li2NH. Furthermore, Li2NH is decomposed into Li, H2, and N2 without formation of Li3N. Chloride ion (Cl) had great effects on the decompositions of LiNH2 and Li2NH. The introduction of Cl resulted in the generation of a new peak at low temperature of about 250 °C besides the original peak at 330 °C in the decomposition of LiNH2 into Li2NH and NH3. Furthermore, Cl showed an even greater effect on the decomposition of Li2NH; the two peaks in TPD profiles merged into one, and the peak temperature decrease from 645 to 530 °C with increasing molar ratio of LiCl to LiNH2. ’ AUTHOR INFORMATION Corresponding Author

*Tel.: (906) 487-2261. E-mail: [email protected].

’ ACKNOWLEDGMENT This work was supported by the U.S. National Science Foundation (NSF-CBET-0931587). ’ REFERENCES (1) Schlapbach, L.; Z€uttel, A. Hydrogen-storage materials for mobile applications. Nature 2001, 414, 353. (2) Fichtner, M. Nanotechnological aspects in materials for hydrogen storage. Adv. Eng. Mater. 2005, 7, 443. (3) Trudeau, M. L. Advanced materials for energy storage. MRS Bull. 1999, 24, 23. (4) Sandrock, G. Handbook of Fuel Cell; John Wiley & Sons Ltd.: New York, 2003. (5) Bogdanovic, B.; Schwickardi, M. Ti-doped alkali metal aluminum hydrides as potential novel reversible hydrogen storage materials. J. Alloys Compd. 1997, 253, 1. (6) Jensen, C. M.; Gross, K. J. Development of catalytically enhanced sodium aluminum hydride as a hydrogen-storage material. Appl. Phys. A: Mater. Sci. Process. 2001, 72, 213. (7) (a) Hu, Y. H.; Ruckenstein, E. Ultra-fast reaction between LiH and NH3 during H2 storage in Li3N. J. Phys. Chem. A 2003, 107, 9737. (b) Ichikawa, T.; Hanada, N.; Isobe, S.; Leng, H.; Fujii, H. Mechanism of novel reaction from LiNH2 and LiH to Li2NH and H2 as a promising hydrogen storage system. J. Phys. Chem. B 2004, 108, 7887–7892. (8) Chen, P.; Xiong, Z.; Luo, J.; Lin, J.; Tan, K. L. Interaction of hydrogen with metal nitrides and imides. Nature 2002, 420, 302. (9) Hu, Y. H.; Ruckenstein, E. Highly effective Li2O/Li3N with ultrafast kinetics for H2 storage. Ind. Eng. Chem. Res. 2004, 43, 2464. (10) Ichikawa, T.; Hanada, N.; Isobe, S.; Leng, H. Y.; Fujii, H. Hydrogen storage properties in Ti catalyzed LiNH system. J. Alloys Compd. 2005, 404, 435. (11) Nakamori, Y.; Yamagishi, T.; Yokoyama, M.; Orimo, S. Synthesis of LiNH2 film by vacuum evaporation. J. Alloys Compd. 2004, 377, L1. (12) Kojima, Y.; Kawai, Y. Hydrogen storage of metal nitride by a mechanochemical reaction. Chem. Commun. 2004, 2210.

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(13) Markmaitree, T.; Ren, R. M.; Shaw, L. L. Enhancement of lithium amide to lithium imide transition via mechanical activation. J. Phys. Chem. B 2006, 110, 20710. (14) Yang, J.; Sudik, A.; Wolverton, C. Activation of hydrogen storage materials in the Li-Mg-N-H system: Effect on storage properties. J. Alloys Compd. 2007, 430, 334. (15) Dolotko, O.; Zhang, H. Q.; Ugurlu, O.; Wiench, J. W.; Pruski, M.; Chumbley, L. S.; Pecharsky, V. Mechanochemical transformations in Li(Na)AlH4-Li(Na)NH2 systems. Acta Mater. 2007, 55, 3121. (16) Luo, W. LiNH2-MgH2: a viable hydrogen storage system. J. Alloys Compd. 2004, 381, 284. (17) Nakamori, Y.; Orimo, S. LiN based hydrogen storage materials. Mater. Sci. Eng., B 2004, 108, 48. (18) Ichikawa, T.; Isobe, S.; Hanada, N.; Fujii, H. Lithium nitride for reversible hydrogen storage. J. Alloys Compd. 2004, 365, 271. (19) Yao, J. H.; Shang, C.; Aguey-Zinsou, K. F.; Guo, Z. X. Desorption characteristics of mechanically and chemically modified LiNH2 and (LiNH2 þ LiH). J. Alloys Compd. 2007, 432, 277. (20) Seayad, A. M.; Antonelli, D. M. Recent advances in hydrogen storage in metal-containing inorganic nanostructures and related materials. Adv. Mater. 2004, 16, 765. (21) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O’Keefe, M.; Yaghi, O. M. Hydrogen storage in microporous metal organic frameworks. Science 2003, 300, 1127. (22) Hu, Y. H.; Zhang, L. Hydrogen storage in metalorganic frameworks. Adv. Mater. 2010, 22, E117. (23) Mao, W. L.; Mao, H. K.; Goncharov, A. F.; Struzhkin, V. V.; Guo, Q.; Hu, J.; Shu, J.; Hemley, R. J.; Somayazulu, M.; Zhao, Y. Hydrogen clusters in clathrate hydrate. Science 2002, 297, 2247. (24) Mao, W. L.; Mao, H. K. Hydrogen storage in molecular compounds. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 708. (25) Florusse, L. J.; Peters, C. J.; Schoonman, J.; Hester, K. C.; Koh, C. A.; Dec, S. F.; Marsh, K. N.; Sloan, E. D. Stable low-pressure hydrogen clusters stored in a binary clathrate hydrate. Science 2004, 306, 469. (26) Lee, H.; Lee, J. W.; Kim, D. Y.; Park, J.; Seo, Y. T.; Zeng, H.; Moudrakovski, I. L.; Ratcliffe, C. I.; Ripmeester, J. A. Tuning clathrate hydrates for hydrogen storage. Nature 2005, 434, 743. (27) Patchkovskii, S.; Tse, J. S. Thermodynamic stability of hydrogen clathrates. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 14645. (28) Chakrabarti, P. J.; Smith, B. D. Anion binding sites in protein structures. Mol. Biol. 1993, 234, 463. (29) Mangani, S.; Ferraroni, M. Supramolecular Chemistry of Anions; Wiley-VCH: New York, 1997. (30) Sessler, J. L.; Sansom, P. I.; Andrievsky, A.; Kral, V. Supramolecular Chemistry of Anions; Wiley-VCH: New York, 1997. (31) Scheele, J.; Timmerman, P.; Reinhoudt, D. N. A significant effect of anion binding ureas on the product ratio in the palladium(II)catalyzed hydrocarbonylation of alkenes. Chem. Commun. 1998, 2613. (32) Glidewell, C. Nitrate/nitrite controversy. Chem. Br. 1990, 26, 137. (33) Holloway, J. M.; Dahlgren, R. A.; Hansen, B.; Casey, W. H. Contribution of bedrock nitrogen to high nitrate concentrations in stream water. Nature 1998, 395, 785. (34) Sun, M.; Prins, R. A kinetic investigation of the effects of fluorine and nickel on the HDN of toluidine on fully sulfided tungsten sulfide catalysts. J. Catal. 2001, 203, 192. (35) Schwartz, V.; Sun, M. Y.; Prins, R. An EXAFS study of the influence of fluorine on the structure of sulfided W/Al2O3 and NiW/ Al2O3 catalysts. J. Phys. Chem. B 2002, 106, 2597. (36) Wang, P.; Kang, X. D.; Cheng, H. M. Improved hydrogen storage of TiF3-doped NaAlH4. ChemPhysChem 2005, 6, 2488. (37) Yin, L. C.; Wang, P.; Kang, X. D.; Sun, C. H.; Cheng, H. M. Functional anion concept: effect of fluorine anion on hydrogen storage of sodium Alanate. Phys. Chem. Chem. Phys. 2007, 9, 1499. (38) Yin, L.; Wang, P.; Fang, Z.; Cheng, H. Thermodynamically tuning LiBH4 by fluorine anion doping for hydrogen storage: A density functional study. Chem. Phys. Lett. 2008, 450, 318. (39) Ma, L. P.; Kang, X. D.; Dai, H. B.; Liang, Y.; Fang, Z. Z.; Wang, P. J.; Wang, P.; Cheng, H. M. Superior catalytic effect of TiF3 over TiCl3 8063



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in improving the hydrogen sorption kinetics of MgH2: catalytic role of fluorine anion. Acta Mater. 2009, 57, 2250. (40) Pinkerton, F. E.; Meisner, G. P.; Meyer, M. S.; Balogh, M. P.; Kundrat, M. D. Hydrogen desorption exceeding ten weight percent from the new quaternary hydride Li3BN2H8. J. Phys. Chem. B 2005, 109, 6. (41) Aoki, M.; Miwa, K.; Noritake, T.; Kitahara, G.; Nakamori, Y.; Orimo, S.; Towata, S. Destabilization of LiBH4 by mixing with LiNH2. Appl. Phys. A: Mater. Sci. Process. 2005, 80, 1409. (42) Chater, P. A.; David, W. I. F.; Johnson, S. R.; Edwards, P. P.; Anderson, P. A. Synthesis and crystal structure of Li4BH4(NH2)3. Chem. Commun. 2006, 2439. (43) Chater, P. A.; Anderson, P. A.; Prendergast, J. W.; Walton, A.; Mann, V. S. J.; Book, D.; David, W. I. F.; Johnson, S. R.; Edwards, P. P. Synthesis and characterization of amide-borohydrides: New complex light hydrides for potential hydrogen storage. J. Alloys Compd. 2007, 446447, 350. (44) Juza, R.; Opp, K. Z. Metallamide und metallnitride, 25. Mitteilung. Zur kenntnis des lithiumimides. Anorg. Allg. Chem. 1951, 266, 325. (45) Pinkerton, F. E. Decomposition kinetics of lithium amide for hydrogen storage materials. J. Alloys Compd. 2005, 400, 76. (46) Alapati, S. V.; Johnson, J. K.; Sholl, D. S. Identification of destabilized metal hydrides for hydrogen storage using first principles calculations. J. Phys. Chem. B 2006, 110, 8769. (47) David, W. I. F.; Jones, M. O.; Gregory, D. H.; Jewell, C. M.; Johnson, S. R.; Walton, A.; Edwards, P. P. A mechanism for nonstoichiometry in the lithium amide/lithium imide hydrogen storage reaction. J. Am. Chem. Soc. 2007, 129, 1594. (48) Weidner, E.; Bull, D. J.; Shabalin, I. L.; Keens, S. G.; Telling, M. T. F.; Ross, D. K. Observation of novel phases during deuteration of lithium nitride from in situ neutron diffraction. Chem. Phys. Lett. 2007, 444, 76. (49) Ohoyama, K.; Nakamori, Y.; Orimo, S.; Yamada, K. Revised crystal structure model of Li2NH by neutron powder diffraction. J. Phys. Soc. Jpn. 2005, 74, 483. (50) Noritake, T.; Nozaki, H.; Aoki, M.; Towata, S.; Kitahara, G.; Nakamori, Y.; Orimo, S. Crystal structure and charge density analysis of Li2NH by synchrotron X-ray diffraction. J. Alloys Compd. 2005, 393, 264. (51) Balogh, M. P.; Jones, C. Y.; Herbst, J. F.; Hector, L. G., Jr.; Kundrat, M. Crystal structures and phase transformation of deuterated lithium imide, Li2ND. J. Alloys Compd. 2006, 420, 326. (52) Zhang, C. J.; Dyer, M.; Alavi, A. Quantum delocalization of hydrogen in the Li2NH crystal. J. Phys. Chem. B 2005, 109, 22089. (53) Mueller, T.; Ceder, G. Effective interactions between the N-H bond orientations in lithium imide and a proposed ground-state structure. Phys. Rev. B 2006, 74, 134104. (54) Magyari-K€ope, B.; Ozolin-s, V.; Wolverton, C. Theoretical prediction of low-energy crystal structures and hydrogen storage energetics in Li2NH. Phys. Rev. B 2006, 73, 220101. erny , R.; Latroche, M.; Chandra, D. (55) Crivello, J. C.; Gupta, M.; C Density functional study of Li4NH and Li1.5NH1.5 as intermediary compounds during hydrogenation of Li3N. Phys. Rev. B 2010, 81, 104113. (56) Bevers, E. R. T.; van Ekeren, P. J.; Haije, W. G.; Oonk, H. A. J. Thermodynamic properties of lithium chloride ammonia complexes for application in a high-lift high temperature chemical heat pump. J. Therm. Anal. Calorim. 2006, 86, 825. (57) Johnson, C. E.; Wood, S. E.; Crouthamel, C. E. Studies of lithium hydride systems. I. Solidliquid equilibrium in the lithium chloridelithium hydride system. Inorg. Chem. 1964, 3, 1487.

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Decomposition of Lithium Amide and Lithium Imide with and without

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