- HYDRIDOALUMINATES OF ALKALINE METALS.
-
Compounds with general formula MAlH//4, M//3AlH//6, M//2M prime AlH//6 (M, M prime EQUVLNT Li, Na, K) have been studied for several years in the authors' laboratory, especially from a fundamental point of view. The authors present an overall picture of our research work concerning preparation, thermodynamic and structural properties of these complex hydrides. Thermodynamic properties were investigated by calorimetric measurements. The authors also performed thermogravimetric analysis and differential scanning calorimetry studies with special attention to phase transformations. Except for Li//3AlH//6, the hexahydridoaluminates crystallize with a cryolite (Na//3AlF//6) or elpasolite (K//2NaAlF//6) structure, generally pseudocubic.
- Bastide,Bureau,Claudy,Letoffe,El Hajri
-
-
Read Online
- Ionic liquids as an efficient medium for the mechanochemical synthesis of α-AlH3 nano-composites
-
Aluminum hydride (AlH3) is one of the most promising hydrogen storage materials that has a high theoretical hydrogen storage capacity (10.08 wt%) and relatively low dehydriding temperature (100-200 °C). In this work, we present a cost-effective route to synthesize the α-AlH3 nano-composite by using cheap metal hydrides and aluminum chloride as starting reagents and to achieve liquid state reactive milling. The LiH/AlCl3 and MgH2/AlCl3 reaction systems were systemically explored. The phase identification of the obtained products was carried out by XRD and the morphology observed by TEM characterization. It was found that the α-AlH3 nano-composite can be successfully synthesized by reactive milling of commercial AlCl3 and LiH in a neutral ionic liquid ([2-Eim] OAc). Based on XRD analysis and TEM observation, an average grain size of 56 nm can be obtained by the proposed mechanochemical process. By setting the isothermal dehydrogenation temperature between 80 and 160 °C, the as-synthesized α-AlH3 nano-composite exhibits an advantage in hydrogen desorption capacity and has fast dehydriding kinetics. The hydrogen desorption content of 9.93 wt% was achieved at 160 °C, which indicates the potential utilization of the prepared nanocomposite in hydrogen storage applications.
- Duan,Hu,Ma
-
-
Read Online
- Tuning hydrogen storage properties and reactivity: Investigation of the LiBH4NaAlH4 system
-
Tuning the hydrogen storage properties of complex metal hydrides is of vast interest. Here, we investigate the hydrogen release and uptake pathways for a reactive hydride composite, LiBH4-NaAlH4 utilizing in situ synchrotron radiation powder X-ray diffraction experiments. Sodium alanate transforms to sodium borohydride via a metathesis reaction during ball milling or by heating at T～95 °C. NaBH4 decomposes at ～340 °C in dynamic vacuum, apparently directly to solid amorphous boron and hydrogen and sodium gas and the latter two elements are lost from the sample. Under other conditions, T=400 °C and p(H2)=～1 bar, NaBH4 only partly decomposes to B and NaH. On the other hand, formation of LiAl is facilitated by dynamic vacuum conditions, which gives access to the full hydrogen contents in the LiBH4-NaAlH4 system. Formation of AlB2 is observed (T～450 °C) and other phases, possibly AlBx or Al1-xLixB2, were observed for the more Li-rich samples. This may open new routes to the stabilization of boron in the solid state in the dehydrogenated state, which is a challenging and important issue for hydrogen storage systems based on borohydrides.
- Ravnsb?k, Dorthe B.,Jensen, Torben R.
-
p. 1144 - 1149
(2011/01/09)
-
- PHYSIOCHEMICAL PATHWAY TO REVERSIBLE HYDROGEN STORAGE
-
In one embodiment of the present disclosure, a process for cyclic dehydrogenation and rehydrogenation of hydrogen storage materials is provided. The process includes liberating hydrogen from a hydrogen storage material comprising hydrogen atoms chemically bonded to one or more elements to form a dehydrogenated material and contacting the dehydrogenated material with a solvent in the presence of hydrogen gas such that the solvent forms a reversible complex with rehydrogenated product of the dehydrogenated material wherein the dehydrogenated material is rehydrogenated to form a solid material containing hydrogen atoms chemically bonded to one or more elements.
- -
-
Page/Page column 17-19; 24
(2008/06/13)
-
- Physiochemical pathway for cyclic dehydrogenation and rehydrogenation of LiAlH4
-
A five-step physiochemical pathway for the cyclic dehydrogenation and rehydrogenation of LiAlH4 from Li3AlH6, LiH, and Al was developed. The LiAlH4 produced by this physiochemical route exhibited excellent dehydrogenation kinetics in the 80-100 °C range, providing about 4 wt % hydrogen. The decomposed LiAlH4 was also fully rehydrogenated through the physiochemical pathway using tetrahydrofuran (THF). The enthalpy change associated with the formation of a LiAlH4· 4THF adduct in THF played the essential role in fostering this rehydrogenation from the Li3AlH6, LiH, and Al dehydrogenation products. The kinetics of rehydrogenation was also significantly improved by adding Ti as a catalyst and by mechanochemical treatment, with the decomposition products readily converting into LiAlH4 at ambient temperature and pressures of 4.5-97.5 bar.
- Wang, Jun,Ebner, Armin D.,Ritter, James A.
-
p. 5949 - 5954
(2007/10/03)
-
- Synthesis of Sodium Tetrahydridoaluminate from Sodium and Aluminium Binary Hydrides in Diethyl Ether
-
Mechanochemically promoted reactions between sodium and aluminum binary hydrides in diethyl ether in the presence of various promoters are studied. It is observed that a complexing reaction resulting in NaAlH4 is substantially promoted when LiAlH4 is added to the solution in a molar ratio of LiAlH4 : AlH3 = (1 - 2) : 1. NaAlH4 addition to the suspension has a smaller effect. In the presence of LiBH4, a cation-exchange reaction occurs to form LiAlH4 and NaBH4.
- Bulychev, B. M.,Golubeva, A. V.,Storozhenko, P. A.
-
p. 971 - 974
(2008/10/08)
-
- Reactions of Secondary Amines with Lithium Tetrahydridoaluminate
-
Reactions of diethylamine, diisopropylamine and 2,2,6,6-tetramethylpiperidine with LiAlH4 in various ethers have been studied.Only two well-defined products result from Et2NH, namely LiAlH(NEt2)3 and LiAl(NEt2)4.If molar ratios of Et2NH:LiAlH4 smaller than 3:1 are employed all compounds of the series LiAlH(4-n)(NEt2)n (n = 0, 1, 2, 3) are present in solutions of tetrahydrofuran and diglyme.In diethylether insoluble materials consisting predominantly of lithium diethylaminohydridoaluminates and, presumably, small quantities of Li3AlH6 are also formed.At ambient temperature diisopropylamine reacts slowly with LiAlH4, and LiAlH2(NiPr2)2 can be isolated as a well-defined substitution product. 2,2,6,6-tetramethylpiperidine (tmpH) replaces only a single hydride from LiAlH4 with formation of LiAlH3(tmp).The reactions have been monitored by 7Li, 13C and 27Al NMR spectroscopy, and the structure of LiAlH(NEt2)3 has been determined by X-ray analysis.The monoclinic compound contains chains of AlHN3 and LiHN3 tetrahedra linked through common edges. - Keywords: Lithium-tris(diethylamino)hydridoaluminate, Lithium-bis(diisopropylamino)dihydridoaluminate, Lithium(tetramethylpiperidino)trihydridoaluminate, NMR Spectra, X-Ray
- Linti, Gerald,Noeth, Heinrich,Rahm, Peter
-
p. 1101 - 1112
(2007/10/02)
-
