Kinetics and hydrogen storage performance of Li-Mg-N-H systems doped with Al and AlCl3 (original) (raw)
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Effects of Al-based additives on the hydrogen storage performance of the Mg(NH2)2–2LiH system
Dalton Transactions, 2013
The Mg(NH 2 ) 2 -2LiH composite is a promising hydrogen storage material due to its relatively high reversible hydrogen capacity (∼5.6 wt%) and suitable thermodynamic properties that allow hydrogen sorption conducting at temperatures below 90°C. However, the presence of a severe kinetic barrier inhibits its low-temperature operation. In the present work, Li 3 AlH 6 was introduced to the Mg(NH 2 ) 2 -2LiH system.
Recent Advances on Mg–Li–Al Systems for Solid-State Hydrogen Storage: A Review
Frontiers in Energy Research
The problem of providing compact and safe storage solutions for hydrogen in solid-state materials is demanding and challenging. The storage solutions for hydrogen required high-capacity storage technologies, which preferably operate at low pressures and have good performances in the kinetics of absorption/desorption. Metal hydrides such as magnesium hydride (MgH2) are promising candidates for such storage solutions, but several drawbacks including high onset desorption temperature (>400°C) and slow sorption kinetics need to be overcome. In this study, we reviewed the recent developments in the hydrogen storage performance development of MgH2 and found that the destabilization concept has been extensively explored. Lithium alanate or LiAlH4 has been used as a destabilizing agent in MgH2–LiAlH4 (Mg–Li–Al) due to its high capacity of hydrogen, which is 10.5 wt.%, and low onset desorption temperature (∼150°C). In this article, a review of the recent advances in the Mg–Li–Al system fo...
Li–Mg–N–H-based combination systems for hydrogen storage
Journal of Alloys and Compounds, 2011
Metal-N-H-based materials are of particular interest as a group of new complex hydrides owing to their potential applications in hydrogen storage. A variety of metal-N-H-based systems have been developed so far for their hydrogen storage performances. This review deals with the Li-Mg-N-H-based combination systems which are widely recognized as one of the most promising hydrogen storage media for practical applications. The emphasis is on the structural characteristics of the lithium/magnesium amides/imides/nitrides, the hydrogen storage properties determined by the material compositions, the thermodynamics and kinetics of the hydrogen storage process, and the reaction mechanisms for de-/hydrogenation of the Li-Mg-N-H combination systems. The challenges and direction in further improving the hydrogen storage performances of the Li-Mg-N-H-based combination systems are pointed out as well.
Physical Review B, 2009
First-principles density-functional theory ͑DFT͒ calculations have been used to investigate the crystal structures, thermodynamic stability, and decomposition pathways of Li-Mg-Al-H hydrogen storage compounds. We find that the recently discovered LiMg͑AlH 4 ͒ 3 compound is stable with respect to solid-state decomposition into LiAlH 4 and Mg͑AlH 4 ͒ 2 ; however, we also find that LiMg͑AlH 4 ͒ 3 is unstable with respect to hydrogen release and decomposes exothermically into LiMgAlH 6 , Al, and H 2 with a calculated T = 300 K enthalpy of −7.3 kJ/ ͑mol H 2 ͒, in excellent agreement with the weakly exothermic value of −5 kJ/ ͑mol H 2 ͒ obtained from differential scanning calorimetry measurements ͓M. Mamatha et al., J. Alloys Compd. 407, 78 ͑2006͔͒. LiMgAlH 6 is a stable intermediate, which has two competing endothermic decomposition pathways for H 2 release: one going directly into the binary hydrides of Li and Mg and the other proceeding via the formation of an intermediate Li 3 AlH 6 phase, with room-temperature enthalpies of +18.6 and +16.6 kJ/ ͑mol H 2 ͒, respectively. Using database searching based on known crystal structures from the inorganic crystal structure database, we predict that the hypothetical MgAlH 5 compound should assume the orthorhombic BaGaF 5 prototype structure, in contrast to a previous DFT study of MgAlH 5 , ͓A. Klaveness et al., Phys. Rev. B 73, 094122 ͑2006͔͒. However, the decomposition enthalpy of MgAlH 5 is only weakly endothermic, +1.1 kJ/ ͑mol H 2 ͒, and therefore this compound is not expected to occur in the high-temperature decomposition sequence of Mg alanate. We also present a comprehensive investigation of the phonon spectra and vibrational thermodynamics of Li-Mg-Al-H compounds, finding that vibrations typically decrease reaction enthalpies by up to 10 kJ/ mol H 2 at ambient temperatures and significantly lower reaction entropies.
Journal of Power Sources, 2008
Reversible dehydrogenation and hydrogenation reactions have been reported for a number of reactions based on lithium alanate and lithium amide materials. The dehydrogenation and hydrogenation reactions involving these materials are, however, usually very complex. Significant discrepancies exist among different studies published in literature. Understanding the reaction mechanism and the dependence of the reaction pathway on material preparation processes and processing parameters is critical. In this paper, the hydrogenation reactions of the mixture of 3Li 2 NH/Al/4 wt%TiCl 3 were investigated as a function of the heating rate. The hydrogenated products were characterized by means of TGA, XRD and solid-state NMR. These new results showed that the reformation of Li 3 AlH 6 depends strongly on the heating rate during the hydrogenation process. The dehydrogenation and rehydrogenation reaction pathways and possible mechanisms of the combined system are, however, still under investigation.
Improved Dehydrogenation Properties of 2LiNH2-MgH2 by Doping with Li3AlH6
Metals, 2017
Doping with additives in a Li-Mg-N-H system has been regarded as one of the most effective methods of improving hydrogen storage properties. In this paper, we prepared Li 3 AlH 6 and evaluated its effect on the dehydrogenation properties of 2LiNH 2-MgH 2. Our studies show that doping with Li 3 AlH 6 could effectively lower the dehydrogenation temperatures and increase the hydrogen content of 2LiNH 2-MgH 2. For example, 2LiNH 2-MgH 2-0.1Li 3 AlH 6 can desorb 6.43 wt % of hydrogen upon heating to 300 • C, with the onset dehydrogenation temperature at 78 • C. Isothermal dehydrogenation testing indicated that 2LiNH 2-MgH 2-0.1Li 3 AlH 6 had superior dehydrogenation kinetics at low temperature. Moreover, the release of byproduct NH 3 was successfully suppressed. Measurement of the thermal diffusivity suggests that the enhanced dehydrogenation properties may be ascribed to the fact that doping with Li 3 AlH 6 could improve the heat transfer for solid-solid reaction.
Engineering review, 2011
It is observed that large quantities of hydrogen (H2) are released at ambient temperatures during the mechano-chemical synthesis of the Li-Al-N-Mg-based hydride composites using an energetic ball milling in a unique magneto-mill. For the (nLiAlH4+LiNH2; n=1, 3, 11.5, 30) composite, at the molar ratio n=1, the LiNH2 constituent destabilizes LiAlH4 and enhances its decomposition to Li3AlH6, Al and H2, and subsequently Li3AlH6 to LiH, Al and H2. LiNH2 ceases to destabilize LiAlH4 in the composites with increasing molar content of LiAlH4 (n≥3). For the (nLiAlH4+MnCl2; n=1, 3, 8, 13, 30, 63) composite, XRD phase analysis shows that chemical reaction occurs during ball milling between the hydride and chloride constituent forming either an inverse cubic spinel Li2MnCl4 for n=1 or lithium salt (LiCl) for n>1. Both reactions release hydrogen. For the (LiNH2+nMgH2; n=1, 1.5) composite the pathway of hydride reactions depends on the milling energy and milling time. Under low milling energy ...
Reaction steps in the Li–Mg–N–H hydrogen storage system
Journal of Alloys and Compounds, 2007
The reaction steps in mixtures of 2LiNH 2 -MgH 2 during hydrogen sorption are investigated. Differential scanning calorimetry experiments at various H 2 pressures show that the initial decomposition comprises several steps and their transition temperature depends on the applied hydrogen pressure. During the first desorption of the powders, an exothermic phase transition takes place where Mg(NH 2 ) 2 is partially formed. This is followed by an endothermic decomposition that yields hydrogen. The addition of 2 mol% TiCl 3 to the initial 2LiNH 2 -MgH 2 mixture does not affect the exothermic phase transition but the hydrogen release shifts to lower temperatures. Adding 2 mol% TiCl 3 after two hydrogenation cycles to the material has no effect on the desorption properties.