A reversible hydrogen storage mechanism for sodium alanate: the role of alanes and the catalytic effect of the dopant

Walters, R.T.; Scogin, J. H.

doi:10.1016/j.jallcom.2004.04.155

“…8,17 Hwang et al have reported chemical shifts of 5.8, 21.5, and 10.9/36.0 ppm for a-, b-, and g-AlH 3 respectively. 18 Our study is not able to explore this possibility, as the broad resonance at 59 ppm associated with the alumina of the NMR cell will likely Fig.…”

Section: Q4mentioning

confidence: 99%

In situ high pressure NMR study of the direct synthesis of NaAlH4

Humphries

¹

,

Birkmire

²

,

Hauback

³

et al. 2013

Phys. Chem. Chem. Phys.

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The direct synthesis of NaAlH 4 has been studied, for the first time, by in situ 27 Al and 23 Na wide-line NMR spectroscopy using high pressure NMR apparatus. Na 3 AlH 6 formation is observed within two minutes of hydrogenation addition, while NaAlH 4 is detected after a total of four minutes. This indicates the formation of the hexahydride does not proceed to completion before the formation of the tetrahydride ensues.The practical utilization of hydrogen as an energy carrier awaits the development of high-capacity, hydrogen storage materials that can be recharged under moderate conditions. A viable on-board hydrogen carrier must have high gravimetric and volumetric hydrogen capacities; thermodynamic properties that fall within rather stringent limits; and dehydrogenation and rehydrogenation kinetics that allow hydrogen cycling at moderate temperatures and pressures. 1,2 One of the most important breakthroughs in the development of hydrogen storage materials in the past 20 years was provided by Q4Bogdanović and Schwickardi, whose pioneering studies demonstrated that addition of selected titanium compounds to NaAlH 4 results in enhanced kinetics and reversibility under moderate conditions in the solid state. 3 These studies were prompted by earlier reports from Wiberg et al., who observed that titanium compounds catalyze the dehydrogenation of complex aluminum hydrides in solution. 4 The enigmatic extension of this catalytic effect to the solid state has been the inspiration for over 260 publications on Ti-enhanced NaAlH 4 alone, and it is safe to estimate that it prompted an equal number of studies of the effect of Ti additives on the dehydrogenation kinetics of other complex hydrides. 5

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“…[14,15]. The reversible chemical reaction was given as: LiBH 4 + ½ MgH 2  LiH + ½ MgB 2 + 2H 2 (1).…”

Section: Introductionmentioning

confidence: 99%

Fundamental environmental reactivity testing and analysis of the hydrogen storage material 2LiBH4·MgH2

James

¹

,

Brinkman

²

,

Gray

³

et al. 2014

International Journal of Hydrogen Energy

9

0

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While the storage of hydrogen for portable and stationary applications is regarded as critical in bringing PEM fuel cells to commercial acceptance, little is known of the environmental exposure risks posed in utilizing condensed phase chemical storage options as in complex hydrides. It is thus important to understand the effect of environmental exposure of metal hydrides in the case of accident scenarios. Simulated tests were performed following the United Nations standards to test for flammability and water reactivity in air for a destabilized lithium borohydride and magnesium hydride system in a 2 to 1 molar ratio respectively. It was determined that the mixture acted similarly to the parent, lithium borohydride, but at slower rate of reaction seen in magnesium hydride. To quantify environmental exposure kinetics, isothermal calorimetry was utilized to measure the enthalpy of reaction as a function of exposure time to dry and humid air, and liquid water. The reaction with liquid water was found to increase the heat flow significantly during exposure compared to exposure in dry or humid air environments. Calorimetric results showed the maximum normalized heat flow the fully charged material was 6 mW/mg under liquid phase hydrolysis; and 14 mW/mg for the fully discharged material also occurring under liquid phase hydrolysis conditions.

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“…There have been numerous studies focused on understanding the sorption kinetics, hydrogen capacity and structures of the three primary types of complex metal hydrides: alanates [1][2][3], borohydrides [4][5][6], and amides [7][8][9]. However, there is very little understanding of the potential environmental exposure risks associated with implementing these materials.…”

Section: Introductionmentioning

confidence: 99%

Environmental reactivity of solid-state hydrogen storage systems: Fundamental testing and evaluation

James

¹

,

Cortes-Concepcion

²

,

Tamburello

³

et al. 2012

International Journal of Hydrogen Energy

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While the storage of hydrogen for portable and stationary applications is regarded as critical in bringing PEM fuel cells to commercial acceptance, little is known of the environmental exposure risks posed in utilizing condensed phase chemical storage options as in complex hydrides. It is thus important to understand the effect of environmental exposure of metal hydrides in the case of accident scenarios. Simulated tests were performed following the United Nations standards to test for flammability and water reactivity in air for a destabilized lithium borohydride and magnesium hydride system in a 2 to 1 molar ratio respectively. It was determined that the mixture acted similarly to the parent, lithium borohydride, but at slower rate of reaction seen in magnesium hydride. To quantify environmental exposure kinetics, isothermal calorimetry was utilized to measure the enthalpy of reaction as a function of exposure time to dry and humid air, and liquid water. The reaction with liquid water was found to increase the heat flow significantly during exposure compared to exposure in dry or humid air environments. Calorimetric results showed the maximum normalized heat flow the fully charged material was 6 mW/mg under liquid phase hydrolysis; and 14 mW/mg for the fully discharged material also occurring under liquid phase hydrolysis conditions.

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A reversible hydrogen storage mechanism for sodium alanate: the role of alanes and the catalytic effect of the dopant

Cited by 56 publications

References 37 publications

In situ high pressure NMR study of the direct synthesis of NaAlH4

In situ high pressure NMR study of the direct synthesis of NaAlH4

Fundamental environmental reactivity testing and analysis of the hydrogen storage material 2LiBH4·MgH2

Environmental reactivity of solid-state hydrogen storage systems: Fundamental testing and evaluation

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