Characterization of NH3 formation in desorption of Li–Mg–N–H storage system

Widespread adoption of hydrogen as a vehicular fuel depends critically upon the ability to store hydrogen on-board at high volumetric and gravimetric densities, as well as on the ability to extract/insert it at sufficiently rapid rates. As current storage methods based on physical means-high-pressure gas or (cryogenic) liquefaction-are unlikely to satisfy targets for performance and cost, a global research effort focusing on the development of chemical means for storing hydrogen in condensed phases has recently emerged. At present, no known material exhibits a combination of properties that would enable high-volume automotive applications. Thus new materials with improved performance, or new approaches to the synthesis and/or processing of existing materials, are highly desirable. In this critical review we provide a practical introduction to the field of hydrogen storage materials research, with an emphasis on (i) the properties necessary for a viable storage material, (ii) the computational and experimental techniques commonly employed in determining these attributes, and (iii) the classes of materials being pursued as candidate storage compounds. Starting from the general requirements of a fuel cell vehicle, we summarize how these requirements translate into desired characteristics for the hydrogen storage material. Key amongst these are: (a) high gravimetric and volumetric hydrogen density, (b) thermodynamics that allow for reversible hydrogen uptake/release under near-ambient conditions, and (c) fast reaction kinetics. To further illustrate these attributes, the four major classes of candidate storage materials-conventional metal hydrides, chemical hydrides, complex hydrides, and sorbent systems-are introduced and their respective performance and prospects for improvement in each of these areas is discussed. Finally, we review the most valuable experimental and computational techniques for determining these attributes, highlighting how an approach that couples computational modeling with experiments can significantly accelerate the discovery of novel storage materials (155 references).

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“…More rigorous methods such as Draeger Tube tests (for NH 3 detection) are often used for sensitive quantification of trace gases. 150 …”

Section: Puritymentioning

confidence: 99%

High capacity hydrogenstorage materials: attributes for automotive applications and techniques for materials discovery

et al. 2010

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“…The unmodified mixture lost a total of 10.94 wt% during decomposition, which is significantly higher than the theoretical hydrogen capacity of 8.14 wt%. This increase is attributed to release of ammonia from the decomposition of unreacted LiNH 2 and the slow reaction kinetics between MgH 2 and NH 3 [17,18].…”

Section: Decomposition Of the Modified And Unmodified Systemsmentioning

confidence: 99%

“…One issue related to the application of metal-N-H storage systems is ammonia formation that takes place simultaneously with H 2 release [16,17]. Through the use of Draeger tubes on the 2:1 LiNH 2 :MgH 2 system, Luo et al showed that ammonia concentration was strongly dependent on the desorption temperature with concentrations of 180ppm measured at 180°C and 720ppm at 240°C [17].…”

mentioning

confidence: 99%

“…Through the use of Draeger tubes on the 2:1 LiNH 2 :MgH 2 system, Luo et al showed that ammonia concentration was strongly dependent on the desorption temperature with concentrations of 180ppm measured at 180°C and 720ppm at 240°C [17]. In a separate analysis, the effect of milling duration on ammonia release from the 2:1 mixture during heating was investigated, resulting in over 30 ppm/mg for unmilled samples and under 10 ppm/mg fo samples milled for 180 minutes using high-energy milling [18].…”

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confidence: 99%

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The effects of halide modifiers on the sorption kinetics of the Li-Mg-N-H System

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et al. 2012

International Journal of Hydrogen Energy

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The effects of different transition metal halides (TiCl 3 , VCl 3 , ScCl 3 and NiCl 2 ) on the sorption properties of the 1:1 molar ratio of LiNH 2 to MgH 2 are investigated. The modified mixtures were found to contain LiNH 2 , MgH 2 and LiCl. TGA results showed that the hydrogen desorption temperature was reduced with the modifier addition in this order: TiCl 3 > ScCl 3 > VCl 3 > NiCl 2 . Ammonia release was not significantly reduced resulting in a weight loss greater than the theoretical hydrogen storage capacity of the material. The isothermal sorption kinetics of the modified systems showed little improvement after the first dehydrogenation cycle over the unmodified system but showed drastic improvement in rehydrogenation cycles. X-ray diffraction and Raman spectroscopy identified the cycled material to be composed of LiH, MgH 2 , Mg(NH 2 ) 2 and Mg 3 N 2 .

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“…In the first dehydrogenation cycle, the desorption rate is significantly slower than the subsequent three runs, ascribable to the fact that, in the first one, there is an interaction between the LiNH 2 and MgH 2 . The sorption mechanism, summarized in Figure 4, has been further investigated by Sickafoose et al [54] In the first step of the isotherm, one hydrogen atom is inserted into the Li 2 Luo et al [55,56] determined the NH 3 emission in the desorption step of the 2LiNH 2 + MgH 2 system. The results indicate that the NH 3 concentration is around 180 ppm at 180 • C and 720 ppm at 240 • C, restricting the cycling and then the applicability.…”

Section: Li-mg-n-h Systemmentioning

confidence: 99%

Recent Progress and New Perspectives on Metal Amide and Imide Systems for Solid-State Hydrogen Storage

et al. 2018

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Hydrogen storage in the solid state represents one of the most attractive and challenging ways to supply hydrogen to a proton exchange membrane (PEM) fuel cell. Although in the last 15 years a large variety of material systems have been identified as possible candidates for storing hydrogen, further efforts have to be made in the development of systems which meet the strict targets of the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) and U.S. Department of Energy (DOE). Recent projections indicate that a system possessing: (i) an ideal enthalpy in the range of 20-50 kJ/mol H 2 , to use the heat produced by PEM fuel cell for providing the energy necessary for desorption; (ii) a gravimetric hydrogen density of 5 wt. % H 2 and (iii) fast sorption kinetics below 110 • C is strongly recommended. Among the known hydrogen storage materials, amide and imide-based mixtures represent the most promising class of compounds for on-board applications; however, some barriers still have to be overcome before considering this class of material mature for real applications. In this review, the most relevant progresses made in the recent years as well as the kinetic and thermodynamic properties, experimentally measured for the most promising systems, are reported and properly discussed.

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Characterization of NH3 formation in desorption of Li–Mg–N–H storage system

Cited by 48 publications

References 15 publications

High capacity hydrogenstorage materials: attributes for automotive applications and techniques for materials discovery

High capacity hydrogenstorage materials: attributes for automotive applications and techniques for materials discovery

The effects of halide modifiers on the sorption kinetics of the Li-Mg-N-H System

Recent Progress and New Perspectives on Metal Amide and Imide Systems for Solid-State Hydrogen Storage

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