Ammonia for hydrogen storage: challenges and opportunities

Klerke, Asbjørn; Christensen, Claus H.; Nørskov, Jens K.; Vegge, Tejs

doi:10.1039/b720020j

Cited by 1,131 publications

(700 citation statements)

References 63 publications

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“…Having confirmed this replacement by QMS, the fixed bed was heated at a rate of 10 K·min −1 up to the designated holding temperature, which was maintained for at least 2 h to complete the reduction reaction. The gas was then replaced by pure argon at a rate of 200 cm 3 ·min −1 at standard temperature and pressure (STP). Finally, the fixed bed was cooled down to ambient temperature.…”

Section: Methodsmentioning

confidence: 99%

“…2) Ammonia, which has a high hydrogen content, has attracted considerable interest in recent years as a potential hydrogen transport medium. [3][4][5][6] The storage density of ammonia is 17.6 mass% or 120 kg/m 3 for liquid NH 3 , considerably higher than for most advanced metal hydrides. Ammonia gas is relatively easy to liquefy (240 K at 101 kPa) compared with hydrogen gas (140 K at 101 kPa).…”

Section: Introductionmentioning

confidence: 94%

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Reduction and Nitriding Behavior of Hematite with Ammonia

et al. 2015

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This paper describes the reduction and nitriding behavior of hematite with ammonia in the context of ironmaking. The effects of temperature and ammonia concentration on the products were investigated. In the temperature range from 793 to 863 K, hematite was directly reduced to magnetite by ammonia (1/2Fe2O3 + 1/9NH3 → 1/3Fe3O4 + 1/6H2O + 1/18N2). The ammonia started to decompose at 873 K, triggered by the generation of α-Fe. Magnetite was reduced mainly to iron by hydrogen generated from the decomposition of ammonia (1/3Fe3O4 + 4/3H2 → Fe + 4/3H2O). According to in-situ X-ray diffraction (XRD) measurements, α-Fe was immediately nitrided to an ε-Fe 3-x N (0 ≤ x ≤ 1) phase, and the N/Fe atomic ratio decreased gradually with increasing temperatures. The rate of hematite reduction increased with the ammonia concentration for 5% to 20% NH3, but plateaus for NH3 concentrations greater than 20%. This was attributed to the mechanism of ammonia decomposition; the amount of hydrogen generated also plateaus at ammonia concentrations above 20%. The reduction rate was therefore limited by the rate at which hydrogen was generated during ammonia decomposition. The N content of the product was affected not only by the temperature but also by the nitriding potential (KN = P NH 3 /P H 2 3/2 ). The nitriding potential increased with increasing ammonia concentrations and decreasing temperatures. The addition of nitrogen gas to the reactive gas inhibited ammonia decomposition and increased the nitrogen potential and N content of the product.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 94%

Reduction and Nitriding Behavior of Hematite with Ammonia

et al. 2015

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“…Additionally, NH 3 is an energy carrier formed via reduction of N 2 , analogous to the products of photosynthesis, such as CO and hydrocarbon fuels via reduction of CO 2 and splitting of H 2 O. Thus, NH 3 may find application as a hydrogen carrier [9,10] and as a fuel for alkaline fuel cells [11,12] and in internal combustion engines [13,14] (http://nh3fuelassociation.org/2013/06/20/the-amveh-an-ammoniafueled-car-from-south-korea/). Currently, NH 3 is produced industrially from N 2 and H 2 via the catalytic Haber-Bosch process at up to 300 bar and 400-5008C [7,[15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

2015

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Fixed nitrogen is an essential chemical building block for plant and animal protein, which makes ammonia (NH 3 ) a central component of synthetic fertilizer for the global production of food and biofuels. A global project on artificial photosynthesis may foster the development of production technologies for renewable NH 3 fertilizer, hydrogen carrier and combustion fuel. This article presents an alternative path for the production of NH 3 from nitrogen, water and solar energy. The process is based on a thermochemical redox cycle driven by concentrated solar process heat at 700–1200°C that yields NH 3 via the oxidation of a metal nitride with water. The metal nitride is recycled via solar-driven reduction of the oxidized redox material with nitrogen at atmospheric pressure. We employ electronic structure theory for the rational high-throughput design of novel metal nitride redox materials and to show how transition-metal doping controls the formation and consumption of nitrogen vacancies in metal nitrides. We confirm experimentally that iron doping of manganese nitride increases the concentration of nitrogen vacancies compared with no doping. The experiments are rationalized through the average energy of the dopant d-states, a descriptor for the theory-based design of advanced metal nitride redox materials to produce sustainable solar thermochemical ammonia.

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“…A great deal of attention has been paid to the chemical storage of hydrogen, and various types of hydrogen storage systems have been intensively studied based on different hydrogen carriers such as metal and organic hydrides [10][11][12][13][14]. Ammonia [15][16][17][18][19][20] has recently been widely accepted as a very promising and important hydrogen carrier owing to its fascinating properties. First, ammonia has a very high mass storage capacity (17.6 wt %) and can be easily stored as a liquid under mild conditions that equate to an extremely high volumetric hydrogen storage density of 108 g/L, which is much higher than that of liquid hydrogen (71 g/L) [16].…”

Section: Introductionmentioning

confidence: 99%

Catalytic Ammonia Decomposition over High-Performance Ru/Graphene Nanocomposites for Efficient COx-Free Hydrogen Production

Kanezashi

Tsuru

2017

Catalysts

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Highly-dispersed Ru nanoparticles were grown on graphene nanosheets by simultaneously reducing graphene oxide and Ru ions using ethylene glycol (EG), and the resultant Ru/graphene nanocomposites were applied as a catalyst to ammonia decomposition for CO x -free hydrogen production. Tuning the microstructures of Ru/graphene nanocomposites was easily accomplished in terms of Ru particle size, morphology, and loading by adjusting the preparation conditions. This was the key to excellent catalytic activity, because ammonia decomposition over Ru catalysts is structure-sensitive. Our results demonstrated that Ru/graphene prepared using water as a co-solvent greatly enhanced the catalytic performance for ammonia decomposition, due to the significantly improved nano architectures of the composites. The long-term stability of Ru/graphene catalysts was evaluated for CO x -free hydrogen production from ammonia at high temperatures, and the structural evolution of the catalysts was investigated during the catalytic reactions. Although there were no obvious changes in the catalytic activities at 450 • C over a duration of 80 h, an aggregation of the Ru nanoparticles was still observed in the nanocomposites, which was ascribed mainly to a sintering effect. However, the performance of the Ru/graphene catalyst was decreased gradually at 500 • C within 20 h, which was ascribed mainly to both the effect of the methanation of the graphene nanosheet under a H 2 atmosphere and to enhanced sintering under high temperatures.

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Ammonia for hydrogen storage: challenges and opportunities

Cited by 1,131 publications

References 63 publications

Reduction and Nitriding Behavior of Hematite with Ammonia

Reduction and Nitriding Behavior of Hematite with Ammonia

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

Catalytic Ammonia Decomposition over High-Performance Ru/Graphene Nanocomposites for Efficient COx-Free Hydrogen Production

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