Size effects on the hydrogen storage properties of nanostructured metal hydrides: A review

Bérubé, Vincent; Radtke, Gregg Arthur; Dresselhaus, M. S.; Chen, Gang

doi:10.1002/er.1284

Cited by 577 publications

(195 citation statements)

References 84 publications

Supporting

Mentioning

161

Contrasting

Unclassified

Order By: Relevance

“…In this process, the rate-limiting step changes from the dissociation and penetration of hydrogen at the metal/H 2 interface to the nucleation of the hydride phase, and possibly the diffusion of hydrogen through the metal hydride layer that forms around the metal particle. 54 We expect to see similar processes in Li 2 NH.…”

Section: Hydrogenation Of Li2nhmentioning

confidence: 83%

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

2012

View full text Add to dashboard Cite

Reversible reaction involving Li amide (LiNH2) and Li imide (Li2NH) is a potential mechanism for hydrogen storage. Recent synchrotron x-ray diffraction experiments [W. I. David et al., J. Am. Chem. Soc. 129, 1594] suggest that the transformation between LiNH2 and Li2NH is a bulk reaction that occurs through non-stoichiometric processes and involves the migration of Li + and H + ions. In order to understand the atomistic mechanisms behind these processes, we carry out comprehensive first-principles studies of native point defects and defect complexes in the two compounds. We find that both LiNH2 and Li2NH are prone to Frenkel disorder on the Li sublattice. Lithium interstitials and vacancies have low formation energies and are highly mobile, and therefore play an important role in mass transport and ionic conduction. Hydrogen interstitials and vacancies, on the other hand, are responsible for forming and breaking N−H bonds, which is essential in the Li amide/imide reaction. Based on the structure, energetics, and migration of hydrogen-, lithium-, and nitrogen-related defects, we propose that LiNH2 decomposes into Li2NH and NH3 according to two competing mechanisms with different activation energies: one mechanism involves the formation of native defects in the interior of the material, the other at the surface. As a result, the prevailing mechanism and hence the effective activation energy for decomposition depend on the surface-tovolume ratio or the specific surface area, which changes with particle size during ball milling. These mechanisms also provide an explanation for the dehydrogenation of LiNH2+LiH mixtures.

show abstract

Section: Hydrogenation Of Li2nhmentioning

confidence: 83%

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

2012

View full text Add to dashboard Cite

show abstract

“…Fortunately, systematic studies (11-13) of the evolution of desorption energies and electronic structure of Mg n H 2n clusters as a function of n have shown that the properties have converged when n is Ϸ30. Therefore, a 31 formula unit MgH 2 nanocluster was used in the present work to study the effect of doping in nanostructures; and given the recent advances in synthesis of nanoscale particles (14) and the move in the hydrogen storage community toward highly nanostructured hydrogen storage materials (15), clusters of the size considered here may soon become more than model systems.…”

Section: Mgh 2 Cluster Modelmentioning

confidence: 99%

Role of catalysts in dehydrogenation of MgH ₂ nanoclusters

Larsson

Araújo

Larsson

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

A fundamental understanding of the role of catalysts in dehydrogenation of MgH2 nanoclusters is provided by carrying out firstprinciples calculations based on density functional theory. It is shown that the transition metal atoms Ti, V, Fe, and Ni not only lower desorption energies significantly but also continue to attract at least four hydrogen atoms even when the total hydrogen content of the cluster decreases. In particular, Fe is found to migrate from the surface sites to the interior sites during the dehydrogenation process, releasing more hydrogen as it diffuses. This diffusion mechanism may account for the fact that a small amount of catalysts is sufficient to improve the kinetics of MgH2, which is essential for the use of this material for hydrogen storage in fuel-cell applications.hydrogen storage ͉ transition metals ͉ diffusion ͉ catalysis T here is an increasing trend in the use of fuel cells in vehicles (1, 2) and as replacement for batteries in mobile phones and laptop computers (3, 4). In recent years, complex light metal hydrides (5, 6) have attracted considerable attention as hydrogen storage materials because of their large gravimetric density. The metal-hydrogen bonds in these materials are strong, however, and the poor kinetics and thermodynamics do not make these materials suitable for mobile applications. Therefore, the primary focus of research has been to find ways to improve the kinetic and thermodynamic behavior of these light metal hydrides by weakening the metal-hydrogen bond. Although the high thermodynamic stability [⌬H ϭ Ϫ75 kJ (mol H 2 ) Ϫ1 ] and dissociation temperature (Ϸ400°C) combined with poor kinetics impede the use of MgH 2 for hydrogen storage, it does possess some attractive features. First, it is a low-cost material because of the abundantly available magnesium. Second, it has a gravimetric density of 7.7 wt % and, unlike the alanates, all of this hydrogen can be desorbed. Third, being a binary alloy, the role of catalysts is easier to study than in the ternary alanates. The current research on MgH 2 has focused on reducing the strength of the metal-hydrogen bond by nanostructuring and/or using catalysts. It has been shown that mechanical ball milling can reduce the particle size to Ϸ10 nm where defects, large surface areas, and grain boundaries help to improve the kinetics and thermodynamics of hydrogen sorption (7). Further milling with transition metal additives such as Ti, V, Fe, Co, and Ni leads to greatly enhanced hydrogen sorption kinetics (8-10). Despite a considerable amount of experimental work, a fundamental understanding of how nanostructuring and/or catalysts improve the kinetics and thermodynamics of MgH 2 is still lacking. It is needless to emphasize that an understanding of where the catalytic atoms reside and how a small amount of catalysts can improve the thermodynamic behavior is necessary for the synthesizing of materials with optimal performance. Here, an attempt to provide such an understanding is made by carrying out first-principles calculations o...

show abstract

“…However, the temperature for releasing hydrogen still remains far above the requirements for ambient condition applications. Moreover, a major drawback of this approach is that it is accompanied by a significant reduction of the storage capacity [5]. Recent studies have shown that hydrogen adsorbed on nanostructured Mg can be released at a low temperature and it can be even significantly lowered if other compounds such as carbon nanotubes are added to the material [6].…”

Section: Introductionmentioning

confidence: 99%

First-principles studies of hydrogen interaction with ultrathin Mg and Mg-based alloy films

2011

View full text Add to dashboard Cite

The search for technologically and economically viable storage solutions for hydrogen fuel would greatly benefit from research strategies that involve systematic property tuning of potential storage materials via atomic-level modification. Here, we use first-principles density functional theory (DFT) to theoretically investigate the structural and electronic properties of ultrathin Mg films and Mg-based alloy films and their interaction with atomic hydrogen.Additional delocalized charges are distributed over the Mg films upon alloying them with 11.1% of Al or Na atoms. These extra charges contribute to enhance the hydrogen binding strength to the films. We calculated the chemical potential of hydrogen in Mg films for different dopant species and film thickness, and included the vibrational degrees of freedom. By comparing the chemical potential with that of free hydrogen gas at finite temperature (T) and pressure (P), we construct a hydrogenation phase diagram and identify the conditions for hydrogen absorption/desorption. The formation enthalpies of metal hydrides are greatly increased in thin films, and in stark contrast to its bulk phase, the hydride state can only be stabilized at high P and T (where chemical potential of free H 2 is very high). Metal-doping increases the thermodynamic stabilities of the hydride films and thus significantly helps to reduce the required pressure condition for hydrogen absorption from H 2 gas. In particular, with Na alloying hydrogen can be absorbed/desorbed at experimentally accessible T and P conditions.

show abstract

Size effects on the hydrogen storage properties of nanostructured metal hydrides: A review

Cited by 577 publications

References 84 publications

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

Role of catalysts in dehydrogenation of MgH ₂ nanoclusters

First-principles studies of hydrogen interaction with ultrathin Mg and Mg-based alloy films

Contact Info

Product

Resources

About

Size effects on the hydrogen storage properties of nanostructured metal hydrides: A review

Cited by 577 publications

References 84 publications

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

Mechanisms for the decomposition and dehydrogenation of Li amide/imide

Role of catalysts in dehydrogenation of MgH 2 nanoclusters

First-principles studies of hydrogen interaction with ultrathin Mg and Mg-based alloy films

Contact Info

Product

Resources

About

Role of catalysts in dehydrogenation of MgH ₂ nanoclusters