Hydrogen-Induced Ostwald Ripening at Room Temperature in a Pd Nanocluster Film

Vece, Marcel Di; Grandjean, D.; Bael, M. J. Van; Romero, C.P.; Wang, X; Decoster, Stefan; Vantomme, André; Lievens, Peter

doi:10.1103/physrevlett.100.236105

Cited by 47 publications

(40 citation statements)

References 28 publications

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“…It proceeds more rapidly as temperature increases, which is connected to an enhancement of diffusion rate with rising temperature. In addition to the temperature effect, the grain growth is also facilitated by means of hydrogen-induced Ostwald ripening [43]. An increase of the grain size of about 3 times during hydrogen cycling of Pd films was observed even at room temperature [44].…”

Section: A Temperature Correction Of the Stress-strain Analysismentioning

confidence: 93%

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

2012

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Using hydrogenography, we investigate the thermodynamic parameters and hysteresis behavior in Mg thin films capped by Ta/Pd, in a temperature range from 333 K to 545 K. The enthalpy and entropy of hydride decomposition, ∆H des = −78.3 kJ/molH 2 , ∆S des = −136.1 J/K molH 2 , estimated from the Van't Hoff analysis, are in good agreement with bulk results, while the absorption thermodynamics, ∆H abs = −61.6 kJ/molH 2 , ∆S abs = −110.9 J/K molH 2 , appear to be substantially affected by the clamping of the film to the substrate. The clamping is negligible at high temperatures, T > 523 K, while at lower temperatures, T < 393 K, it is considerable. The hysteresis at room temperature in Mg/Ta/Pd films increases by a factor of 16 as compared to MgH 2 bulk. The hysteresis increases even further in Mg/Pd films, most likely due to the formation of a Mg-Pd alloy at the Mg/Pd interface. The stress-strain analysis of the Mg/Ta/Pd films at 300-333 K proves that the increase of the hysteresis occurs due to additional mechanical work during the (de-)hydrogenation cycle. With a proper temperature correction, our stress-strain analysis quantitatively and qualitatively explains the hysteresis behavior in thin films, as compared to bulk, over the whole temperature range. OPEN ACCESSCrystals 2012, 2 711

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Section: A Temperature Correction Of the Stress-strain Analysismentioning

confidence: 93%

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

2012

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“…The MgH 2 @SNU‐90′ shows the crystal size (diagonal length of hexagon) of average (142±41) nm and thickness of average (83±18) nm (Supporting Information, Figure S12), circa 2.3 times as large as those of Mg NCs. Considering that the volume of Mg should be increased by 30 % on hydride formation,26 this excessive expansion during the H 2 chemisorption processes at high temperature and pressure can be explained by the three‐dimensional Ostwald ripening, in which the larger crystals take up the mobile atoms dissociated from the smaller crystals 27. In addition, degradation of the MOF by electron beam during the TEM measurement plays a role in increasing the size of the MgH 2 crystal.…”

Section: N2 and H2 Gas Uptake Data In Snu‐90′ And Various Samples Of mentioning

confidence: 99%

Magnesium Nanocrystals Embedded in a Metal–Organic Framework: Hybrid Hydrogen Storage with Synergistic Effect on Physi‐ and Chemisorption

et al. 2012

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Hydrogen is considered to be a promising energy carrier for the future. In order to use it as a fuel, a compact, safe, and efficient hydrogen storage system should be developed. Porous metal-organic frameworks (MOFs) have attracted great attention as potential hydrogen storage materials, [1] because some MOFs can store large amount of H 2 (> 7 wt %) at 77 K and high pressures. [2] However, at room temperature, the H 2 storage capacities of MOFs drop to less than 1 wt % because interaction energies between the frameworks and H 2 are very low (4-8 kJ mol À1 ). There have been efforts to enhance the H 2 storage capacities of MOFs at ambient temperature by methods such as tuning the ligand, [3] generation of open metal sites, [4] and embedding palladium nanoparticles. [5] Despite these modifications, the improvements were not very satisfactory, and none of the materials have yet met the target of the US Department of Energy (DOE) of 2017.In search for a highly efficient material for H 2 storage, we have investigated the possibilities of hybrid materials that would be capable of storing H 2 by both physical adsorption and chemisorption. In particular, we have been interested in composite materials that consist of a MOF and magnesium nanoparticles. Magnesium chemisorbs H 2 at 773 K and 200 atm in the presence of MgI 2 catalyst. [6] Magnesium powder of 50-100 mm size made by ball milling slowly absorbs H 2 at 673 K and 10 bar. [7] The resulting magnesium hydride has a quite high dehydrogenation enthalpy ( % 75 kJ per mol H 2 ), [8] and therefore heavy-metal catalysts should be used to reduce the H 2 desorption temperature and improve kinetics, but they still do not allow effective dehydrogenation. [9] In the presence of heavy-metal catalysts, the H 2 absorption and release temperatures decrease as a result of destabilization of the metal hydride when the particle size of magnesium is reduced. [10] Nanosized magnesium particles have been synthesized by a variety of methods, such as ball-milling, [11] condensation of magnesium metal vapor, [12] plasma metal reaction, [13] infiltration of melted Mg in carbon material, [14] and sonoelectrochemistry [15] or chemical reduction of Mg precursors. [16] Some of the disadvantages of these methods are that they require a long process time, extremely high temperatures (898-1203 K), and electrically or chemically harsh conditions, and yet they provide inhomogeneous size distributions.Herein we report a simple method for fabrication of hexagonal-disk-shaped magnesium nanocrystals (Mg NCs) within a MOF. The fabrication of Mg nanocrystals inside MOFs is unprecedented. Previously, small Ag, Au, Ni, Pd, Ru, or Pt nanoparticles (size, 1.4-10 nm) were prepared in MOFs by immersing redox-active MOFs in the metal-ion solutions [5,17] or by reducing the metal precursors deposited in the MOFs. [18] The present nanocomposite is made by the thermal decomposition of air-sensitive bis-cyclopentadienyl magnesium (MgCp 2 ) vapor in a MOF, leading to the deposition of MG NCs in the MOF, a method t...

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“…7 However, this phenomenon is not restricted to high temperatures alone but can also be observed by exposing palladium nanoclusters to hydrogen. 8 Hydrogen-induced Ostwald ripening is the result of a decreasing sublimation energy upon hydrogenation, which stimulates the detachment of atoms from the clusters at room temperature. This raises the question of how hydrogen would influence a bimetallic hydrogen absorbing nanocluster.…”

Section: Introductionmentioning

confidence: 99%

Compositional changes of Pd-Au bimetallic nanoclusters upon hydrogenation

et al. 2009

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Changes in the size distribution and composition of bimetallic Pd-Au nanoclusters have been observed after hydrogen exposure. This effect is caused by hydrogen-induced Ostwald ripening whereby the hydrogen reduces the binding energy of the cluster atoms leading to their detachment from the cluster. The composition changes due to a difference in mobility of the detached palladium and gold atoms on the surface. Fast palladium atoms contribute to the formation of larger nanoclusters, while the slower gold atoms are confined to the smaller nanoclusters. These transformations in the Pd-Au nanocluster size and composition set a limit for chemical reactions in which such nanoclusters are involved together with hydrogen.

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Hydrogen-Induced Ostwald Ripening at Room Temperature in a Pd Nanocluster Film

Cited by 47 publications

References 28 publications

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

Magnesium Nanocrystals Embedded in a Metal–Organic Framework: Hybrid Hydrogen Storage with Synergistic Effect on Physi‐ and Chemisorption

Compositional changes of Pd-Au bimetallic nanoclusters upon hydrogenation

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