Hydrogen Cycling of Niobium and Vanadium Catalyzed Nanostructured Magnesium

Schimmel, H. Gijs; Huot, Jacques; Chapon, L. C.; Tichelaar, F.D.; Mulder, Fokko M.

doi:10.1021/ja051508a

Cited by 227 publications

(196 citation statements)

References 33 publications

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“…The crystal structure of magnesium is hexagonal close packing and the calculated Mg bulk lattice constants are a Mg = b Mg = 3.190Å with the c/a value of 1.623, which are in good agreement with the experimental values 48,49 and previous theoretical results. [50][51][52] Magnesium hydride, whose crystal structure is simple tetragonal, is a highly stable hydride with strong Mg-H bond, which is a mixture of ionic and covalent bonding.…”

Section: A the Bulk Properties Of Magnesium And Magnesium Hydridesupporting

confidence: 88%

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

et al. 2014

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We have theoretically investigated the modeling and the structural stabilities of various Mg/MgH2 interfaces, i.e. Mg($10\bar 10$101¯0)/MgH2(210), Mg(0001)/MgH2(101) and Mg($10\bar 10$101¯0)/MgH2(101), and provided illuminating insights into Mg/MgH2 interface. Specifically, the main factors, which impact the interfacial energies, are fully considered, including surface energies of two phases, mutual lattice constants of interface model, and relative position of two phases. The surface energies of Mg and MgH2, on the one hand, are found to be greatly impacting the interfacial energies, reflected by the lowest interfacial energy of Mg(0001)/MgH2(101) which is comprised of two lowest energy surfaces. On the other hand, it is demonstrated that the mutual lattice constants and the relative position of two phases lead to variations of interfacial energies, thus influencing the interface stabilities dramatically. Moreover, the Mg-H bonding at interface is found to be the determinant of Mg/MgH2 interface stability. Lastly, interfacial and strain effects on defect formations are also studied, both of which are highly facilitating the defect formations. Our results provide a detailed insight into Mg/MgH2 interface structures and the corresponding stabilities.

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Section: A the Bulk Properties Of Magnesium And Magnesium Hydridesupporting

confidence: 88%

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

et al. 2014

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“…6 On the other hand, Mg−Nb−O perovskite phase was also found in the dehydrogenated composite and believed to help with hydrogen transportation. 7 Transition-metal oxides also show the catalytic effect on facilitating hydrogen absorption and desorption in nanostructured MgH 2 . 8−13 Among those catalysts studied so far, Nb 2 O 5 showed a superior catalytic effect.…”

Section: ■ Introductionmentioning

confidence: 99%

Nb-Gateway for Hydrogen Desorption in Nb₂O₅ Catalyzed MgH₂ Nanocomposite

Isobe

Wang

et al. 2013

J. Phys. Chem. C

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The state of Nb-contained catalysts in MgH 2 nanocomposites was investigated during the full cycle. X-ray diffraction (XRD) results showed that Nb 2 O 5 and Nb reacted with MgH 2 during ball-milling, forming NbH 2 and NbH, respectively. In the following dehydrogenation, the (di)hydride decomposed, and Nb was produced. Then NbH was generated in both samples after rehydrogenation. Similar composition in both samples suggests that the catalytic effect follows the same mechanism, the Nb-gateway model, in which Nb facilitates the hydrogen transportation from MgH 2 to the outside. By contrast, NbO remained during the full cycle. Scanning and transmission electron microscopy (SEM and TEM) observations revealed that the Nb 2 O 5 -doped sample tended to be refined in size, compared to the Nb-doped and NbO-doped ones. Nb crystals in the Nb 2 O 5 -doped sample were observed to be highly dispersed in the sample, with 10−20 nm in size. Given all that, tiny Nb crystals distributed in the composites worked as the gateway facilitating hydrogen transportation and improving dehydrogenation properties. ■ INTRODUCTIONHydrogen is a promising alternative energy carrier because of its prominent advantages such as high energy density, great variety of potential sources, light weight, and environmental friendliness; thus it has been highly regarded. As a medium for hydrogen storage, magnesium hydride has been well studied in the past decades. Having notable advantages such as high capacity (7.6 mass %), light weight, and low cost, it is considered as a promising candidate for hydrogen storage materials.1 However, the absorption and desorption processes require high temperatures of 300−400°C, and the reactions are slow. By ball-milling with some transition metals, the kinetics of the reactions can be improved.2−4 Huot et al. showed the result that MgH 2 nanoparticles catalyzed by 5 mol % Nb completed full desorption within 300 s at 300°C. 4 They confirmed the formation of a short-lived metastable NbH x (x ≈ 0.6) phase during dehydrogenation, thus concluded that it acted as a gateway through which hydrogen from MgH 2 released. 5 A similar mechanism was claimed later by Li et al. in a density functional theory calculation, in which the substitution of Nb at the Mg site followed by the clustering of H around Nb was a likely pathway for hydrogen desorption. 6 On the other hand, Mg−Nb−O perovskite phase was also found in the dehydrogenated composite and believed to help with hydrogen transportation. Transition-metal oxides also show the catalytic effect on facilitating hydrogen absorption and desorption in nanostructured MgH 2 .8−13 Among those catalysts studied so far, Nb 2 O 5 showed a superior catalytic effect. Barkhordarian et al. reported that MgH 2 catalyzed by 0.5 mol % Nb 2 O 5 and ballmilled for 100 h finished desorption within 90 s at 300°C. 10Hanada et al. reported that the composite, MgH 2 and 1 mol % Nb 2 O 5 milled for 20 h, was able to absorb ∼4.5 wt % of hydrogen after full desorption, under a pressure of 1.0 MPa wit...

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“…The latter can be substantially increased using small grain sizes 1 and adding transition metals or their oxides. In particular, niobium 2 and palladium 3,4 have a pronounced impact on the sorption kinetics. Previous studies [4][5][6] showed that spark discharge generation (SDG) is a versatile method for the production of metal nanoparticles.…”

mentioning

confidence: 99%

Fractal disperse hydrogen sorption kinetics in spark discharge generated Mg/NbOx and Mg/Pd nanocomposites

Anastasopol

Pfeiffer

Schmidt‐Ott

et al. 2011

Applied Physics Letters

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Isothermal hydrogen desorption of spark discharge generated Mg/NbO x and Mg/Pd metal hydride nanocomposites is consistently described by a kinetic model based on multiple reaction rates, in contrast to the Johnson-Mehl-Avrami-Kolmogorov [M. Avrami, J. Phys. Chem. 9, 177 (1941); W. A. Johnson and R. F. Mehl, Trans. Am. Inst. Min., Metal. Eng. 135, 416 (1939); A. N. Kolmogorov, Izv. Akad. Nauk SSSR, Ser. Mat. 3, 355 (1937); F. Liu, F. Sommer, C. Bos, and E. J. Mittemeijer, Int. Mat. Rev. 52, 193 (2007)] model which is commonly applied to explain the kinetics of metal hydride transformations. The broad range of reaction rates arises from the disperse character of the particle size and the dendritic morphology of the samples. The model is expected to be generally applicable for metal hydrides which show a significant variation in particle sizes, in configuration and/or chemical composition of local surroundings of the reacting nanoparticles. In the context of hydrogen storage, MgH 2 remains an attractive candidate despite its relatively high stability and slow sorption kinetics. The latter can be substantially increased using small grain sizes 1 and adding transition metals or their oxides. In particular, niobium 2 and palladium 3,4 have a pronounced impact on the sorption kinetics. Previous studies [4][5][6] showed that spark discharge generation (SDG) is a versatile method for the production of metal nanoparticles. In particular, the onset of hydrogen desorption of spark discharge produced MgH 2 nanoparticles loaded from the gas phase occurs at a rather low temperature of $400 K. 5 The hydrogen desorption is characterized by a broad desorption profile, which could be explained in terms of multiple apparent activation energies.Here, we present a systematic study of the isothermal hydrogen desorption kinetics of spark discharge Mg/NbO x and Mg/Pd nanocomposites loaded from the gas phase. We found that a kinetic model based on multiple reaction rates within the sample can consistently describe the results from our studies, in contrast to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, 7-10 applied to metal hydride transformation kinetics, and explains the transformation as a homogeneous nucleation and growth process. The broad range of reaction rates arises from the disperse character of the particle size distribution and the dendritic morphology of the SDG samples.A dual spark generator setup 5 was used for the production of Mg nanoparticles and for the intermixing with spark discharge generated Pd or Nb catalyst particles in-situ in the spark discharge reactor. The frequency of the 40 mJ Mg sparks is 300 Hz. In order to produce a targeted amount of a few at. % of catalyst, the second spark is operated with 14 mJ pulses at a frequency of 34 Hz. The samples were loaded in a hermetically closed sample holder in an Ar glovebox. Transmission electron microscopy (TEM) was performed on a FEI TECNAI TF20 monochromatic electron microscope at 200 kV. The x-ray diffraction (XRD) was performed using a Panalytical X'pert Pro ...

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Hydrogen Cycling of Niobium and Vanadium Catalyzed Nanostructured Magnesium

Cited by 227 publications

References 33 publications

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

Nb-Gateway for Hydrogen Desorption in Nb₂O₅ Catalyzed MgH₂ Nanocomposite

Fractal disperse hydrogen sorption kinetics in spark discharge generated Mg/NbOx and Mg/Pd nanocomposites

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Hydrogen Cycling of Niobium and Vanadium Catalyzed Nanostructured Magnesium

Cited by 227 publications

References 33 publications

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

Modeling and stabilities of Mg/MgH2 interfaces: A first-principles investigation

Nb-Gateway for Hydrogen Desorption in Nb2O5 Catalyzed MgH2 Nanocomposite

Fractal disperse hydrogen sorption kinetics in spark discharge generated Mg/NbOx and Mg/Pd nanocomposites

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Nb-Gateway for Hydrogen Desorption in Nb₂O₅ Catalyzed MgH₂ Nanocomposite