Diffusion of deuterium and hydrogen in doped and undoped MgO crystals

González, R.; Chen, Y.; Tsang, K. L.

doi:10.1103/physrevb.26.4637

Cited by 73 publications

(36 citation statements)

References 31 publications

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“…They are similar to the spectra for MgO reported previously (e.g., Bolfan-Casanova et al 2000;Demouchy et al 2007;Gonzalez et al 1982). The spectra of H-bearing samples indicate two types of absorption bands: First type includes a strong absorption band at 3,296 cm −1 and weaker bands at 3,310, 3,373, and 3,466 cm −1 while the second type around 3,700 cm −1 .…”

Section: Experimental Conditions and The Redox Environmentsupporting

confidence: 77%

“…Vacancy diffusivity is discussed later ("Discussions" section). Hydrogen diffusivity in MgO was determined as ~1 × 10 −10 m 2 /s at 1,873 K with activation energy of ~180 kJ/mol (Gonzalez et al 1982) (we assume the activation volume of 2 cm 3 /mol). Then, the diffusion length for those point defects during the experiments reaches more than the half thickness of the sample.…”

Section: Experimental Conditions and The Redox Environmentmentioning

confidence: 99%

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The influence of ferric iron and hydrogen on Fe–Mg interdiffusion in ferropericlase ((Mg,Fe)O) in the lower mantle

Otsuka

Karato

2014

Phys Chem Minerals

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are reasonably consistent with values estimated from previous experimental and theoretical studies.Abstract Both ferric iron (Fe 3+ ) and hydrogen (H + ) have important influence on several transport properties of minerals such as diffusion. We determined the influence of Fe 3+ and H + on Fe-Mg interdiffusion in (Mg,Fe) O at 1,673-1,873 K and 5-24 GPa under the anhydrous and hydrous conditions using the diffusion couple technique. The diffusion couples consist of single crystals of ferropericlase ((Mg,Fe)O) and periclase (MgO) with Mg/ (Mg + Fe) ratios ranging from 0.44 to 1.0. The oxygen fugacity was controlled by the following assemblages of metal and oxide: Fe-FeO, Ni-NiO, Mo-MoO 2 , and ReReO 2 . After the diffusion experiments, hydrogen (H + ) concentrations were measured using the FTIR spectroscopy. Fe 3+ concentrations were measured using the flank method. Under the conditions investigated, Fe-Mg interdiffusivity increases strongly with Fe 3+ and modestly with H + and the influence of H + relative to that of Fe 3+ on Fe-Mg interdiffusion decreases with temperature. Our results show that, under both anhydrous and hydrous conditions, the dominant defect responsible for diffusion is the same suggesting that H + enhances Fe-Mg interdiffusivity by enhancing the mobility of vacancies at the M-site. Our results indicate that the influence of Fe 3+ likely dominates at temperatures expected for the normal lower mantle conditions (T > 1,900 K), while the influence of both Fe 3+ and H + is important at lower temperature environments such as near the subduction zone. We also estimated the vacancy diffusivity based on Fe-Mg interdiffusion and vacancy concentration estimated from the charge neutrality condition with Fe 3+ . Both Fe-Mg interdiffusivity and vacancy diffusivities

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Section: Experimental Conditions and The Redox Environmentsupporting

confidence: 77%

Section: Experimental Conditions and The Redox Environmentmentioning

confidence: 99%

The influence of ferric iron and hydrogen on Fe–Mg interdiffusion in ferropericlase ((Mg,Fe)O) in the lower mantle

Otsuka

Karato

2014

Phys Chem Minerals

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“…MgO is expected to act as a barrier between bulk MgH 2 , gas phase and Ni, due to its dense rock-salt structure limiting the diffusion of H 2 atoms [59,60]. For both samples investigated diffusion of atomic H 2 through Mg/MgH 2 and MgO is contributing to the overall rate, whereas two-dimensional surface diffusion of H on MgO is assumed to have negligible activation energy and thus a high rate.…”

Section: The Influence Of Surface Oxidationmentioning

confidence: 99%

Dehydrogenation kinetics of pure and nickel-doped magnesium hydride investigated by in situ time-resolved powder X-ray diffraction

Jensen

Andreasen

Vegge

et al. 2006

International Journal of Hydrogen Energy

148

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“…It was pointed out that MgO is almost impermeable for hydrogen. 23 The Mg− Nb−O phase was proved able to absorb hydrogen 24 and even improve desorption properties of MgH 2 as a catalyst. 25 Here the existence of MgNb 2 O 3.67 may provide pathways for hydrogen diffusion through the MgO scale covered on the surface of MgH 2 , improving the desorption properties during dehydrogenation.…”

Section: ■ Experimental Sectionmentioning

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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Diffusion of deuterium and hydrogen in doped and undoped MgO crystals

Cited by 73 publications

References 31 publications

The influence of ferric iron and hydrogen on Fe–Mg interdiffusion in ferropericlase ((Mg,Fe)O) in the lower mantle

The influence of ferric iron and hydrogen on Fe–Mg interdiffusion in ferropericlase ((Mg,Fe)O) in the lower mantle

Dehydrogenation kinetics of pure and nickel-doped magnesium hydride investigated by in situ time-resolved powder X-ray diffraction

Nb-Gateway for Hydrogen Desorption in Nb₂O₅ Catalyzed MgH₂ Nanocomposite

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Diffusion of deuterium and hydrogen in doped and undoped MgO crystals

Cited by 73 publications

References 31 publications

The influence of ferric iron and hydrogen on Fe–Mg interdiffusion in ferropericlase ((Mg,Fe)O) in the lower mantle

The influence of ferric iron and hydrogen on Fe–Mg interdiffusion in ferropericlase ((Mg,Fe)O) in the lower mantle

Dehydrogenation kinetics of pure and nickel-doped magnesium hydride investigated by in situ time-resolved powder X-ray diffraction

Nb-Gateway for Hydrogen Desorption in Nb2O5 Catalyzed MgH2 Nanocomposite

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Nb-Gateway for Hydrogen Desorption in Nb₂O₅ Catalyzed MgH₂ Nanocomposite