Crystalline structure, energy calculation and dehydriding thermodynamics of magnesium hydride from reactive milling

Zhou, Shixue; Zhang, Qianqian; Chen, Haipeng; Zang, Xuejing; Zhou, Xinpei; Wang, Ruolin; Jiang, Xiaojing; Ye, Bo; Jiang, Ruiqian

doi:10.1016/j.ijhydene.2015.02.059

Cited by 20 publications

(14 citation statements)

References 27 publications

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“…They concluded that formation of γ-MgH 2 crystallites, which is predominantly observed in the smaller powder particles, is an important contributor to the lowering of dehydrogenation temperatures in ball-milled MgH 2 . The recent differential scanning calorimetric studies of Zhou et al confirm that γ-MgH 2 exhibits a much lower hydrogen desorption temperature than α-MgH 2 (termed β-MgH 2 in their study) [5].…”

Section: Introductionmentioning

confidence: 66%

Point-defect kinetics in α- and γ-MgH2

Sander

Ismer

Walle

2016

International Journal of Hydrogen Energy

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The kinetics of hydrogen desorption from storage materials in principle depend on the crystalline phase of the material. In MgH 2 , desorption rates may be higher in the crystalline γ phase compared to the equilibrium bulk α phase. It has been suggested [R. A. Varin, T. Czujko, Z. Wronski, Nanotechnol., 17 (15) (2006) 3856-3865] that this effect is responsible for enhanced desorption from ball-milled MgH 2 , since smaller particles contain a higher proportion of the metastable γ phase. We investigate hydrogen transport kinetics in these phases of MgH 2 by using first-principles calculations based on density functional theory. Imposing charge neutrality, we find that the formation energy of hydrogen vacancies in γ-MgH 2 is smaller by 0.032 eV compared to α-MgH 2. Our calculations of migration barriers show that the only relevant point defect for mass transport in both crystal structures is the positively charged hydrogen vacancy, and that its lowest migration barrier in γ-MgH 2 is 0.02 eV lower than in α-MgH 2. We conclude that hydrogen vacancies exist in higher concentrations and are also more mobile in the γ phase than in the α phase, thus explaining the faster dehydrogenation kinetics of γ-MgH 2 .

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Section: Introductionmentioning

confidence: 66%

Point-defect kinetics in α- and γ-MgH2

Sander

Ismer

Walle

2016

International Journal of Hydrogen Energy

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“…When the Mg-Pd nanocomposite was hydrogenated under 3 MPa hydrogen pressure at 150 • C for 2 h, the majority phases of the hydrogenated Mg-Pd nanocomposite are the tetragonal β-MgH 2 and the orthogonal γ-MgH 2 , along with a small amount of MgO and PdH 0.706 phases, as shown in Figure 1B. The metastable γ-MgH 2 , belonging to a-PbO 2 -type orthorhombic crystal structure, is usually produced by ball milling (Varin et al, 2006;Ponthieu et al, 2013;Zhou et al, 2015) as well as under high compressive stress (Vajeeston et al, 2006;Siviero et al, 2009;Ham et al, 2013). Zhou et al (2013) pointed out that the H octahedrons surrounding Mg atoms are deformed in the γ-MgH 2 .…”

Section: Sample Characterizationmentioning

confidence: 99%

“…The γ-MgH 2 phase is known to be less stable than the β-MgH 2 phase. The plane (110) of γ-MgH 2 has a predicted enthalpy of 44.66 kJ mol −1 H 2 , while for the same β-MgH 2 plane, the enthalpy is 78.16 kJ mol −1 H 2 (Zhou et al, 2015). In addition, the heavily distorted MgH 6 octahedron in the γ-MgH 2 potentially can facilitate hydrogen diffusion (Sander et al, 2016).…”

Section: Microstructural Characterizationmentioning

confidence: 99%

Magnesium Nanoparticles With Pd Decoration for Hydrogen Storage

et al. 2020

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In this work, Magnesium nanoparticles with Pd decoration, ranging from 40 to 70 nm, were successfully coprecipitated from tetrahydrofuran (THF) solution, assigned as the Mg-Pd nanocomposite. The Mg-Pd nanocomposite exhibits superior hydrogen storage properties. For the hydrogenated Mg-Pd nanocomposite at 150 • C, the onset dehydrogenation temperature is significantly reduced to 216.8 • C, with a lower apparent activation energy for dehydrogenation of 93.8 kJ/mol H 2 . High-content γ-MgH 2 formed during the hydrogenation process, along with PH 0.706 , contributes to the enhancing of desorption kinetics. The Mg-Pd nanocomposite can take up 3.0 wt% hydrogen in 2 h at a temperature as low as 50 • C. During lower hydrogenation temperatures, Pd can dissociate hydrogen and create a hydrogen diffusion pathway for the Mg nanoparticles, leading to the decrease of the hydrogenation apparent activation energy (44.3 kJ/mol H 2 ). In addition, the Mg-Pd alloy formed during the hydrogenation/dehydrogenation process can play an active role in the reversible metal hydride transformation, destabilizing the MgH 2 .

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“…However, there is an urgent need to address the agglomeration of particles in support-free nano-scaled hydrides or nanowires since it results in collapse of the nanostructure aer repeated hydrogen uptake and release cycles, which is still a signicant challenge. It is generally accepted that nano-connement leads to an obvious loss in the gravimetric 12 prepared magnesium hydride via reactive milling under a hydrogen atmosphere using carbon as a milling aid. The enthalpy change determined by experimental isotherms gradually decreased with more g-MgH 2 from a longer milling time.…”

Section: Nanoconnementmentioning

confidence: 99%

“…Besides, the synthesis of nanostructured materials is another challenge for practical applications.À2 and enthalpy change of 78.16 kJ mol À1 . This is because in g-MgH 2 , the H octahedrons surrounding the Mg atoms are deformed and the octahedron chain takes a zigzag form instead of the straight chain in the b phase 12. Thus, we can conclude that conversion to the metastable g-MgH 2 phase should lead to improved hydrogen sorption properties and provide another approach to modify the thermodynamics of Mg-based materials.…”

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confidence: 94%