Hydrogen diffusion in Mg–H and Mg–Ni–H alloys

Čermák, Jan; Král, Lubomír

doi:10.1016/j.actamat.2008.02.003

Cited by 117 publications

(23 citation statements)

References 34 publications

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“…11,12 The formation of a 'blocking' layer of MgH 2 has been described previously in the literature and hence the diffusion length scale for complete reaction needs to be kept below 30-50 mm. The nucleation occurs at Pd-Mg (or the catalyst/additive-Mg interface) followed by growth due to the diffusion of H atoms to the growth front.…”

Section: Introductionmentioning

confidence: 99%

Nanometer-scale hydrogen ‘portals’ for the control of magnesium hydride formation

Chung

Nivargi

Clemens

2015

Phys. Chem. Chem. Phys.

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Magnesium and Mg-based material systems are attractive candidates for hydrogen storage but limited by unsuitable thermodynamic and kinetic properties. In particular, the kinetics are too slow at room temperature and atmospheric pressure. To study the hydride formation kinetics in a controlled way, we have designed a unique 'nanoportal' structure of Pd nanoparticles deposited on epitaxial Mg thin films, through which the hydride will nucleate only under Pd nanoparticles. We propose a growth mechanism for the hydrogenation reaction in the nanoportal structure, which is supported by scanning electron microscopy (SEM) images of hydrogenated samples exhibiting consistent results. Interestingly, the grain boundaries of Mg films play an important role in hydride nucleation and growth processes. Kinetic modeling based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) formalism seems to agree with the two-dimensional nucleation and growth mechanism hypothesized and the overall reaction rate is limited by hydrogen flux through the interface between the Pd nanoparticle and the underlying Mg film. The fact that in our structure Mg can be transformed completely into MgH2 with only a small percentage of Pd nanoparticles offers possibilities for future on-board storage applications.

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Section: Introductionmentioning

confidence: 99%

Nanometer-scale hydrogen ‘portals’ for the control of magnesium hydride formation

Chung

Nivargi

Clemens

2015

Phys. Chem. Chem. Phys.

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“…The XRD pattern of the as‐synthesized HCVD product (Figure c) confirmed the co‐existence of the two Mg 2 NiH 4 low‐temperature (LT) modifications: the prevailing untwinned‐phase Mg 2 NiH 4 ‐LT1 and the microtwinned‐phase Mg 2 NiH 4 ‐LT2 (typical peak at 2θ = 23.7°). Moreover, the MgO phase was detected, and its diffraction peaks obtained in this work were very broad and weak, indicating a relatively small grain size or finite thickness.…”

mentioning

confidence: 68%

“…By comparison, little work has been devoted to the fabrication of nanoconfined Mg‐based intermetallic hydrides, such as Mg 2 NiH 4 . Most reported ternary metal hydrides have been synthesized via a two‐step procedure consisting of the synthesis of binary intermetallic compounds and subsequent hydrogenation . This procedure is used primarily because their direct preparation and characterization in a reasonably clean form is highly challenging given the large differences in physical properties of the metals, e.g., vapor pressure, melting point, and diffusion coefficient .…”

mentioning

confidence: 99%

“…From the FESEM images in Figure d and Figure S4a,b (Supporting Information), it is clearly shown that well‐monodispersed Mg 2 NiH 4 NPs were pinned on GS within the whole sample regardless of the selection of the field, exhibiting strong interaction with the substrate. Typically, the two Mg 2 NiH 4 LT phases coexist when the Mg 2 Ni intermetallic powder is hydrogenated above the LT–HT transition temperature of ≈237 °C; however, they are not easy to distinguish from each other by XRD, which makes studying their detailed structural characteristics at the nanoscale difficult. Herein, by using the special gas–solid technique, we confined the well‐dispersed hydrides, encapsulating them in 2D arrangements on a substrate within a range of 10–150 nm, enabling the Mg 2 NiH 4 single crystals in the two modifications to be directly evaluated.…”

mentioning

confidence: 99%

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Metal Hydride Nanoparticles with Ultrahigh Structural Stability and Hydrogen Storage Activity Derived from Microencapsulated Nanoconfinement

et al. 2017

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Metal hydrides (MHs) have recently been designed for hydrogen sensors, switchable mirrors, rechargeable batteries, and other energy-storage and conversion-related applications. The demands of MHs, particular fast hydrogen absorption/desorption kinetics, have brought their sizes to nanoscale. However, the nanostructured MHs generally suffer from surface passivation and low aggregation-resisting structural stability upon absorption/desorption. This study reports a novel strategy named microencapsulated nanoconfinement to realize local synthesis of nano-MHs, which possess ultrahigh structural stability and superior desorption kinetics. Monodispersed Mg NiH single crystal nanoparticles (NPs) are in situ encapsulated on the surface of graphene sheets (GS) through facile gas-solid reactions. This well-defined MgO coating layer with a thickness of ≈3 nm efficiently separates the NPs from each other to prevent aggregation during hydrogen absorption/desorption cycles, leading to excellent thermal and mechanical stability. More interestingly, the MgO layer shows superior gas-selective permeability to prevent further oxidation of Mg NiH meanwhile accessible for hydrogen absorption/desorption. As a result, an extremely low activation energy (31.2 kJ mol ) for the dehydrogenation reaction is achieved. This study provides alternative insights into designing nanosized MHs with both excellent hydrogen storage activity and thermal/mechanical stability exempting surface modification by agents.

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“…Our determination is well within the range of group 1) values, obtained from hydrogen absorption and desorption measurements. Moreover, the value from [21], the only one that corresponds to MgH 2 without additives, can be matched by setting g equal to 0.01. This g value implies that 1% of the surface is "activated" by milling in each milling event, a more realistic assumption than setting g equal to 1.…”

Section: 3mentioning

confidence: 99%

MgH2 synthesis during reactive mechanical alloying studied by in-situ pressure monitoring

Castro

Fuster

Urretavizcaya

2012

International Journal of Hydrogen Energy

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Hydrogen diffusion in Mg–H and Mg–Ni–H alloys

Cited by 117 publications

References 34 publications

Nanometer-scale hydrogen ‘portals’ for the control of magnesium hydride formation

Nanometer-scale hydrogen ‘portals’ for the control of magnesium hydride formation

Metal Hydride Nanoparticles with Ultrahigh Structural Stability and Hydrogen Storage Activity Derived from Microencapsulated Nanoconfinement

MgH2 synthesis during reactive mechanical alloying studied by in-situ pressure monitoring

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