MgH<sub>2</sub>→ Mg phase transformation driven by a high-energy electron beam: An<i>in situ</i>transmission electron microscopy study

Paik, Biswajit; Jones, I.P.; Walton, Allan; Mann, Vicky; Book, D. L.; Harris, I.R.

doi:10.1080/09500830903272892

Cited by 32 publications

(24 citation statements)

References 15 publications

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“…This considerably hinders studying the hydride phase with high spatial resolution, unless a cryogenically cooled liquid nitrogen sample holder is used, which again limits the spatial resolution. The electron-beam-induced dehydrogenation was monitored in-situ by electron diffraction to identify the crystallographic orientation relation between MgH 2 and Mg [21,22]. This dehydrogenation was further observed in-situ by valence electron energy loss spectroscopy (VEELS) [8,12,21], where both phases can be identified by their distinct plasmon energies [23].…”

Section: Introductionmentioning

confidence: 99%

“…The electron-beam-induced dehydrogenation was monitored in-situ by electron diffraction to identify the crystallographic orientation relation between MgH 2 and Mg [21,22]. This dehydrogenation was further observed in-situ by valence electron energy loss spectroscopy (VEELS) [8,12,21], where both phases can be identified by their distinct plasmon energies [23]. However, little is known about the mechanism governing the rate of the electron-beam-induced dehydrogenation and a quantitative description of this effect is lacking.…”

Section: Introductionmentioning

confidence: 99%

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Electron beam induced dehydrogenation of MgH2 studied by VEELS

Surrey

Schultz

Rellinghaus

2016

Adv Struct Chem Imag

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Nanosized or nanoconfined hydrides are promising materials for solid-state hydrogen storage. Most of these hydrides, however, degrade fast during the structural characterization utilizing transmission electron microscopy (TEM) upon the irradiation with the imaging electron beam due to radiolysis. We use ball-milled MgH 2 as a reference material for in-situ TEM experiments under low-dose conditions to study and quantitatively understand the electron beaminduced dehydrogenation. For this, valence electron energy loss spectroscopy (VEELS) measurements are conducted in a monochromated FEI Titan 3 80-300 microscope. From observing the plasmonic absorptions it is found that MgH 2 successively converts into Mg upon electron irradiation. The temporal evolution of the spectra is analyzed quantitatively to determine the thickness-dependent, characteristic electron doses for electron energies of both 80 and 300 keV. The measured electron doses can be quantitatively explained by the inelastic scattering of the incident highenergy electrons by the MgH 2 plasmon. The obtained insights are also relevant for the TEM characterization of other hydrides.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electron beam induced dehydrogenation of MgH2 studied by VEELS

Surrey

Schultz

Rellinghaus

2016

Adv Struct Chem Imag

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“…It is well known that MgH 2 decomposes to Mg in the TEM within seconds due to radiolysis1234567. This effect is largely underestimated by Nogita et al 8.…”

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confidence: 99%

Comments on ”Evidence of the hydrogen release mechanism in bulk MgH2”

Surrey

Nielsch

Rellinghaus

2017

Sci Rep

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The effect of an electron beam induced dehydrogenation of MgH2 in the transmission electron microscope (TEM) is largely underestimated by Nogita et al., and led the authors to a misinterpretation of their TEM observations. Firstly, the selected area diffraction (SAD) pattern is falsely interpreted. A re-evaluation of the SAD pattern reveals that no MgH2 is present in the sample, but that it rather consists of Mg and MgO only. Secondly, the transformation of the sample upon in-situ heating in the TEM cannot be ascribed to dehydrogenation, but is rather to be explained by the (nanoscale) Kirkendall effect, which leads to the formation of hollow MgO shells without any metallic Mg in their cores. Hence, the conclusions drawn from the TEM investigation are invalid, as the authors apparently have never studied MgH2.

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“…As such, in-situ temperature controlled TEM observation is an attractive approach for determining the mechanism of hydrogen release. Three groups have reported using in-situ TEM at 200 kV to observe hydrogen desorption 15 17 18 . However, conventional TEM with an accelerating voltage of 200 kV has disadvantages including inelastic incident beam interactions with the samples, and the sample dimensions (typically less than 100 nm in thickness) make surface effects more prominent 19 .…”

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confidence: 99%

Evidence of the hydrogen release mechanism in bulk MgH2

Nogita

Tran

Yamamoto

et al. 2015

Sci Rep

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Hydrogen has the potential to power much of the modern world with only water as a by-product, but storing hydrogen safely and efficiently in solid form such as magnesium hydride remains a major obstacle. A significant challenge has been the difficulty of proving the hydriding/dehydriding mechanisms and, therefore, the mechanisms have long been the subject of debate. Here we use in situ ultra-high voltage transmission electron microscopy (TEM) to directly verify the mechanisms of the hydride decomposition of bulk MgH2 in Mg-Ni alloys. We find that the hydrogen release mechanism from bulk (2 μm) MgH2 particles is based on the growth of multiple pre-existing Mg crystallites within the MgH2 matrix, present due to the difficulty of fully transforming all Mg during a hydrogenation cycle whereas, in thin samples analogous to nano-powders, dehydriding occurs by a ‘shrinking core' mechanism.

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MgH₂→ Mg phase transformation driven by a high-energy electron beam: Anin situtransmission electron microscopy study

Cited by 32 publications

References 15 publications

Electron beam induced dehydrogenation of MgH2 studied by VEELS

Electron beam induced dehydrogenation of MgH2 studied by VEELS

Comments on ”Evidence of the hydrogen release mechanism in bulk MgH2”

Evidence of the hydrogen release mechanism in bulk MgH2

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MgH2→ Mg phase transformation driven by a high-energy electron beam: Anin situtransmission electron microscopy study

Cited by 32 publications

References 15 publications

Electron beam induced dehydrogenation of MgH2 studied by VEELS

Electron beam induced dehydrogenation of MgH2 studied by VEELS

Comments on ”Evidence of the hydrogen release mechanism in bulk MgH2”

Evidence of the hydrogen release mechanism in bulk MgH2

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MgH₂→ Mg phase transformation driven by a high-energy electron beam: Anin situtransmission electron microscopy study