Abstract
AbstractNanosized 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 MgH2 as a reference material for in-situ TEM experiments under low-dose conditions to study and quantitatively understand the electron beam-induced dehydrogenation. For this, valence electron energy loss spectroscopy (VEELS) measurements are conducted in a monochromated FEI Titan3 80–300 microscope. From observing the plasmonic absorptions it is found that MgH2 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 high-energy electrons by the MgH2 plasmon. The obtained insights are also relevant for the TEM characterization of other hydrides.
Highlights
Hydrogen is a promising clean energy carrier that has the potential of replacing fossil fuels in a future sustainable economy
It is not possible to acquire a transmission electron microscopy (TEM) bright field image of the ball-milled MgH2 in the hydrogenated phase with the CCD camera even at low magnifications, since the electron dose, that is needed for an acquisition with the CCD with a decent signal-to-noise ratio, already causes massive dehydrogenation
The red, 36 × 36 nm2 large square in Fig. 1 depicts the area of the specimens, from where the VEEL spectra are acquired with the CCD camera of the energy filter system under low-dose conditions
Summary
Hydrogen is a promising clean energy carrier that has the potential of replacing fossil fuels in a future sustainable economy. Hydrogen storage in a safe and efficient way remains a challenge. MgH2, is a promising and well-studied material, because of its high reversible hydrogen storage capacity of 7.6 wt% and its low cost. The unfavorable high thermodynamic stability and poor reaction kinetics still limit the application of MgH2 for hydrogen storage today. High-energy ball milling has been widely used to prepare nanostructured Mg(H2) based materials with grain sizes in the nanometer regime, which resulted in significantly improved kinetics [1, 3,4,5,6,7,8]. The stabilization of small grain sizes upon cycling and potential
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