New Insight on the Hydrogen Absorption Evolution of the Mg–Fe–H System under Equilibrium Conditions

Abstract

Mg2FeH6 is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m3) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg2FeH6 under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg2FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH2 is enhanced by the presence of Fe. However, MgH2 does not take part as intermediate for the formation of Mg2FeH6 and acts as solid-solid diffusion barrier which hinders the complete formation of Mg2FeH6. This work provides novel insight about the formation mechanism of Mg2FeH6.

Review on Hydrogen Storage Performance of MgH2: Development and Trends

“…J. Puszkiel et al [92] . confirm that the formation mechanism of Mg 2 FeH 6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds.…”

Magnesium-Based Materials for Hydrogen Storage—A Scope Review

“…The formation mechanism of complex hydrides of Mg 2 FeH 6 under equilibrium conditions has been broadly investigated recently [ 38 , 209 , 210 , 224 , 225 ]. In most cases, hydride synthesis results in a MgH 2 -Mg 2 FeH 6 hydride mixture [ 35 , 36 , 37 , 38 , 204 , 226 ].…”

“…Puszkiel et al [ 224 ] proposed a mechanism of Mg 2 FeH 6 formation under equilibrium conditions for a 2MgH 2 -Fe powder mixture. During BM of the mixture, Mg 2 FeH 6 and MgH 2 were found to exist together from the beginning, but Mg 2 FeH 6 was a result of reactions between elemental Fe and Mg.…”

Improved kinetic behaviour of Mg(NH2)2-2LiH doped with nanostructured K-modified-LixTiyOz for hydrogen storage

“…All samples were prepared into a glove box with controlled O 2 and H 2 O atmosphere (<1 ppm) by dispersing the powders onto carbon grids. In order to avoid the oxidation/hydrolysis of the material at the time to introduce the grids into the microscope column, the dispersed powder on the grid was covered with a special polymeric film which does not preclude the electron interactions with the sample 57 . Then, HR-TEM observations of the identified Fe zones were done.…”