Extremely Pure Mg2FeH6 as a Negative Electrode for Lithium Batteries

First-principles calculations of Mg2FeH6 under high pressures and hydrogen storage properties

We report on structural properties, elastic constants, mechanical and dynamical stabilities, electronic band structure, and hydrogen storage applications of Mg2FeH6 at zero and high-pressure effects. The work has been realized within the full-potential linearized augmented plane wave method. At zero pressure, the material under study is stable and has a ductile nature. The electronic structure of the material of interest is determined to be X-X wide direct band gap semiconductor with an energy of 1.88 eV. The hydrogen storage capacity wt (%) and the hydrogen desorption temperature are reported as 5.473 and 625.47 K respectively. The Debye temperature ϴD is recorded as 698 K using the elastic constants and about 775 K using the Gibbs calculations. Under high-pressure effect up to 80 GPa, the semiconductor still be an X-X semiconductor with an energy gap of 3.91 eV. The Debye temperature ϴD increases monotonically up to about 1120 K at 80 GPa when using the calculated elastic constants whereas the desorption temperature decreases from 650 to 0 K by increasing pressure from 0 to about 87 GPa.

Promising Isotope Effect in Pd77Ag23 for Hydrogen Separation

Pd–Ag alloys are largely used as hydrogen separation membranes and, as a consequence, the Pd–Ag–H system has been intensively studied. On the contrary, fewer information is available for the Pd–Ag–D system; thus, the aim of this work is to improve the knowledge of the isotope effect on the commercial Pd77Ag23 alloy, especially for temperature above 200 °C. In particular, deuterium absorption measurements are carried out in the Pd77Ag23 alloy in the temperature range between 79 and 400 °C and in the pressure range between 10−2 and 16 bar. In this exploited pressure (p) and composition (c) range, above 300 °C the pc isotherms display the typical shape of materials where only a solid solution of deuterium is present while at lower temperatures these curves seem to be better described by the coexistence of a solid solution and a deuteride in a large composition range. The obtained results are compared and discussed with the ones previously measured with the lightest hydrogen isotope. Such a comparison shows that the Pd77Ag23 alloy exhibits a clear inverse isotope effect, as the equilibrium pressure of the Pd–Ag–D system is higher than in Pd–Ag–H by a factor of ≈2 and the solubility of deuterium is about one half of that of hydrogen. In addition, the absorption measurements were used to assess the deuteration enthalpy that below 300 °C is ΔHdeut = 31.9 ± 0.3 kJ/mol, while for temperatures higher than 300 °C, ΔHdeut increases to 43 ± 1 kJ/mol. Additionally, in this case a comparison with the lighter isotope is given and both deuteration enthalpy values result lower than those reported for hydrogenation. The results described in this paper are of practical interest for applications operating above 200 °C, such as membranes or packing column, in which Pd77Ag23 has to interact with a gas stream containing both hydrogen isotopes.

Magnesium-Based Materials for Hydrogen Storage-A Scope Review

Magnesium hydride and selected magnesium-based ternary hydride (Mg2FeH6, Mg2NiH4, and Mg2CoH5) syntheses and modification methods, as well as the properties of the obtained materials, which are modified mostly by mechanical synthesis or milling, are reviewed in this work. The roles of selected additives (oxides, halides, and intermetallics), nanostructurization, polymorphic transformations, and cyclic stability are described. Despite the many years of investigations related to these hydrides and the significant number of different additives used, there are still many unknown factors that affect their hydrogen storage properties, reaction yield, and stability. The described compounds seem to be extremely interesting from a theoretical point of view. However, their practical application still remains debatable.