Aline Léon

Synthesis and properties of magnesium tetrahydroborate, Mg(BH4)2

Mg(BH4)2 is one of the few complex hydrides which have the potential to meet the requirements for hydrogen storage materials, because it contains 14.9 mass% H and has suitable thermodynamic properties. It has not been investigated for hydrogen storage applications yet. In this study, several ways to synthesize solvated and desolvated magnesium tetrahydroborate by wet chemical and mechanochemical methods were tested and compared. A direct synthesis by a reaction of MgH2 with aminoboranes yields magnesium tetrahydroborate quantitatively and in pure form. The method is also applicable to the synthesis of other tetrahydroborates. The products were characterized by elemental analysis, in situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermal analysis methods, such as thermogravimetric analysis (TGA-DSC) and high-pressure calorimetry under a hydrogen atmosphere (HP-DSC).

Hydrogenation characteristics of air-exposed magnesium films

Abstract A study of the hydrogenation characteristics of 30-μm thick air-exposed magnesium film has been made using a volumetric method. Magnesium films were prepared by vacuum evaporation. Morphological and structural properties were studied by scanning electron microscopy, X-ray diffraction and Auger profile. It was shown that magnesium films absorb hydrogen at 623 K under 10 bar of hydrogen pressure and desorb it at the same temperature under a residual hydrogen pressure of 0.21 bar. The first absorption follows a nucleation and growth process. Furthermore, macroscopic and microscopic observations made at different stages of the absorption–desorption process are presented.

Hydrogen sorption properties of vanadium- and palladium-implanted magnesium films

Abstract Magnesium films prepared by vacuum evaporation were implanted with vanadium and palladium ions in order to study their hydrogenation characteristics. It was found that the hydrogenation kinetics depend on the ion species and on the ion dose implanted. Indeed, the vanadium-implanted magnesium films have faster kinetics than the palladium-implanted ones. However, low vanadium concentration (∼0.3 at.%) seems to inhibit the absorption reaction. Among the ion-implanted magnesium films, the fastest kinetics were obtained with the vanadium-implanted film at a dose of 1×1016 ions/cm2: at 623 K and under a hydrogen pressure of 10 bar, a concentration of 6 wt.% of hydrogen was reached in 270 min during the first hydrogenation and in 45 min during the second one.

Magnesium Films for Hydrogen Storage

Metal hydrides are one of the most promising systems for safe hydrogen storage. Among these, magnesium hydride is particularly attractive because of its high hydrogen storage capacity and low cost. Unfortunately, pure magnesium has poor hydrogenation characteristics : slow hydrogen sorption kinetics and high temperature of operation. New materials such as nanocrystalline alloys, materials prepared by plasma techniques and evaporation-condensation have been studied elsewhere in order to circumvent these disadvantages. In the present work, we studied pure magnesium films prepared by vacuum evaporation. The structural and hydrogen sorption properties of magnesium film are presented. Morphology and structural properties were studied by scanning electron microscopy (SEM), X-Ray Diffraction (XRD) and Rutherford Backscattering Spectrometry (RBS). Hydrogen sorption properties were studied using pressure-composition isotherm measurements. Pure magnesium films were found to have better hydrogen sorption kinetics compared to magnesium hydride powder although the temperature of operation is still high.

X-ray Absorption Fine Structure (XAFS) Spectroscopy

17d.1 X-ray Absorption Fine Structure (XAFS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605 17d.1.1 Experimental Setup and Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 606 17d.1.2 EXAFS: Extended X-ray Absorption Fine Structure . . . . . . . . . . . . . . . . . . 608 17d.1.3 XANES: X-ray Absorption Near-Edge Structure . . . . . . . . . . . . . . . . . . . . . 611 17d.2 Investigation of Ti-doped NaAlH4 by XAFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612 17d.2.1 Initial Dehydrogenation/Rehydrogenation with TiCl3 as Dopant Material . 613 17d.2.2 Ti13 · 6THF in Comparison to TiCl3 as Dopant Material – Further Hydrogen Cycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616 17d.2.3 An Alternative Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619 17d.3 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621

Magnesium film implanted with vanadium ions for hydrogen storage

Preliminary results on the hydrogenation characteristics of vanadium-implanted magnesium films are presented. Magnesium films were prepared by vacuum evaporation. Some of them were then implanted with vanadium in order to improve their kinetics and lower the temperature of operation. The structural and hydrogen sorption properties of pure magnesium as well as ion-implanted magnesium films are described. The effects of vanadium ion implantation on hydrogen diffusion will be discussed.