Light-Metal Hydrides for Hydrogen Storage

Demands for zero greenhouse-gas emission vehicles have sharpened with today’s increased focus on global warming. Hydrogen storage is a key technology for the implementation of hydrogen powered vehicles. Metal hydrides can claim higher energy densities than alternative hydrogen storage materials, but a remaining challenge is to find a metal hydride which satisfies all current demands on practical usability. Several metals store large amounts of hydrogen by forming a metal hydride, e.g., Mg, Ti and Al. The main problems are the weight of the material and the reaction energy between the metal and hydrogen.
Magnesium has a high storage capacity (7.6 wt.% hydrogen) in forming MgH2; this is a slow reaction, but can be accelerated either by minimizing the diffusion length within the hydride or by changing the diffusion properties. Light-metal hydrides have been studied in this thesis with the goal of finding new hydrogen storage compounds and of gaining a better understanding of the parameters which determine their storage properties. Various magnesium-containing compounds have been investigated. These systems represent different ways to address the problems which arise in exploiting magnesium based materials. The compounds were synthesized in sealed tantalum tubes, and investigated by in situ synchrotron radiation X-ray powder diffraction, neutron powder diffraction, isothermal measurements, thermal desorption spectroscopy and electron microscopy.It is demonstrated that hydrogen storage properties can be improved by alloying magnesium with yttrium or scandium…


1. Introduction
2. The scope of this thesis
3. Metal hydrides as hydrogen storage materials
3.1 Complexes
3.2 Alloys
3.2.1 Alloys with yttrium and magnesium
3.2.2 Alloys with scandium and magnesium
4. Experimenta
4.1 Material synthesis
4.2 Hydrogen absorption
4.2.1 High pressure synthesis
4.2.2 Deuterium absorption
4.3 Diffraction
4.3.1 X-ray powder and single crystal diffraction
4.3.2 Synchrotron radiation X-ray powder diffraction
4.3.3 Neutron powder diffraction
4.3.4 Crystal structure determination and refinement
4.4 Absorption / desorption isotherms and thermal desorption spectroscopy
4.5 Microstructural analysis
4.6 Thermal analysis
4.7 Density functional theory calculations
5 Y-Mg-based alloys
5.1 Mg24Y5
5.1.1 Mg24Y5-Ti
5.2 YMgGa
5.3 Mg3Y2Zn3
5.4 Summary of the Y-Mg-based alloys
6 Sc-Mg-based alloys
6.1 Sc2MgGa2
6.2 Sc(Al1-xMgx), x  0.2
6.2.1 ScAl0.8Mg0.
6.2.2 Sc(Al1-xMgx), x  0.20
6.3 Summary of the Sc-Mg-based alloys
7. Concluding remarks
7.1 Parameters influencing hydrogen storage properties
7.2 Synthesis of new materials
Summary in Swedish

Author: Sahlberg, Martin

Source: Uppsala University Library

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