Hydrogen storage properties of magnesium based nanostructured materials produced by glancing angle deposition

Hydrogen is proposed as an ideal fuel for future global energy requirements with the potential to reduce carbon dioxide and other greenhouse gas emissions and improve energy independence for countries. Hydrogen is ideal for mobile applications, such as transportation vehicles and mobile devices. However storage of hydrogen remains as a challenge to realize this transition.;One of the promising approaches in solid state storage is storing hydrogen in the form of metal hydrides. High hydrogen storage capacity of 7.6 wt% (weight percentage), reversibility, low cost, and abundance make magnesium an attractive material for solid state hydrogen storage.;The main drawbacks of MgH2 as a hydrogen carrier are the high temperature of reaction, slow desorption kinetics and high reactivity with oxygen. Most of the research for improvement of storage characteristics used catalysts and alloying techniques. However, they failed to provide kinetic and thermodynamic enhancements to meet the US Department of Energy (DOE) requirements.;Nanostructured Mg have been shown to provide faster kinetics and improved thermodynamic properties benefiting from increased surface area of interaction and decreased diffusion lengths of hydrogen into/out-of material. However, techniques such as ball-milling, vapor transport, thin film deposition still are in lack of providing the targeted improvements.;The goal of this study is to investigate oxidation properties, structure, morphology and hydrogen storage properties of magnesium nanostructures fabricated by glancing angle deposition (GLAD) technique using characterization techniques including as SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), XRD (X-Ray Diffraction), TGA (Thermo Gravimetric Analysis) and QCM (Quartz Crystal Microbalance).;A new quartz crystal microbalance (QCM) hydrogen storage testing system has been developed. Hydrogen storage behaviors of magnesium nanostructures under constant and variable temperature regimes were studied. Activation energies for absorption and desorption were calculated. The studies show that GLAD Mg nanorods have single crystal structure and enhanced oxidation resistance compared to thin film counterparts. GLAD structures also exhibit crystal orientations different than thin films which favor hydrogen diffusion into the structure. Mg nanotrees deposited by thermal evaporation GLAD show enhanced storage characteristics. Additionally, using a variable temperature process for storage significantly improves hydrogen storage absorption rates and capacities.