Intellectual Merits: Hydrogen storage is the bottleneck for using hydrogen energy in on-board vehicle applications. In the pursuit of metal hydrides as solid state hydrogen storage media, magnesium hydride is considered to be a good candidate because of its lightweight, low cost, and high theoretical hydrogen storage capacity of 7.6 wt.%. Unfortunately, its high thermodynamic stability and sluggish reaction kinetics limit its practical applications. By tailoring the structural properties of nanomaterials, the thermodynamics and kinetics of hydrogen adsorption can be designed to satisfy the future hydrogen storage requirements. A fundamental understanding of hydrogen-nanostructure interactions also depends largely on the ability to fabricate nanostructures with the desired structural properties. In this proposal, the main goal is to use a novel nanofabrication technique, glancing angle deposition (GLAD), to design and produce novel Mg-catalyst nano-architectures with different topography, structure, and composition. This fabrication technique provides one with a vehicle to investigate the following important questions for hydrogen storage applications: (1) How would different nanoscale structures change the hydrogen storage behavior? (2) Would nanoscale catalysts, incorporated into nanostructured hydrogen storage materials in different forms, greatly enhance the storage behavior? Using this nanofabrication technique, the PI proposes to fabricate metal hydride nanostructures with different topographic structures to investigate the hydrogen storage ability and sorption performance. The hydrogen sorption performances of the nanostructures will be further improved by depositing different catalysts with different sizes and geometric forms. Broader Impacts: The success of this project will generate the following benefits: (1) It provides a generic methodology to fabricate well-designed metal hydride nanostructures or multilayered nanostructures. Therefore, the metal hydride materials that can be tailored into nanostructures are not limited to the proposed materials. (2) With the systematically designed metal hydride nanostructures and advanced characterization techniques, one can study at a fundamental level how hydrogen interacts with well-defined metal hydride nanostructures. (3) Optimal structures and conditions for fabricating the best metal hydride nanostructures for highly efficient hydrogen storage could be found. The lab-based nanotechnology course module that the PI will create will allow undergraduate and high school students to obtain provide hands-on experience on nanofabrication.
Hydrogen storage is the bottleneck for using hydrogen energy in on-board vehicle applications. In the pursuit of metal hydrides as solid state hydrogen storage media, magnesium hydride is considered to be a good candidate because of its lightweight, low cost, and high theoretical hydrogen storage capacity of 7.6 wt.% in MgH2. Unfortunately, its high thermodynamic stability and sluggish reaction kinetics limit its practical applications. By tailoring the structural properties of nanomaterials, the thermodynamics and kinetics of hydrogen adsorption can be designed to satisfy the future hydrogen storage requirements. A fundamental understanding of hydrogen-nanostructure interactions also depends largely on the ability to fabricate nanostructures with the desired structural properties. In this project, our main goal is to use a novel nanofabrication technique, glancing angle deposition, to design and produce novel Mg-catalyst nano-architectures with different topography, structure, and composition. This fabrication technique provides us with a vehicle to investigate the following important questions regarding hydrogen storage applications: (1) How would different nanoscale structures change the hydrogen storage behavior? (2) Would nanoscale catalysts, incorporated into nanostructured hydrogen storage materials in different forms, greatly enhance the storage behavior? During the 1.5 year NSF project period, we have successfully fabricated the V decorated and doped Mg nanostructures as proposed. We have used multiple characterization techniques to investigate the hydrogenation performance of those nanostructures. We found that for both structures the hydrogenation temperature became significantly lower than that of the pure Mg nanostructures. The hydrogen uptake temperature can lower to about 170oC, and hydrogen release temperature becomes 210oC, compared to about 350oC for pure Mg. The V-doped Mg nanostructures give a better thermodynamic and kinetic performance compared to those for the V-decorated Mg nanostructures. The results demonstrate that different nanostructures can modulate the hydrogenation performance of Mg, which shows great promise to further engineer this material into practical applications. However, the fundamental reason why such a difference occurs is still not very clear. In addition, we have also used a unique two-source electron beam evaporation system to fabricate the Al, B, Ni, Ti and V doped Mg nanostructures. We found that the composition and amount of the dopant played an important role in the morphology of the fabricated Mg nanostructures, and also significantly affected the crystal structures of the doped samples. The hydrogenation performance shows that the Ni, Ti, and V doped Mg nanostructures gave better hydrogenation absorption and desorption behaviors. We are still investigating how different dopants affect the hydrogenation performance. From the results of this project, we conclude that (1) the glancing angle deposition provides a generic methodology to fabricate well-designed metal hydride nanostructures or multilayered nanostructures. Therefore, the metal hydride materials that can be tailored into nanostructures are not limited to the proposed materials. (2) With the systematically designed metal hydride nanostructures and advanced characterization techniques, we can understand at a fundamental level how hydrogen interacts with well-defined metal hydride nanostructures. (3) With further understanding, we can find the optimum structures and conditions for fabricating the best metal hydride nanostructures for highly efficient hydrogen storage. This project has trained one postdoctoral research associate, and involved three undergraduate students and a summer high school students. Results from the project have been used in the PI’s physics lecture regarding clean energy. It has produced 4 peer reviewed journal publications, 4 manuscripts that are under review or in preparation, and 4 conference talks.
