SusChEM: Structural and Mechanistic Insights into the Enhanced Hydrogen Sorption Properties of Metal Hydride Nanoparticles Made via Solution Reactions

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Hydrogen is an ideal fuel for vehicles and other portable applications because it burns cleanly in air and the only byproduct is water. It also has a very high energy density, almost three times higher than gasoline. The main challenges to using hydrogen as a fuel, however, are its clean production and storage. Storing hydrogen as a gas requires large cylinders, and storing it as a liquid requires high pressures and very low temperatures. Both methods also present safety challenges. Dr. Prieto is exploring the use of solid compounds as storage materials for hydrogen. This approach offers small storage volumes at reasonable pressures. Light metal hydrides, such as magnesium metal, can store a lot of hydrogen per unit mass, but the drawbacks are that putting the hydrogen into magnesium requires high temperatures and pressures, and removing the hydrogen requires high temperatures and low pressures. Both processes are very slow. Dr. Prieto and her students have designed a method of making very small particles of magnesium that display much faster rates for storing hydrogen. The goal of her work is to determine whether the addition of small amounts of other metals to the surface of the magnesium can further increase the rates of adding or removing the hydrogen from the metal particles. She uses techniques such as X-ray diffraction, thermal analysis, solid state nuclear magnetic resonance, and X-ray absorption experiments to help model the rates of the hydrogenation reactions and to provide data that aid in developing kinetic models to describe these reactions. Dr. Prieto involves students ranging from high school to graduate levels in her research, and the practical applications of this work serve as a useful recruiting tool to attract talented students and train them in research aimed at improving energy sustainability. Prof. Prieto communicates her knowledge of hydrogen storage and energy sustainability to the general public through her role as a board member of the Colorado Clean Energy Cluster, which is directly impacting policy in Colorado for economic development and projects related to clean energy production, storage, and transportation. This project is used as an example of basic research that can be easily linked to an application interesting to a wide audience, that of clean energy production and storage. Hydrogen is an ideal fuel for portable applications because it burns cleanly in air to produce water, and it has a very high energy density. Magnesium (Mg), doped Mg, and Mg alloys are promising materials for hydrogen storage due to their high theoretical hydrogen storage capacities (e.g. 7.6 weight% for MgH2). However, bulk Mg is less than ideal as a hydrogen storage material due to the slow kinetics and high temperatures required for hydrogen absorption and desorption. Dr. Prieto is synthesizing nanoparticles of hydrogen storage materials in which the reduced size results in significantly enhanced kinetics for hydrogen storage. She is determining the relative roles of kinetics and thermodynamics on the hydrogen sorption and desorption of these particles, particularly upon addition of small amounts of transition metals to the surface. Although faster hydrogenation rates have been observed for nanoscale metal hydrides, very little is known about the roles of increased surface area versus impurities and defects. The targets Dr. Prieto is studying are earth abundant elements that are light and store large amounts of hydrogen, albeit sluggishly in the bulk. With control over the particle size and additive type and position, she can dramatically increase the slow hydrogenation rates observed in the bulk and, ultimately, be able to lower the temperature required for hydrogenation of these materials. This research results in recruiting and retaining a talented, diverse group of students.