Fall 2003 MRS Hydrogen Storage Tutorial notes:
mrs.org
Hydrogen Storage Materials: Science and Technology
To have an economy fueled by hydrogen, a supply of hydrogen is needed, a supply that can be stored, transported, and accessed safely and inexpensively. This tutorial, part of symposium BB, looked at methods of hydrogen storage as a necessary part of that infrastructure. Gholam-Abbas Nazri (General Motors R&D Center) began with an overview of fundamentals of hydrogen storage, introducing complex chemical hydrides, carbonaceous materials, and composites. While hydrogen can be stored as a compressed gas or in liquid form, these methods do not have a high enough energy density (along with other issues), and long-term solutions are built on solids. Here is where materials breakthroughs are still needed.
As emphasized by Rosa Young (Chevron Texaco Ovonic) in the second part of the tutorial, it is not enough to trap large quantities of hydrogen in a solid; the hydrogen also has to be easily released, reversibly. Storage can be accomplished through chemical bonding (e.g., hydrides) or through physical bonding (e.g., held inside carbon nanotubes). Metal hydrides (metallic bonding) hold promise over chemical hydrides (ionic and/or covalent bonding) because the hydrogen is stored interstitially and has no structure change, so is more likely to be reversible at a reasonable temperature. One area of focus is on hydrides with an AB, AB2, AB5, or a bcc structure. The challenge is to improve the weight percent of hydrogen that the solid can hold. Young gave details of the chemistry, structure, and thermodynamics of various hydrides and described a demonstration model of a Toyota Prius retrofitted with a metal hydride fuel storage system. In the final section of the tutorial, Ping Chen (National University of Singapore) looked further into the future, focusing on nitrides in the Li-N-H and Ca-N-H systems for hydrogen storage. Such materials show high storage capacity and fast kinetics (e.g. for "refueling"). However, this work is just in its initial stages, with many issues to be addressed such as how to lower the operating temperature, reduce sensitivity to moisture, reduce costs, and ensure reversibility over an adequate lifetime.
Ed |
