Hydrogen could play a role in replacing fossil fuels for transportation in the future, but researchers must develop a way to store and release large amounts of the highly flammable, odorless invisible gas economically and safely. There are materials that can trap relatively large amounts of hydrogen, at normal pressures, but by now they all require high temperature heating to release the hydrogen contained in them.
Hui Wu, a research associate from the University of Maryland working in a cooperative research program at the NIST Center for Neutron Research, has been investigating a new hydrogen storage compound that mixes lithium amide with lightweight metal hydrides. Lithium amide can hold more than 10 percent of hydrogen by weight, well above the 6 percent target set by the U.S. Department of Energy as a 2010 goal for a hydrogen storage material for transportation. The material absorbs and releases hydrogen reversibly, but both absorbing and releasing the hydrogen requires high temperatures and also produces a toxic byproduct, ammonia.
Metal hydrides do also store hydrogen, though not as well, but it’s been shown recently that a combination of the two (lithium amide with lightweight metal hydrides) not only can store large enough quantities of hydrogen but they can also release it at lower temperatures than the lithium amide alone (about 100 degrees Celsius). More than that, they generate much less ammonia.
To understand how the process works, Wu used neutron analysis to figure out the atomic structure of the material, which she saw it consists of layers of calcium between which lithium ions travel very quickly. The easy travel allows the material to transfer the hydrogen at lower temperatures. Also, the hydrogen ions from the amide and hydride mixture combine pretty easy and release the contained hydrogen at lower temperatures without creating very much ammonia.
Wu explains: “I found that the mobility of small ions in the mixed amide-hydride system greatly improves hydrogen storage properties” . “This finding helps us understand how hydrogen travels in and out of these systems and that may lead to a rational development of better materials for hydrogen storage.”
These storage systems are also a step ahead towards hydrogen vehicles, but there are still methods of producing it on demand. Those are to be studies more and humanity will benefit much more from them than from any other.