Researchers from the Rice University in Houston, Texas have discovered that a class of material known as metallacarborane can be used as a storage material that can lead to more efficient fuel cells.
Metallacarboranes are molecules that combine boron, carbon and metal atoms in a cage-like structure.
Boris Yakobson, a professor in mechanical engineering and materials science and chemistry, and his colleagues suggest that a matrix of these molecules could hold up to 8.8 percent of its weight in hydrogen atoms, possibly surpassing the benchmark set by the United States Department of Energy’s Hydrogen Program for 2015.
«A single metal atom can bind multiple hydrogen molecules,» Mr. Yakobson explained, «but metals also tend to aggregate. Without something to hold them, they clump into a blob and are useless.»
This is where the boron comes in. Boron clusters would grip the titanium and scandium, which would in turn bind hydrogen. Carbon would link the clusters to form a matrix called a metal organic framework, which would act like a sponge for hydrogen
The researchers evaluated various transition metals and found that titanium and scandium have the highest rate of adsorption or the adhesion of transient molecules such as hydrogen to a surface. Both metals also demonstrate the Kubas interaction, a trading of electrons that can bind atoms to one another in certain circumstances.
«Kubas is a special interaction that you often see mentioned in hydrogen research, because it gives exactly the right binding strength,» Mr. Yakobson said.
The Kubas interaction allows for reversible storage of hydrogen in ambient conditions. With a little change in conditions, such as heating up or reducing the pressure of the metals, the hydrogen can be released. This characteristic makes metallacarborane materials highly attractive for daily use in fuel cells.
The findings of the research were published online in the Journal of the American Chemical Society. The Robert Welch Foundation and the Department of Energy supported the study.
