Researchers at the University of Maryland have demonstrated through computer modeling that graphene can be triggered by an electric field to fold itself into a nifty three-dimensional box that can serve as a container for hydrogen storage and then unfold itself.
The technique could greatly increase a fuel cell's ability to store and release hydrogen -- an advance that could improve the capacity of hydrogen fuel cells for powering cars.
The way in which the graphene folds up into a box has been dubbed hydrogenation-assisted graphene origami (HAGO) and involves cutting the graphene into a pattern and then functionalizing it by atomically attaching hydrogen to the carbon atoms of the graphene. The electric field that is used does not trigger the graphene to perform its origami but is used to unfold the structure and then repeat the trick.
“First, a suitably functionalized and patterned graphene can spontaneously fold into a 3-D nanostructure.... No external electric field is needed,” explained Teng Li, an associate professor of mechanical engineering at University of Maryland in an e-mail to Nanoclast. “Second, an electric field can cause the polarization of the graphene, effectively reducing the graphene inter-layer adhesion, which causes the folded nanostructure to unfold. Upon turning off the electric field, the graphene folds up into a box spontaneously again. Such a process can be repeated many times.”
In the research, which was published in the journal ACS Nano(“Hydrogenation-Assisted Graphene Origami and Its Application in Programmable Molecular Mass Uptake, Storage, and Release”), the graphene origami boxes demonstrated remarkable hydrogen storage capabilities. The researchers calculate that graphene origami boxes have a hydrogen storage capacity of 9.7 percent by weight, far exceeding targets set by the U.S. Department of Energy (DOE) -- 5.5 percent by 2017 and 7.5 percent by 2020.
It would seem that nanomaterials are exceeding DOE targets for fuel cells on a pretty regular basis now. However, nanomaterials have a somewhat checkered past with hydrogen storage. At one time, carbon nanotubes were touted as the next big thing in that field, with claims of greater than 50-percent storage capacity.
But it is now generally accepted that the figure is really closer to 1-percent. The problem was that the structures of both carbon nanotubes and fullerenes did not remain stable. This instability has not proven to be a problem with the HAGO boxes.
“Much effort has been dedicated in this research to demonstrate the promising feasibility of the HAGO process, including its robustness to possible manufacturing defects and stability at room temperature,” wrote Li. “We will actively pursue collaborations with experimentalists to actually demonstrate.”
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