Graphene spends most of its time in a two-dimensional form, but that makes it hard to make use of its long list of advantages, like its strength, light weight, and electricity and heat conduction. MIT scientists recently developed a 3D version that's 10 times stronger than steel but a fraction of the density, and now a team at Rice University has used carbon nanotubes to reinforce graphene foam. The resulting 3D material can be molded into any shape and supports 3,000 times its own weight before springing back to its original height.

Named for the rebars (reinforcing bars) commonly used to strengthen concrete, Rice's "rebar graphene" is built around carbon nanotubes with several concentric layers. In previous work the team had created three-dimensional graphene foam, and having already used the nanotubes to reinforce regular old 2D graphene, it made sense to combine the two.

"We developed graphene foam, but it wasn't tough enough for the kind of applications we had in mind, so using carbon nanotubes to reinforce it was a natural next step," says James Tour, lead researcher on the study.

The team mixed the nanotubes in with a powdered nickel catalyst and sugar to provide the carbon. Dried pellets of the substance were then pressed in a steel die in the shape of a screw, and the carbon in the sugar was turned into graphene through the process of chemical vapor deposition. Any remaining traces of nickel were removed, and the final result was a pure carbon, screw-shaped piece of graphene foam.

When viewed under an electron microscope, the researchers could see that the outer layers of the nanotubes had started to "unzip" and bonded with the graphene, which allowed the material to hold over 3,000 times its own weight without permanent damage. Even with a burden of 8,500 times its weight, the structure deformed permanently by only 25 percent. By comparison, graphene foam with no supporting nanotube structure began to struggle under a load of just 150 times its own weight.

While graphene foam can be formed into basically any shape, the researchers demonstrated that their creation worked as an electrode in a lithium-ion capacitor, and stayed mechanically and chemically stable.

The research was published in the journal ACS Applied Materials and Interfaces.

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