Nanotube-reinforced graphene foam found to be highly conductive

The material can support more than 3,000 times its own weight and bounce back to its original height, as well as be made into any shape and size.

Researchers at Texas-based Rice University have tested ‘rebar graphene’ foam as a highly porous, conductive electrode in lithium ion capacitors and found it to be mechanically and chemically stable.

The conductive graphene foam that the university previously developed has been reinforced by carbon nanotubes. It can support more than 3,000 times its own weight and bounce back to its original height, as well as be made into any shape and size, according to the university.

Carbon in the form of atom-thin graphene is among the strongest materials known and is highly conductive. Multi-walled carbon nanotubes are widely used as conductive reinforcements in metals, polymers and carbon matrix composites.

James Tour, a chemist at the university, said: “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.”

The three-dimensional structures were created from a powdered nickel catalyst, surfactant-wrapped multiwall nanotubes and sugar as a carbon source. The materials were mixed and the water evaporated. The resulting pellets were pressed into a steel die and then heated in a chemical vapour deposition furnace, which turned the available carbon into graphene. After further processing to remove remnants of nickel, the result was an all-carbon foam in the shape of the die, in this case a screw. The method should be easy to scale up, according to the university.

Electron microscope images of the foam showed partially unzipped outer layers of the nanotubes had bonded to the graphene, which accounted for its strength and resilience. Graphene foam produced without the rebar could support only about 150 times its own weight while retaining the ability to rapidly return to its full height during tests. However, rebar graphene irreversibly deformed by about 25% when loaded with more than 8,500 times its weight.

The research has been published in the American Chemical Society journal ACS Applied Materials and Interfaces.