James' bond: A graphene / nanotube hybrid

November 27, 2012, Rice University

Seven-atom rings (in red) at the transition from graphene to nanotube make a new hybrid material from Rice University a seamless conductor. The hybrid may be the best electrode interface material possible for many energy storage and electronics applications. Credit: Tour Group/Rice University
(Phys.org)—A seamless graphene/nanotube hybrid created at Rice University may be the best electrode interface material possible for many energy storage and electronics applications.

Led by Rice chemist James Tour, researchers have successfully grown forests of carbon nanotubes that rise quickly from sheets of to astounding lengths of up to 120 microns, according to a paper published today by Nature Communications. A house on an average plot with the same aspect ratio would rise into space.

That translates into a massive amount of , the key factor in making things like energy-storing supercapacitors.

The Rice hybrid combines two-dimensional graphene, which is a sheet of carbon one atom thick, and nanotubes into a seamless three-dimensional structure. The bonds between them are covalent, which means adjacent share electrons in a highly stable configuration. The nanotubes aren't merely sitting on the ; they become a part of it.

Forests of nanotubes grown directly from graphene at Rice University are a hybrid material with a massive surface area, possibly the best material ever for supercapacitors and other electrical applications. The seven-member rings at the base (in red) make the seamless transition from graphene to nanotube possible. Credit: Tour Group/Rice University
"Many people have tried to attach nanotubes to a and it's never gone very well because they get a little electronic barrier right at the interface," Tour said. "By growing graphene on metal (in this case copper) and then growing nanotubes from the graphene, the between the nanotubes and the metal electrode is ohmic. That means electrons see no difference, because it's all one seamless material.

"This gives us, effectively, a very of more than 2,000 square meters per gram of material. It's a huge number," said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science and a co-author with former postdoctoral researcher and lead author Yu Zhu, now an assistant professor at the University of Akron.

Nanotubes are grown from graphene in a process developed at Rice University to create nanoscale odako, so named for the giant Japanese kites they resemble. The material may be the best possible for electrical applications like supercapacitors. Credit: Tour Group/Rice University

Tour said proof of the material's hybrid nature lies in the seven-membered rings at the transition from graphene to nanotube, a structure predicted by theory for such a material and now confirmed through electron microscope images with subnanometer resolution.

Carbon has no peer as a conductive material in such a thin and robust form, especially in the form of graphene or certain types of nanotubes. Combining the two appears to offer great potential for electronic components like fast supercapacitors that, because of the massive surface area, may hold a great deal of energy in a tiny package.

A forest of nanotubes, each just a few nanometers wide, grows from a graphene sheet on copper. The hybrid material created at Rice University has a surface area of more than 2,000 square meters per gram. Credit: Tour Group/Rice University

Rice chemist Robert Hauge and his team made the first steps toward such a hybrid over the past decade. Hauge, a distinguished faculty fellow in chemistry at Rice and co-author of the new work, discovered a way to make densely packed carpets of nanotubes on a carbon substrate by suspending catalyst-laced flakes in a furnace. When heated, the catalyst built carbon nanotubes like skyscrapers, starting at the substrate and working their way up. In the process, they lifted the aluminum oxide buffer into the air. The whole thing looked like a kite with many strings and was dubbed an odako, like the giant Japanese kites.

In the new work, the team grew a specialized odako that retained the iron catalyst and aluminum oxide buffer but put them on top of a layer of graphene grown separately on a copper substrate. The copper stayed to serve as an excellent current collector for the three-dimensional hybrids that were grown within minutes to controllable lengths of up to 120 microns.

A plateau of nanotubes grown seamlessly from graphene at Rice University. The hybrid material may be the most efficient ever made for supercapacitors. Credit: Tour Group/Rice University

Electron microscope images showed the one-, two- and three-walled nanotubes firmly embedded in the graphene, and electrical testing showed no resistance to the flow of current at the junction.

"The performance we see in this study is as good as the best carbon-based supercapacitors that have ever been made," Tour said. "We're not really a supercapacitor lab, and still we were able to match the performance because of the quality of the electrode. It's really remarkable, and it all harkens back to that unique interface."

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not rated yet Nov 27, 2012
There was recently announced the ability to make arbitrary length and diameter nanotubes as well. They could put nanotubes inside one another to either strengthen structural elements or make gears and bearings.

I would think the graphene/nanotubes findings points the way to being able to make nanomechanical systems as well as various simple electronic elements.
Alexander Riccio
5 / 5 (1) Nov 27, 2012
Best. Article. Name. Ever.
not rated yet Nov 27, 2012
This gives us, effectively, a very high surface area of more than 2,000 square meters per gram of material. It's a huge number

Damn straight thats a big number.
Pair with: http://phys.org/n...rce.html
And things start to get interesting.
not rated yet Nov 27, 2012
wow wow wow!!!
3 / 5 (2) Nov 28, 2012
That huge area per gram makes me wonder whether an artificial lung better and more compact than a biological one could be made. Would a haemoglobin molecule fit in those tubes? A cyclist so equipped would leave a doped Lance Armstrong in the dust.
5 / 5 (2) Nov 28, 2012
Would a haemoglobin molecule fit in those tubes?

Capillaries in the lungs are already on the order that red blood cells can pass through them only in single file (10-15 microns capillary vs. 6-8 microns for red blood cells). Anything smaller and you get a blockage since there is some variability in cell size.

Blood vessels have also the ability to adapt to increased pressure/blood flow by changing their diameter. Nanotubes cannot match that. (There's also the fact that certain hormones can change permeability of the cell walls, to allow increased gas exchange during exercise)

Just saying: Biological systems can't really be reduced to one factor that is most important (e.g. diameter of capillaries). They are systems evolved under multiple pressures to fulfill roles under many different conditions.

Before we start building 'superior' artificial organs we still have quite some way to go.
2 / 5 (1) Nov 28, 2012
Biological systems can't really be reduced to one factor that is most important

Yay. Someone almost gets it.

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