You are browsing the archives of graphene.

One of the editors at Nature has written a good (free) article that provides some of important perspective about the movement of nano-carbon products (fullerenes, carbon nanotubes and, more recently, graphene) from lab to sustainable markets.

Richard Van Noorden, with quotes from a number or researchers and business reps, describes what a tricky path it can be to go from super-promising materials to specific applications to efficiency-scaled production capacity.

He notes that the first of these to emerge, fullerene, has been pretty much a commercial flop. CNTs emerged in the early 1990s and their semiconducting and metallic-type properties, not to mention their ruggedness, has teased R&D groups and investors ever since. But, CNTs electrical properties can be difficult to control and manufacturing pure bulk CNTs in predictable dimensions and orientations has been illusive. The same same problems are being faced with the newer graphene.

The problem with electronics is that a decent and cheaper alternative is readily available: silicon chips. Van Noorden quotes one organic chemist who points out that, “There have been millions and person-years and trillions of dollars put into the development of silicon electronics. Asking graphene to compte with silicon now is like asking a 10-year-old to be a concert pianist because we’ve been giving him piano lessons for the last six years.”

Van Noorden provides an overview of some of the pros and cons of CNTs and graphene in various applications and how the cost-benefit model can shift over time (e.g., graphene looks more promising in touch-screen applications as the cost of indium – and thus ITO  – trends upwards .)

But even in less esoteric applications, such as using CWTs and graphene flakes in composites, these materials that can retail in the hundreds of dollars/kg are competing with substitutes that sell for less than a dollar/kg. Even with an expected stream of science and manufacturing innovations, experts like Lux Research estimate the $/kg for CNTs will only drop by half in the next ten years.

That’s not a blazing speed for price reduction, but one of the experts Van Noorden interviews points out, the arc of now-ubiquitous carbon fiber began very slowly, eventually found usage in less cost-conscious military applications and much later made its way into large-scale commercial usage.

Nevertheless, manufacturers are bringing more and more capacity on line, and as they do so, they will be scrambling for outlets. Some early niches for graphene will emerge like they have for CWTs (Van Noorden speculates that supercapacitors, such as the one I recently wrote about, electrodes and flexible electronics may pay off), but despite the excitement everyone will have to be patient — perhaps very patient — until they see the first truly transformational uses.

Share

SEM of curved graphene sheets (scale bar- 10 µm). Credit: Nano Letters, C. Liu, Zhenning Yu, David Neff, Aruna Zhamu and Bor Z. Jang.

A recent paper by a group of researchers working in the U.S. and China discusses the creation of a supercapacitor whose electrodes are prepared from curvy, single-layer graphene sheets, a method that yields remarkable energy densities. Their work appears in a recent issue of Nano Letters.

A major problem with current supercapacitors in electric vehicle applications is their low energy density compared to batteries. A good supercapacitor might have an energy density of 10 Wh/kg compared to 170 Wh/kg for good lithium-ion batteries or even 35 Wh/kg for a lead-acid battery. On the other hand, the batteries have long recharging times.

The researchers, who are connected with Nanotek Instruments, Angstrom Materials (a spin-off of Nanotek) and the Department of Materials Science and Engineering at the Dalian University of Technology, basically use an approach based on electrical double-layer capacitance that leverages the intrinsic high surface area and capacitance of graphene plus the higher voltages that are possible through the use of ionic liquid electrolytes. Heretofore, EDL capacitors typically have used activated carbon as a high surface area electrode material.

Ordinary single graphene sheets obviously have surfaces that are easy to put in contact with an electrolyte. The problem is that when one is dealing with a bunch of ordinary graphene sheets, they tend to restack themselves. When this occurs, the intergraphene pore sizes greatly limit the accessibility to the electroyte.

This group apparently has gotten around the restacking problem by finding a way – few details are provided - of giving the graphene sheets curves. In brief, they say they use a modified Hummers method to form graphene oxide. Then:

“The suspension was injected into a forced convention oven in which a stream of compressed air was introduced to produce a fluidized-bed situation. Upon removal of the solvent or liquid, we obtained the desired curved graphene sheets.”

This morphology causes the sheets to resist stacking during packing and compression into an electrode structure. They say their method maintains a pore size in the range of 2–25 nm.

So, by making coin-sized capacitor cells using the curved graphene and 1-ethyl-3-methlyimidazolium tetraflouroborate (EMIMBF4), they were able to achieve energy densitites of 85.6 Wh/kg at room temperature and 136 WH/kg at 80°C, measured at a current density of 1 A/g.

These energy densities are comparable to nickel metal hydride batteries — with an important difference: They can be charged or discharged rapidly.

Share

Chemist Martyn Poliakoff of University of Nottingham has featured a graphene edition of the Periodic Table of Videos. The video offers a short introduction of graphene, a reenactment of the initial discovery of the material and graphene’s potential in technology.

Poliakoff is the narrator of a 118-part series of short videos called The Periodic Table of Videos, which is a popular science project intended to familiarize the public with the periodic table. The site is worth checking out. Each short video offers an informative quick lesson in the element presented.

The graphene video is part of the new Molecular Video collection, which also includes a great video on buckminsterfullerence (Buckeyball). Enjoy!

Share

Wang and colleagues used small angle X-ray diffraction and wide-angle X-ray diffraction to observe changes in the molecular structure of wurtzite crystal under pressure.

It may come as a bit of a surprise, but the strongest material in the world isn’t very strong. Subject it to ultra-high pressure, though, and graphite becomes the hardest substance known.

Most materials that transform under high pressure revert to their original structure when the pressure is lifted, losing any useful properties they may have gained when the pressure was on.

Now, by understanding the process behind the transformation itself, researchers have taken a step toward creating a new class of exceptionally strong, durable materials that maintain their high-pressure properties - including strength and superconductivity - in low-pressure environments.

Cornell  University reported that staff scientist at the Cornell High Energy Synchrotron Source Zhongwu Wang and his team focused on wurtzite, a cadmium-selenium crystal in which atoms are arranged in a diamond-like structure and molecules are bonded on the surface. When thin sheets of wurtzite are squeezed under 10.7 gigapascals of pressure, or 107,000 times the pressure on the Earth’s surface, their atomic structure transforms into a rock salt-like structure.

As pressure was applied, Wang and colleagues integrated two X-ray diffraction techniques (small- and large-angle X-ray diffraction) to characterize changes in the crystal’s surface shape and interior atomic structure, as well as the structural change of surface-bonded molecules.

They first discovered that the nanosheets required three times the pressure to undergo the transformation as the same material in larger crystal form.

And adding a bonding molecule called a soft ligand to the surface of the high-pressure nanosheets, the researchers observed the effect of that bonding to the nanosheets’ internal structure, transformation pressure, and spacing.

They also tested the material’s yield strength, hardness and elasticity during the transformation. Understanding how those properties change as the molecules interact could help researchers design stronger, tougher materials, Wang says.

“Now we know how the atoms move. We understand the intermediate procedure,” says Wang. His experimental process could hold promise for understanding the transformation pathway for other compounds as well.

The research appears in the Proceedings of the National Academy of Sciences.

Share

Researchers use electron-beam lithography to microfabricate graphene devices. (Credit: University of Manchester, UK)

Two University of Manchester researchers have been awarded this year’s Nobel Prize for Physics for their work on graphene. The new physics laureates were announced today at the Royal Swedish Academy of Sciences in Stockholm.

Andrei Geim and Konstantin Novoselov extracted graphene from a piece of graphite using regular adhesive tape, according to the Nobel organization. They were able to obtain a flake of carbon in the graphene form, which at the time, 2004, was thought to be unstable.

Novoselov was a postdoctoral associate working with Geim in 2004 when the researchers discovered that they could make atomically thin slabs of carbon by repeatedly cleaving graphite — essentially pencil lead — with adhesive tape. Their 2004 Science paper describing the material and its electrical properties has already been cited more than 3,000 times.

Graphene is the one atom thick mesh of carbon atoms that shows astonishing electron mobility and may be the eventual route to super-fast electronics - particularly as it is more applicable to planar processing than carbon nanotubes.

“Graphene transistors are predicted to be substantially faster than today’s silicon transistors and result in more efficient computers,” the academy said in the citation. “Since it is practically transparent and a good conductor, graphene is suitable for producing transparent touch screens, light panels and maybe even solar cells.”

According to an MIT Tech Review 2009 story on graphene (a very good quick-read on the topic), the history of graphene, at least as a theoretical possibility, goes back to 1947, but there was resistance to research:

Even as Institute Professor Mildred Dresselhaus, her physicist husband Gene, and others were working in the 1960s with multiple layers of graphene, many scientists were saying that such an ultra-thin sheet of matter could never be found or even made. “It was very controversial; there were many people who were skeptical,” about the research, she says.

The Nobel prize comes with an award of about $1.5 million. A video of the announcement can be seen here.

The researchers’ review on the rise of graphene is now available for free at Nature Materials.

We’ve done countless posts on research using graphene and the material’s potential in applications. Some highlights are found below:

Geim to receive Korber prize for graphene discovery

Graphene memory possible?

Video of the week - The sight of individual carbon atoms in motion

MIT calls graphene a “material for all seasons”

Say ‘cheese’ to turn graphite to graphene

New method for graphene growth successful

Share