Monday, December 12, 2011

Carbon foam: The key ingredient of a better battery?

Researchers at Michigan Technological University are working on it. Actually, their design is a twist on what’s called an asymmetric capacitor, a new type of electrical storage device that’s half capacitor, half . It may be a marriage made in heaven.

Capacitors store an electrical charge physically and have important advantages: they are lightweight and can be recharged (and discharged) rapidly and almost indefinitely. Plus, they generate very little heat, an important issue for electronic devices. However, they can only make use of about half of their stored charge.

Batteries, on the other hand, store electrical energy chemically and can release it over longer periods at a steady voltage. And they can usually store more energy than a capacitor. But batteries are heavy and take time to charge up, and even the best can’t be recharged forever.

Enter asymmetric capacitors, which bring together the best of both worlds. On the capacitor side, energy is stored by electrolyte ions that are physically attracted to the charged surface of a carbon anode. Combined with a battery-style cathode, this design delivers nearly double the energy of a standard capacitor.

Now, Michigan Tech researchers have incorporated a novel material on the battery side to make an even better asymmetric capacitor.

Their cathode relies on nickel oxyhydroxide, the same material used in rechargeable nickel-cadmium or nickel-metal hydride batteries. “In most batteries that contain nickel oxyhydroxide, metallic nickel serves as a mechanical support and a current collector,” said chemistry professor Bahne Cornilsen, who had been studying nickel electrodes for a number of years, initially with NASA support. A few years ago, the Michigan Tech team had a chance to experiment with something different: carbon foam.  He suggested replacing the nickel with carbon foam. 

Carbon foam has advantages over nickel. “It’s lighter and cheaper, so we thought maybe we could use it as a scaffold, filling its holes with nickel oxyhydroxide,” said Tony Rogers, associate professor of chemical engineering.

Carbon foam has a lot of holes to fill. “The carbon foam we are using has 72 percent porosity,” Rogers said. “That means 72 percent of its volume is empty space, so there's plenty of room for the oxyhydroxide. The carbon foam could also be made of renewable biomass, and that’s attractive.”

But how many times can you recharge their novel asymmetric capacitor? Nobody knows; so far, they haven’t been able to wear it out. “We’ve achieved over 127,000 cycles,” Rogers said.

Other asymmetric capacitors have similar numbers, but none have the carbon-foam edge that could make them even more desirable to consumers.

“Being lighter would give it a real advantage in handheld power tools and consumer electronics,” said Rogers. Hybrid electric vehicles are another potential market, since an asymmetric capacitor can charge and discharge more rapidly than a normal battery, making it useful for regenerative braking.

Provided by Michigan Technological University (news : web)

'Graphene earns its stripes': New nanoscale electronic state discovered on graphene sheets

Researchers from the London Centre for Nanotechnology (LCN) have discovered electronic stripes, called 'charge density waves', on the surface of the graphene sheets that make up a graphitic superconductor. This is the first time these stripes have been seen on graphene, and the finding is likely to have profound implications for the exploitation of this recently discovered material, which scientists believe will play a key role in the future of nanotechnology. The discovery is reported in Nature Communications, 29th November.

Graphene is a material made up of a single sheet of carbon atoms just one atom thick, and is found in the marks made by a graphite pencil. Graphene has remarkable physical properties and therefore has great technological potential, for example, in transparent electrodes for flat screen TVs, in fast energy-efficient transistors, and in ultra-strong composite materials. Scientists are now devoting huge efforts to understand and control the properties of this material.

The LCN team donated extra electrons to a graphene surface by sliding calcium metal atoms underneath it. One would normally expect these additional electrons to spread out evenly on the graphene surface, just as oil spreads out on water. But by using an instrument known as a scanning tunneling microscope, which can image individual atoms, the researchers have found that the extra electrons arrange themselves spontaneously into nanometer-scale stripes. This unexpected behavior demonstrates that the electrons can have a life of their own which is not connected directly to the underlying atoms. The results inspire many new directions for both science and technology. For example, they suggest a new method for manipulating and encoding information, where binary zeros and ones correspond to stripes running from north to south and running from east to west respectively.

Story Source:

The above story is reprinted from materials provided by University College London - UCL, via AlphaGalileo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

K.C. Rahnejat, C.A. Howard, N.E. Shuttleworth, S.R. Schofield, K. Iwaya, C.F. Hirjibehedin, Ch. Renner, G. Aeppli, M. Ellerby. Charge density waves in the graphene sheets of the superconductor CaC6. Nature Communications, 2011; 2: 558 DOI: 10.1038/ncomms1574

Enzymatic synthesis of pyrrolysine, the mysterious 22nd amino acid

Proteins are key players in many vital processes in living organisms. They transport substances, catalyze , pump ions or recognize signaling molecules. The complexity and variety of proteins is tremendous, in the human body alone there are more than 100,000 different proteins at work. But almost all of them are made up of just twenty different amino acids. Only a few highly specialized proteins additionally contain selenocysteine, the very rare 21st amino acid discovered in 1986.

A big surprise was the discovery of a 22nd amino acid in methane-producing archaea of the family Methanosarcinaceae in 2002: pyrrolysine. It is genetically encoded in a similar manner as that of selenocysteine and the other twenty amino acids. The use the unusual amino acid in proteins that they need for . Pyrrolysine is located in the catalytic center of the proteins and is essential for their function. The process of the archaebacteria would not work without pyrrolysine.

In March 2011, scientists at Ohio State University succeeded in deciphering parts of the manufacturing process of pyrrolysine. They proposed a reaction mechanism suggesting that the enzyme PylB catalyzes the first step of pyrrolysine by converting the amino acid lysine to the intermediate product metyhlornithine. Scientists headed by Michael Groll, Professor of Biochemistry at the TUM-Department of Chemistry, could now elucidate the of PylB using X-ray structure analysis.

To their great surprise, they caught the enzyme literally "in the act": at the time of crystallization the reaction product, methylornithine, had not left the enzyme. It adhered to a confined space, a kind of "reaction vessel", still in connection with the centers of the enzyme responsible for its creation. "That the product was still present in the enzyme, was something special and a great stroke of luck," says Felix Quitterer, a member of the scientific staff at the Department of Biochemistry and lead author of the publication. "We were not only able to directly detect the methylornithine, but also retroactively reconstruct how it is created from the source amino acid lysine."

This reaction was not only hitherto unknown, it is also very difficult to catalyze. It is a cluster of four iron and four sulfur atoms in the active site of the enzyme that is the key to the conversion. "This is a really unusual enzymatic reaction. Up to now no chemist in the laboratory is able to synthesize methylornithine in a one-step reaction starting from lysine," says Michael Groll.

The conversion of lysine to methylornithine is helping scientists to understand how archaebacteria can modify an existing system to enable the formation of a tailored amino acid that, when installed in the appropriate protein, catalyzes a very specific reaction. Researchers can use this knowledge to create artificial amino acids for "custom tailored" enzymes with special properties that could, for example, find applications in industrial biotechnology and medicine.

There is, however, a more fundamental reason for the great interest in the synthesis of the 22nd amino acid: Scientists are hoping to find new clues to the evolutionary development of the amino acid canon. Why does the vast complexity of proteins in descend from only a few natural amino acids, even though the genetic code would be able to encode many more? An answer to this fundamental question on the minimum requirements for life has thus far eluded scientists. Selenocysteine and pyrrolysine are exotic exceptions. But knowledge about their development from the standard helps to come a little closer to the answer.

More information: Crystal structure of methylornithine synthase (PylB): Insights into the pyrrolysine biosynthesis. Felix Quitterer, Anja List, Wolfgang Eisenreich, Adelbert Bacher and Michael Groll, Angewandte Chemie, Early View, 16. Nov. 2011 – DOI:10.1002/ange.201106765

Provided by Technische Universitaet Muenchen

Fully printed carbon nanotube transistor circuits for displays

 Since the invention of liquid crystal displays in the mid-1960s, display electronics have undergone rapid transformation. Recently developed organic light-emitting diodes (OLEDs) have shown several advantages over LCDs, including their light weight, flexibility, wide viewing angles, improved brightness, high power efficiency and quick response.

OLED-based displays are now used in cell phones, digital cameras and other portable devices. But developing a lower-cost method for mass-producing such displays has been complicated by the difficulties of incorporating thin-film transistors that use amorphous silicon and polysilicon into the production process.

Now, researchers from Aneeve Nanotechnologies, a startup company at UCLA's on-campus technology incubator at the California NanoSystems Institute (CNSI), have used low-cost ink-jet printing to fabricate the first circuits composed of fully printed back-gated and top-gated carbon nanotube-based electronics for use with OLED displays. 

The startup includes collaborators from the departments of materials science and electrical engineering at the UCLA Henry Samueli School of Engineering and Applied Science and the department of electrical engineering at the University of Southern California.

In this innovative study, the team made carbon nanotube thin-film transistors with high mobility and a high on-off ratio, completely based on ink-jet printing. They demonstrated the first fully printed single-pixel OLED control circuits, and their fully printed thin-film circuits showed significant performance advantages over traditional organic-based printed electronics.

"This is the first practical demonstration of carbon nanotube-based printed circuits for display backplane applications," said Kos Galatsis, an associate adjunct professor of materials science at UCLA Engineering and a co-founder of Aneeve. "We have demonstrated carbon nanotubes' viable candidacy as a competing technology alongside amorphous silicon and metal-oxide semiconductor solution as a low-cost and scalable backplane option."

This distinct process utilizes an ink-jet printing method that eliminates the need for expensive vacuum equipment and lends itself to scalable manufacturing and roll-to-roll printing. The team solved many material integration problems, developed new cleaning processes and created new methods for negotiating nano-based ink solutions.

For active-matrix OLED applications, the printed carbon nanotube transistors will be fully integrated with OLED arrays, the researchers said. The encapsulation technology developed for OLEDs will also keep the carbon nanotube transistors well protected, as the organics in OLEDs are very sensitive to oxygen and moisture.

The technology incubator at the CNSI was established two years ago to nurture early-stage research and to help speed the commercial translation of technologies developed at UCLA. Aneeve Nanotechnologies LLC has been conducting proof-of-concept work at the tech incubator with the mission of developing superior, low-cost, high-performance electronics using nanotechnology solutions that bridge the gap between emerging and traditional platforms.

The research was published this month in the journal Nano Letters.

Story Source:

The above story is reprinted from materials provided by University of California - Los Angeles.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Pochiang Chen, Yue Fu, Radnoosh Aminirad, Chuan Wang, Jialu Zhang, Kang Wang, Kosmas Galatsis, Chongwu Zhou. Fully Printed Separated Carbon Nanotube Thin Film Transistor Circuits and Its Application in Organic Light Emitting Diode Control. Nano Letters, 2011; : 111122151948003 DOI: 10.1021/nl202765b