Nanotube defects equal better energy and storage systems

November 19, 2009

Mark Hoefer (left), a UCSD materials science grad student, and mechanical

engineering professor Prabhakar Bandaru have discovered that defects in carbon

nanotubes could lead to supercapacitors that could possibly be used for portable

electronic devices such as cell phones.

Carbon nanotubes could serve as supercapacitor electrodes with enhanced charge and energy storage capacity

(inset: a magnified view of a single carbon nanotube). Credit: UC San Diego

(PhysOrg.com) -- Most people would like to be able to charge their cell phones and other personal electronics quickly and not too often. A recent discovery made by UC San Diego engineers could lead to carbon nanotube-based supercapacitors that could do just this.

In recent research, published in Applied Physics Letters, Prabhakar Bandaru, a professor in the UCSD Department of Mechanical and Aerospace Engineering, along with graduate student Mark Hoefer, have found that artificially introduced defects in nanotubes can aid the development of supercapacitors.

"While batteries have large storage capacity, they take a long time to charge; while electrostatic capacitors can charge quickly but typically have limited capacity. However, supercapacitors/electrochemical capacitors incorporate the advantages of both," Bandaru said.

Carbon nanotubes (CNTs) have been generally hailed as one of the wonder materials of the 21st century and have been widely recognized as ushering in the nanotechnology revolution. They are cylindrical structures, with diameters of 1 to 100 nanometers, that have been suggested to have outstanding structural, chemical, and electrical, characteristics based on their atomically perfect structures with a large surface area-to-volume ratio. However, defects are inevitable in such a practical structure, an aspect that was first investigated by UCSD engineering graduate student Jeff Nichols and then substantially extended by Hoefer in Bandaru's lab.

"We first realized that defective CNTs could be used for energy storage when we were investigating their use as electrodes for chemical sensors," Hoefer said. "During our initial tests we noticed that we were able to create charged defects that could be used to increase CNT charge storage capabilities."

Specifically, defects on nanotubes create additional charge sites enhancing the stored charge. The researchers have also discovered methods which could increase or decrease the charge associated with the defects by bombarding the CNTs with argon or hydrogen.

"It is important to control this process carefully as too many defects can deteriorate the electrical conductivity, which is the reason for the use of CNTs in the first place. Good conductivity helps in efficient charge transport and increases the power density of these devices," Bandaru added.

"At the very outset, it is interesting that CNTs, which are nominally considered perfect, could be useful with so many incorporated defects," he added.

The researchers think that the energy density and power density obtained through their work could be practically higher than existing capacitor configurations which suffer from problems associated with poor reliability, cost, and poor electrical characteristics.

Bandaru and Hoefer hope that their research could have major implications in the area of energy storage, a pertinent topic of today. "We hope that our research will spark future interest in utilizing CNTs as electrodes in charge storage devices with greater energy and power densities," Hoefer said.

While more research still needs to be done to figure out potential applications from this discovery, the engineers suggest that this research could lead to wide variety of commercial applications, and hope that more scientists and engineers will be compelled to work in this area, Bandaru said.

Meanwhile, Hoefer said this type of research will help fuel his future engineering career.

"It is remarkable how current tools and devices are becoming increasing more efficient and yet smaller due to discoveries made at the nanoscale," he said. "My time spent investigating CNTs and their potential uses at the Jacobs School will prepare me for my career, since future research will continue the trend of miniaturization while increasing efficiency."

More information: “Determination and enhancement of the capacitance contributions in carbon nanotube based electrode systems,” Applied Physics Letters. M. Hoefer and P.R. Bandaru.

Source: University of California - San Diego

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INL, ISU team on nanoparticle production breakthrough

INL chemist Bob Fox and his colleagues at Idaho State University have invented a way to make extremely precise, uniform nanoparticles to order. The breakthrough could help make solar cells more efficient and speed the development of nanotechnology.

INL, ISU team on nanoparticle production breakthrough

by Mike Wall, Research Communications Fellow

Every hour, the sun floods Earth with more energy than the entire world consumes in a year. Yet solar power accounts for less than 0.002 percent of all electricity generated in the United States, primarily because photovoltaic cells remain expensive and relatively inefficient.

View the precision nanoparticles video.

But solar may not be such a marginal power source for long. Chemists at Idaho National Laboratory and Idaho State University have invented a way to manufacture highly precise, uniform nanoparticles to order. The technology, Precision Nanoparticles, has the potential to vastly improve the solar cell and further spur the growing nanotech revolution.

A scientific gold rush
Nanoparticles are motes of matter tens of thousands of times smaller than the width of a human hair. Because they're so small, a large percentage of nanoparticles' atoms reside on their surfaces rather than in their interiors. This means surface interactions dominate nanoparticle behavior. And, for this reason, they often have different characteristics and properties than larger chunks of the same material.

While scientists have just begun to exploit nanoparticles, they already show great promise in a number of fields, from medicine to manufacturing to energy. For example, embedding certain nanoparticle types in building materials makes structures stronger and more corrosion-resistant. And nano-engineered transistors are smaller, faster and more efficient than traditional ones.

"Nanoparticles are the scientific gold rush of the next generation," says INL chemist Bob Fox, who helped develop the Precision Nanoparticles technology. "They'll change our lives the way personal computers have."

Because the properties of nanoparticles are so size-dependent, any little dimensional tweak can make a big difference. Thus a key to harnessing the potential of nanoparticles lies in the ability to produce them at certain prescribed sizes, with tiny margins of error. This capability has proven elusive, but it is just what Precision Nanoparticles delivers.

Precision Nanoparticles could enable photovoltaic cells to harness a much bigger chunk of the sun’s radiation spectrum. View a larger version of the solar spectrum.

A new way to make nanoparticles
A few years ago, Fox and ISU chemists Joshua Pak and Rene Rodriguez began looking for a better way to make semiconducting components for solar cells. Specifically, they wanted to improve how raw materials are transformed into semiconducting nanoparticles. The industry's established method of doing this is relatively imprecise and energy-intensive, requiring temperatures around 300 degrees Celsius.

The team hit upon the idea of using "supercritical" carbon dioxide to streamline the reaction. Supercritical fluids are a bit like a mix between a gas and a liquid. They can diffuse through solids, for example, but also dissolve substances like a liquid does. Supercritical carbon dioxide has been used for years to decaffeinate coffee.

But when Fox, Pak and Rodriguez introduced supercritical carbon dioxide into their reaction vessel, the only immediately noticeable result was a thick yellow goop.

"We thought it was a failed experiment," Fox says.

But when the chemists looked more closely, they discovered the goop was full of very small, incredibly uniform semiconducting nanoparticles. The same reaction, roughly, that industry uses to transform raw materials into semiconducting nanoparticles had taken place — but it generated a better, less variable product.

"We didn't expect that doing this would give us such homogeneity," Fox says. "That was really exciting." And because the new reaction could proceed at a much lower temperature — 65 degrees Celsius rather than 300 — it also promised to save a great deal of money and energy.

After tinkering with the reaction, Fox, Pak and Rodriguez figured out how to control nanoparticle size with unprecedented precision. They can now produce prescribed particles between 1 and 100 nanometers, hitting the mark every time with great accuracy. In July, R&D magazine recognized the breakthrough technology as one of its top 100 innovations of 2009 — a prestigious award commonly referred to as an "Oscar of invention". And in September, the work won the Early-Stage Innovation of the Year prize in the Stoel Rives Idaho Innovation Awards.

Fox, Pak and Rodriguez have licensed the technology to Precision Nanoparticles, Inc. The relatively new Seattle company is poised to begin production of tailor-made nanoparticles for the photovoltaic industry.

The chemists have manufactured nanoparticles of the semiconductor copper indium sulfide (identified here as “quantum dots”), a key component of advanced solar cells.

A better solar cell
The aims of the INL and ISU chemists — and of Precision Nanoparticles, Inc. — are to make solar cells more efficient and, ultimately, solar energy more practical.

In a solar cell, photons strike atoms of a semiconducting material — historically, silicon — knocking loose some electrons. These liberated electrons then flow in a single direction, generating direct-current electricity. The amount of energy needed to jar electrons loose is specific to each material and corresponds to only a tiny sliver of the sun's radiation spectrum. This fact explains why the efficiency of most current cells maxes out at around 20 percent.

To knock an electron free from silicon, for example, an incoming photon must have an energy of about 1.3 electron volts. This energy is known as silicon's band gap, and it corresponds to a photon wavelength of 950 nanometers or so. Photons with lower energies — and thus longer wavelengths — won't do the job. Shorter-wavelength photons will, but their energy above 1.3 electron volts is wasted, dissipated as heat. This is a big deal, because the most abundant photons from sunlight occur between 500 and 600 nanometers (which our eyes register as greens and yellows) — meaning that most current photocells waste a lot of energy.

Engineers have been working hard to harness more of the solar spectrum, to design cells that put low-energy photons to work and use high-energy photons more efficiently. One way to do this is to build composite cells with layers of different semiconductors. Slapping a film of copper indium sulfide atop a band of silicon, say, increases a cell's photon-catching power. But building such devices is expensive and technologically tricky.

"The different layers don't play well together," Fox says.

That's where the Precision Nanoparticles technology comes in. One of the many properties that changes with a nanoparticle's size is its band gap. Because Fox and his team learned how to control nanoparticle dimensions so precisely, it may soon be possible to manufacture — from a single material — semiconductor building blocks tuned to specific wavelengths of light. A photovoltaic cell made of such building blocks could capture huge swathes of the solar energy spectrum. And since the cells would contain only a single semiconducting material, they would be much cheaper, more efficient and easier to construct than current multi-layer designs.

Some cells' semiconductor nanoparticles, Fox believes, could even be tuned to pick up infrared wavelengths — heat, which radiates off rocks, buildings, roads and parking lots deep into the night.

"So your solar panel could be working long after you've gone to bed," he says.

The production process is environmentally friendly: it generates little waste and can proceed at relatively low, energy-saving temperatures.

Beyond solar power
While Precision Nanoparticles' most immediate applications come in the field of its birth, photovoltaics, potential uses don't stop there. For example, the technology could also greatly advance ultracapacitor research. Ultracapacitors store electrical energy quickly and effectively, and they may someday replace batteries in electric cars and plug-in hybrids. At least one material, vanadium nitride, has much higher ultracapacitance in nano-form — but only if the nanoparticles are of strictly uniform size, Fox says.

To fully blossom, the nanotech revolution will require the control needed to produce such uniformity. Technologies like that developed by Fox, Pak and Rodriguez may be able to provide this control, delivering particles of predictable size with predictable properties. As a result, nanoparticles could find their way into more designs, and more products.

"The only thing limiting us at this point is our imagination," Fox says.

Electric Buses Of the Future/Ultracapacitor/CNTs

Recharging would be done at solar-paneled bus stops.

By Emily Canal
Thursday, October 15, 2009

A popular sight from Shanghai will be brought to American University on Oct. 21, to present a green alternative to public transportation. The zero-carbon ultracapacitor bus, a vehicle powered completely by batteries capable of charging in minutes, will be unveiled at the event.

"I hope that we can educate people about technology as much as we can save the environment," said Dan Ye, the executive director of Sinautec Automobile Technologies based in Arlington. "I hope that we can replace a lot of diesel vehicles."

The ultracapacitor is a device placed inside the bus that can be recharged quickly to power the vehicle to the next destination. The model bus to be presented at American University can travel 45 miles between charges. There are also batteries placed on board to serve as a reserve energy source.

Ye said one of the advantages of the ultracapacitor is it can recharge in five to 20 minutes, compared to the three hours it can take regular buses. The battery can also be reused between 50,000 and 500,000 cycles.

"It can outlast the entire lifetime of the vehicle," Ye said. "Even after the vehicle has retired you can use the system for other applications."

Overhead chargers would be built at stops and would connect with the vehicles to give the bus the juice needed to drive to the next destination. Shanghai has been using this technology since 2006.

"The version we are showing is the version operating in Shanghai," Ye said. "I hope that in two to three years that we can ramp up the amount of power put into the vehicle using technology coming out of MIT."

Sinautec has teamed up with entities like MIT and the Stella Group, Ltd. to build a version of the bus for the streets of Washington, D.C.

"I find it exciting and more than just a job," said Joel Schindall, a professor of the electrical engineering department at MIT. "We are running out of our energy reserve … and I think it would really be an important step forward."

Schindall is also serving as the principal investigator with a group at MIT to find a way for the ultracapacitor to store more energy. Although no official contracts have been signed between Sinautec and Schindall’s group, Schindall will be speaking at the event about the carbon nanotube enhanced ultracapacitor.

"The ultracapacitor could store more energy, and right now that’s a limiting factor," Schindall said. "The buses can make good use of the ultracapacitor, but they have to be recharged frequently."

Schindall said the nanotubes are carbon atoms that look like tubular rods and resemble shag carpeting. The array of nanotubes has more surface area and can store more energy.

"I think one of the hardest things is the vicious cycle any product that is new and made in small quantities is going to cost more than a mature product," Schindall said. "It will get started but it will be a slow process."

Ye said a typical bus in New York costs between $.70 to $1 per mile for diesel to operate, and the bus usually travels about 100 miles a day. The ultracapacitor would cut carbon emission by 70 percent and cost about $.15 to $.20 to operate per mile.

"Electricity is much cheaper and if you look at the costs of the entire lifetime you would make all the money back," Ye said. "The demonstration would show that this technology is possible and its possible to run carbon free."

Scott Sklar, president of the Stella Group, Ltd. is working with the project to help add solar charging to the bus stations.

"The technology of the 1800s was great, but this is the 21st century and its time to move on," Sklar said. "I like horse and buggies and it was great technology but not in the Capital Beltway."

Sklar said the ground solar panels would face south and resemble bleachers. As passengers boarded the bus, the electronic control equipment would plug in and charge the vehicle.

Sklar said the charging process is great for popular bus stations where it takes several minutes for passengers to get on and off the vehicle. He expects the bus will need five to seven minutes to recharge.

"This is good for people who are not exposed to this stuff," Sklar said. "You can come and touch it and see it’s not as scary as it sounds."

Source

Sinautec Automobile Technologies

Forty One Seat Ultracap Bus Eleven Seat Minibus Ultracap Golf Cart Photo Gallery U.S. Oil Usage

36 FEET ULTRACAPACITOR BUS CHARGING STATION DESIGNS 11 SEAT UNTRACAPACITOR MINI-BUS 4 SEAT UNTRACAPACITOR CART Back to Top

Vehicle Size: 37 Feet 6 Inches Length
8 Feet 2 Inches Width
11 Feet 1 Inch Height
41 Passengers
Maximum Speed: 30 MPH
Power Source: 5.9 KWH Ultracapacitors
Electric Usage: 1.5 KWH per Mile
Recharging Time: 5-10 Minutes*
Maximum Range 3.5 Miles with full air conditioning
5.5 Miles without air conditioning
Bus Weight 12.5 Tons
Acceleration: 4 Feet / Second
Maximum Slope: 12 Degrees
Voltage & Current: 600-720V, 200A
Air Conditioning: 15 KW Air Conditioning
Vehicle Life: 8-12 Years
* Charging time varies depending on charging station voltage.


Ultracap Hybrid Bus
Ideal for on-campus shuttle or urban municipal bus lines. Compare to the Ultracap Bus, Ultracap-Battery Hybrid Bus offers the advantage of extended range.

Vehicle Size: 37 Feet 6 Inches Length
8 Feet 2 Inches Width
11 Feet 1 Inch Height
41 Passengers
Maximum Speed: 33 MPH
Power Source: 2.25 KWH Ultracapacitors**
60 KWH Lead Acid Batteries***
Electric Usage: 1.5 KWH per Mile
Recharging Time: 5-10 Minutes for Ultracapacitors*
6 hours for Lead Acid Batteries
Maximum Range 45 Miles with full air conditioning
Bus Weight 12.5 Tons
Acceleration: 4 Feet / Second
Maximum Slope: 12 Degrees
Voltage & Current: 600-720V, 200A
Air Conditioning: 11.6 KW Air Conditioning
Vehicle Life: 8-12 years
Battery Replacement Every 18 Months
** Lead Acid Battery-Ultracapacitor ratio can be customized to fit client's needs
*** Other Forms of Batteries available
Source

Sinautec is an Arlington, Virginia-based company that develops high energy density ultracapacitors in the transportation and utility energy storage markets. With its research partner, Shanghai Aowei Technology Development Company, Sinautec successfully developed a series of ultracapacitor municipal buses that have been in commercial use in the greater Shanghai area since 2006. “It is our goal to contribute to the Obama Administration’s efforts to improve the environment and to reduce America’s reliance on foreign oil,” said Mr. Ye.
Source

Shanghai Aowei Technology Development Company Patent Position
(Supercapacitor + carbon and/or nanotube)

Schindall ultracapacitor patent filings:
WO 2007131217
US Patent Application 20070258192

What is claimed is:

1) Engineered structure for charge storage comprising: an electrolyte disposed between two electrically conducting plates, each plate serving as a base for an aligned array of electrically conducting nanostructures extending from the surface of each plate into the electrolyte, the nanostructures having diameters and spacing comparable to the dimension of an ion of the electrolyte; and an electrically insulating separator between the two plates.

2) The engineered structure of claim 1 wherein the nanostructures are nanotubes.

3) The engineered structure of claim 2 wherein the nanotubes are single-wall nanotubes.

4) The engineered structure of claim 3 wherein the single wall nanotubes have a length in the range of 60 to 500 μm.

MIT - Technology Review Article:
Next Stop: Ultracapacitor Buses
A U.S.-Chinese venture is out to prove the benefits of quick-charge buses.

Graphene for the Green Grid

Thursday, February 05, 2009

Ultracapacitors that store more could help the grid run smoothly.

By Katherine Bourzac

Graphene power: Graphene Energy hopes that graphene electrodes such as this one will increase the energy-storage capacity and power output of ultracapacitors. This image, which shows the edge of a graphene electrode, was made with a scanning-electron microscope.
Credit: Meryl Stoller

Integrating irregular sources of renewable energy, such as wind and solar, with the electrical grid, while keeping power output steady, is going to be a big challenge. Energy-storage devices called ultracapacitors could help by storing sudden surges of power. But much will depend on developing a new generation of ultracapacitors with enough storage capacity to meet the likely demand.

Graphene Energy, a startup based in Austin, TX, hopes that ultracapacitors with electrodes made of graphene--sheets of carbon just an atom thick--will be the solution. The storage capacity of an ultracapacitor is limited only by the surface area of its electrodes, and graphene offers a way to greatly increase the area available.

Ultracapacitors store energy electrostatically, instead of chemically, as in batteries. During charging, electrons come to the surface of one electrode, and electron "holes" form on the surface of the other. This draws positive ions in an electrolyte to the first electrode and negative ions to the second. By contrast, the chemical reactions used to charge batteries limit the speed with which they can be charged and eventually cause the electrode materials to break down. Ultracapacitors can be charged and discharged very rapidly, in seconds rather than minutes, and can be recharged millions of times before wearing out.

However, ultracapacitors currently on the market can't match batteries for energy density, so they're mostly used in hybrid systems alongside batteries or for niche applications. Because these devices can handle a rapid influx of large amounts of energy, they're often used to recover energy--for example, when a city bus breaks or a gantry crane lowers its cargo. Ultracapacitors employed in this way have reduced by 40 percent the energy needed by some cranes used in Japanese ports. A few power tools, including an electric drill, take advantage of the rapid recharging ability of ultracapacitors.

Graphene Energy hopes to open up new ultracapacitor applications by developing devices with far higher power output. These ultracapacitors could perhaps be used to regulate surges in the electrical grid or to power hybrid transportation vehicles. The company has $500,000 in seed funding to commercialize graphene ultracapacitors developed by Rodney Ruoff, a professor and chair of mechanical engineering at the University of Texas at Austin. Ruoff is a cofounder of Graphene Energy and also serves as the company's technology advisor.

Existing ultracapacitors use electrodes made from activated carbon--a porous, charcoal-like material that has a very high surface area. Activated carbon stores charge in tunnel-like pores, and it takes about one second for it to travel in and out. This is very fast compared with the fastest batteries, but activated carbon has a limited power output.

To make the graphene for its electrodes, Ruoff's team starts by putting graphite oxide in a water solution. This causes the material to flake into atom-thin sheets of graphene oxide. Next, the oxygen atoms are removed, leaving the graphene behind. So far, Ruoff's lab has made graphene ultracapacitors that match the performance of those made using activated carbon. With further refinements, he says, they should outperform activated carbon, although the steps that his company is taking to achieve this remain secret.

Based on a description of the graphene ultracapacitors published last September in the journal Nano Letters, John Miller of JME, a research and consulting firm that specializes in electrochemical capacitors, says that it should indeed be possible to improve their performance. The graphene electrode described in this paper is "wadded into a ball like a crumpled piece of paper," says Miller. "You don't have full access to the surface."

If Graphene Energy can grow the electrodes in vertical arrays, like a row of perfectly flat sheets of paper standing on edge, Miller says that the power output could be increased dramatically. In this arrangement, every single carbon atom would be exposed and able to store energy, with virtually no waiting time for the charge to travel down the tunnels found in activated carbon.

However, in addition to improving the performance of its ultracapacitors, Graphene Energy must also develop a method for making them at larger scales--a common challenge across all graphene research.

Dileep Agnihotri, CEO of Graphene Energy, says that the company hopes to test its first prototype product incorporating graphene electrodes by the end of this year.

Another group of researchers hopes to make better ultracapacitor electrodes using carbon nanotubes--rolled-up tubes of graphene that have many of the same properties. "I think both approaches can work in principle," says Joel Schindall, a professor of electrical engineering and computer science at MIT who is working on the nanotube electrodes. "The key will be getting the growth process right, then working on ways to manufacture it in a cost-effective manner."

http://www.technologyreview.com/business/22062/?nlid=1752&a=f

New Carbon Material Shows Promise of Storing Large Quantities of Renewable Electrical Energy

September 16, 2008

AUSTIN, Texas — Engineers and scientists at The University of Texas at Austin have achieved a breakthrough in the use of a one-atom thick structure called "graphene" as a new carbon-based material for storing electrical charge in ultracapacitor devices, perhaps paving the way for the massive installation of renewable energies such as wind and solar power.

The researchers believe their breakthrough shows promise that graphene (a form of carbon) could eventually double the capacity of existing ultracapacitors, which are manufactured using an entirely different form of carbon.

"Through such a device, electrical charge can be rapidly stored on the graphene sheets, and released from them as well for the delivery of electrical current and, thus, electrical power," says Rod Ruoff, a mechanical engineering professor and a physical chemist. "There are reasons to think that the ability to store electrical charge can be about double that of current commercially used materials. We are working to see if that prediction will be borne out in the laboratory."

Two main methods exist to store electrical energy: in rechargeable batteries and in ultracapacitors which are becoming increasingly commercialized but are not yet as popularly known. An ultracapacitor can be used in a wide range of energy capture and storage applications and are used either by themselves as the primary power source or in combination with batteries or fuel cells. Some advantages of ultracapacitors over more traditional energy storage devices (such as batteries) include: higher power capability, longer life, a wider thermal operating range, lighter, more flexible packaging and lower maintenance, Ruoff says.

Ruoff and his team prepared chemically modified graphene material and, using several types of common electrolytes, have constructed and electrically tested graphene-based ultracapacitor cells. The amount of electrical charge stored per weight (called "specific capacitance") of the graphene material has already rivaled the values available in existing ultracapacitors, and modeling suggests the possibility of doubling the capacity.

"Our interest derives from the exceptional properties of these atom-thick and electrically conductive graphene sheets, because in principle all of the surface of this new carbon material can be in contact with the electrolyte," says Ruoff, who holds the Cockrell Family Regents Chair in Engineering #7. "Graphene's surface area of 2630 m²/gram (almost the area of a football field in about 1/500^th of a pound of material) means that a greater number of positive or negative ions in the electrolyte can form a layer on the graphene sheets resulting in exceptional levels of stored charge."

The U.S. Department of Energy has said that an improved method for storage of electrical energy is one of the main challenges preventing the substantial installation of renewable energies such as wind and solar power. Storage is vital for times when the wind doesn't blow or the sun doesn't shine. During those times, the stored electrical energy can be delivered through the electrical grid as needed.

Ruoff's team includes graduate student Meryl Stoller and postdoctoral fellows Sungjin Park, Yanwu Zhu and Jinho An, all from the Mechanical Engineering Department and the Texas Materials Institute at the university. Their findings will be published in the Oct. 8 edition of Nano Letters. The article was posted on the journal's Web site this week.[See below]

This technology, Stoller says, has the promise of significantly improving the efficiency and performance of electric and hybrid cars, buses, trains and trams. Even everyday devices such as office copiers and cell phones benefit from the improved power delivery and long lifetimes of ultracapacitors.

Ruoff says significant implementation of wind farms for generation of electricity is occurring throughout the world and the United States, with Texas and California first and second in the generation of wind power.

According to the American Wind Energy Association, in 2007 wind power installation grew 45 percent in this country. Ruoff says if the energy production from wind turbine technology grew at 45 percent annually for the next 20 years, the total energy production (from wind alone) would almost equal the entire energy production of the world from all sources in 2007.

"While it is unlikely that such explosive installation and use of wind can continue at this growth rate for 20 years, one can see the possibilities, and also ponder the issues of scale," he says. "Electrical energy storage becomes a critical component when very large quantities of renewable electrical energy are being generated."

Funding and support was provided by the Texas Nanotechnology Research Superiority Initiative, The University of Texas at Austin and a Korea Research Foundation Grant for fellowship support for Dr. Park.

Learn more about Ruoff's work.

For more information, contact: Daniel Vargas, Cockrell School of Engineering, 512-471-7541; Rodney Ruoff, Department of Mechanical Engineering, Cockrell School of Engineering, 512-471-4691, 847-370-4637 (cell).

Source

Graphene-Based Ultracapacitors
Meryl D. Stoller, Sungjin Park, Yanwu Zhu, Jinho An, and Rodney S. Ruoff
Web Release Date: 13-Sep-2008; (Letter) DOI: 10.1021/nl802558y

Abstract Full: HTML / PDF (1703K)
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