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Graphene shows unusual thermoelectric response to light – MIT News Office.

 

Graphene shows unusual thermoelectric response to light

Finding could lead to new photodetectors or energy-harvesting devices.

Given the enormous scale of worldwide energy use, there are limited options for achieving significant reductions in greenhouse gas emissions.

October 20, 2011

Photo: Len Rubenstein

Graphene, an exotic form of carbon consisting of sheets a single atom thick, exhibits a novel reaction to light, MIT researchers have found: Sparked by light’s energy, the material can produce electric current in unusual ways. The finding could lead to improvements in photodetectors and night-vision systems, and possibly to a new approach to generating electricity from sunlight.

This current-generating effect had been observed before, but researchers had incorrectly assumed it was due to a photovoltaic effect, says Pablo Jarillo-Herrero, an assistant professor of physics at MIT and senior author of a new paper published in the journal Science. The paper’s lead author is postdoc Nathaniel Gabor; co-authors include four MIT students, MIT physics professor Leonid Levitov and two researchers at the National Institute for Materials Science in Tsukuba, Japan.

Instead, the MIT researchers found that shining light on a sheet of graphene, treated so that it had two regions with different electrical properties, creates a temperature difference that, in turn, generates a current. Graphene heats inconsistently when illuminated by a laser, Jarillo-Herrero and his colleagues found: The material’s electrons, which carry current, are heated by the light, but the lattice of carbon nuclei that forms graphene’s backbone remains cool. It’s this difference in temperature within the material that produces the flow of electricity. This mechanism, dubbed a “hot-carrier” response, “is very unusual,” Jarillo-Herrero says.

Such differential heating has been observed before, but only under very special circumstances: either at ultralow temperatures (measured in thousandths of a degree above absolute zero), or when materials are blasted with intense energy from a high-power laser. This response in graphene, by contrast, occurs across a broad range of temperatures all the way up to room temperature, and with light no more intense than ordinary sunlight.

The reason for this unusual thermal response, Jarillo-Herrero says, is that graphene is, pound for pound, the strongest material known. In most materials, superheated electrons would transfer energy to the lattice around them. In the case of graphene, however, that’s exceedingly hard to do, since the material’s strength means it takes very high energy to vibrate its lattice of carbon nuclei — so very little of the electrons’ heat is transferred to that lattice.

Because this phenomenon is so new, Jarillo-Herrero says it is hard to know what its ultimate applications might be. “Our work is mostly fundamental physics,” he says, but adds that “many people believe that graphene could be used for a whole variety of applications.”

But there are already some suggestions, he says: Graphene “could be a good photodetector” because it produces current in a different way than other materials used to detect light. It also “can detect over a very wide energy range,” Jarillo-Herrero says. For example, it works very well in infrared light, which can be difficult for other detectors to handle. That could make it an important component of devices from night-vision systems to advanced detectors for new astronomical telescopes.

The new work suggests graphene could also find uses in detection of biologically important molecules, such as toxins, disease vectors or food contaminants, many of which give off infrared light when illuminated. And graphene, made of pure and abundant carbon, could be a much cheaper detector material than presently used semiconductors that often include rare, expensive elements.

The research also suggests graphene could be a very effective material for collecting solar energy, Jarillo-Herrero says, because it responds to a broad range of wavelengths; typical photovoltaic materials are limited to specific frequencies, or colors, of light. But more research will be needed, he says, adding, “It is still unclear if it could be used for efficient energy generation. It’s too early to tell.”

“This is the absolute infancy of graphene photodetectors,” Jarillo-Herrero says. “There are many factors that could make it better or faster,” which will now be the subject of further research.

Philip Kim, an associate professor of physics at Columbia University who was not involved in this research, says the work represents “extremely important progress toward optoelectric and energy-harvesting applications” based on graphene. He adds that because of this team’s work, “we now have better understanding of photo-generated hot electrons in graphene, excited by light.”

The research was supported by the Air Force Office of Scientific Research, along with grants from the National Science Foundation and the Packard Foundation.

One Sheet Solar Cooker – Appropedia: The sustainability wiki.

One Sheet Solar Cooker

Cocina_Solar_Simple in Spanish / en español.

Cocinasolarsimple.png

http://imagina-canarias.blogspot.com/2008/06/cocina-solar-simple.html 9 june 2008

This is the simplest solar cooker I’ve been able to design:

  1. Use a cardboard sheet 60 cm x 80 cm or larger.
  2. Draw lines to divide in 2×3 parts, and cut “A” lines only.
  3. The dotted lines are all for concave folding, so you can make a careful “half-cut” and then it will be easier to fold.
  4. Make two holes, so that the string will go through the holes once the red parts are below the yellow part. The string is knotted like your shoes’. Not a permanent knot because you want to be able to take the kitchen to other places.
  5. Glue foil paper to the part of the cardboard closer to you. Maybe the inner side of some fried chips bags. If there’s no glue you may staple it.
  6. The bottle with the bottom cut off (and discarded, unless you find a use for it) helps in getting more greenhouse effect. You can place it on a circle made of sand so that it’s more air-tight, so almost no heat should come out there.
  7. Inside the “greenhouse” you could place a glass jar, with its lid. Both the jar and the lid can be painted black with some kind of paint that doesn’t produce toxic vapour when heated. Coal with rice water or something.

Enjoy!

Careful, it’s hot! I don’t think temperature goes above 100ºC. Use folded cloth or gloves to grab the hot jar.

Public domain, so copy, modify and use at will. Experiment and tell us.

New battery design could give electric vehicles a jolt.

New battery design could give electric vehicles a jolt

Significant advance in battery architecture could be breakthrough for electric vehicles and grid storage.

A sample of ‘Cambridge crude’ — a black, gooey substance that can power a highly efficient new type of battery. A prototype of the semi-solid flow battery is seen behind the flask.
Photo: Dominick Reuter June 6, 2011
A radically new approach to the design of batteries, developed by researchers at MIT, could provide a lightweight and inexpensive alternative to existing batteries for electric vehicles and the power grid. The technology could even make “refueling” such batteries as quick and easy as pumping gas into a conventional car.

The new battery relies on an innovative architecture called a semi-solid flow cell, in which solid particles are suspended in a carrier liquid and pumped through the system. In this design, the battery’s active components — the positive and negative electrodes, or cathodes and anodes — are composed of particles suspended in a liquid electrolyte. These two different suspensions are pumped through systems separated by a filter, such as a thin porous membrane.

The work was carried out by Mihai Duduta ’10 and graduate student Bryan Ho, under the leadership of professors of materials science W. Craig Carter and Yet-Ming Chiang. It is described in a paper published May 20 in the journal Advanced Energy Materials. The paper was co-authored by visiting research scientist Pimpa Limthongkul ’02, postdoc Vanessa Wood ’10 and graduate student Victor Brunini ’08.

One important characteristic of the new design is that it separates the two functions of the battery — storing energy until it is needed, and discharging that energy when it needs to be used — into separate physical structures. (In conventional batteries, the storage and discharge both take place in the same structure.) Separating these functions means that batteries can be designed more efficiently, Chiang says.

The new design should make it possible to reduce the size and the cost of a complete battery system, including all of its structural support and connectors, to about half the current levels. That dramatic reduction could be the key to making electric vehicles fully competitive with conventional gas- or diesel-powered vehicles, the researchers say.

Another potential advantage is that in vehicle applications, such a system would permit the possibility of simply “refueling” the battery by pumping out the liquid slurry and pumping in a fresh, fully charged replacement, or by swapping out the tanks like tires at a pit stop, while still preserving the option of simply recharging the existing material when time permits.

Flow batteries have existed for some time, but have used liquids with very low energy density (the amount of energy that can be stored in a given volume). Because of this, existing flow batteries take up much more space than fuel cells and require rapid pumping of their fluid, further reducing their efficiency.

The new semi-solid flow batteries pioneered by Chiang and colleagues overcome this limitation, providing a 10-fold improvement in energy density over present liquid flow-batteries, and lower-cost manufacturing than conventional lithium-ion batteries. Because the material has such a high energy density, it does not need to be pumped rapidly to deliver its power. “It kind of oozes,” Chiang says. Because the suspensions look and flow like black goo and could end up used in place of petroleum for transportation, Carter says, “We call it ‘Cambridge crude.’”

The key insight by Chiang’s team was that it would be possible to combine the basic structure of aqueous-flow batteries with the proven chemistry of lithium-ion batteries by reducing the batteries’ solid materials to tiny particles that could be carried in a liquid suspension — similar to the way quicksand can flow like a liquid even though it consists mostly of solid particles. “We’re using two proven technologies, and putting them together,” Carter says.

In addition to potential applications in vehicles, the new battery system could be scaled up to very large sizes at low cost. This would make it particularly well-suited for large-scale electricity storage for utilities, potentially making intermittent, unpredictable sources such as wind and solar energy practical for powering the electric grid.

The team set out to “reinvent the rechargeable battery,” Chiang says. But the device they came up with is potentially a whole family of new battery systems, because it’s a design architecture that “is not linked to any particular chemistry.” Chiang and his colleagues are now exploring different chemical combinations that could be used within the semi-solid flow system. “We’ll figure out what can be practically developed today,” Chiang says, “but as better materials come along, we can adapt them to this architecture.”

Yury Gogotsi, Distinguished University Professor at Drexel University and director of Drexel’s Nanotechnology Institute, says, “The demonstration of a semi-solid lithium-ion battery is a major breakthrough that shows that slurry-type active materials can be used for storing electrical energy.” This advance, he says, “has tremendous importance for the future of energy production and storage.”

Gogotsi cautions that making a practical, commercial version of such a battery will require research to find better cathode and anode materials and electrolytes, but adds, “I don’t see fundamental problems that cannot be addressed — those are primarily engineering issues. Of course, developing working systems that can compete with currently available batteries in terms of cost and performance may take years.”

Chiang, whose earlier insights on lithium-ion battery chemistries led to the 2001 founding of MIT spinoff A123 Systems, says the two technologies are complementary, and address different potential applications. For example, the new semi-solid flow batteries will probably never be suitable for smaller applications such as tools, or where short bursts of very high power are required — areas where A123’s batteries excel.

The new technology is being licensed to a company called 24M Technologies, founded last summer by Chiang and Carter along with entrepreneur Throop Wilder, who is the company’s president. The company has already raised more than $16 million in venture capital and federal research financing.

The development of the technology was partly funded by grants from the U.S. Department of Defense’s Defense Advanced Research Projects Agency and Advanced Research Projects Agency – Energy (ARPA-E). Continuing research on the technology is taking place partly at 24M, where some recent MIT graduates who worked on the project are part of the team; at MIT, where professors Angela Belcher and Paula Hammond are co-investigators; and at Rutgers, with Professor Glenn Amatucci.

The target of the team’s ongoing work, under a three-year ARPA-E grant awarded in September 2010, is to have, by the end of the grant period, “a fully-functioning, reduced-scale prototype system,” Chiang says, ready to be engineered for production as a replacement for existing electric-car batteries.

I would really like to buy one, if true, this can be an excellent problem solver for us who generate a lot of plastic garbage due to ridiculous over packing culture in France.

Be-h Desk-top Waste Plastic Oiling System

Front Page Back Page

Convenient Home Recycler Turns Plastic Garbage Back Into Ready-To-Use Petroleum

A Japanese inventor has figured out a way to convert plastic grocery bags, bottles and caps back into the petroleum from whence they came, providing a ready fuel source for individual homes that also diverts waste from landfills.

Akinori Ito’s plastic recycling machine heats up waste plastic, traps vapors in a system of pipes and water chambers, and condenses the vapors into crude oil, explains the website Clean Technica. It’s not the first machine to do this — a massive plant outside Washington, D.C., is testing the process, for instance — but it’s small enough for household use.

Ito’s machine turns two pounds of plastic into a quart of oil, using only one kilowatt-hour of energy. The crude oil can be used in some types of generators or it can be further refined into gasoline, Clean Technica reports.

Ito is selling it through his Blest Corp., but buyer beware: As of now, it will set you back about $10,000. Ito hopes the price will drop as demand and production increase.

Other plastic-recycling methods find creative new uses for the material, for instance turning oil booms into new Chevy Volts or building new boats to sail the Pacific. Ito’s invention is interesting because it puts the plastic back into the pipeline, as it were. This is definitely not carbon-neutral — burning the oil releases greenhouse gases — but it’s environmentally friendly in that it can divert non-biodegradable waste from landfills. And make you feel less guilty next time you forget your canvas grocery bags.

Be-h

Capacity:Max 1kg/Time

【 Result of Plastic-to-oil Experiment 】

Equipment : Desk-Top Type Be-h

Lactic Acid Beverage Container
Plastic : PP or PE / Weight : 400g
[Material]

[Produced Oil]

[Result]

Produced Oil:337g(422ml)
Oil Ratio:84.4%
Residue:40g

DVD Case
Plastic : PP / Weight : 1000g
[Material]

[Produced Oil]

[Result]

Produced Oil:808g(1010ml)
Oil Ratio:80.8%
Residue:107g

Artificial Lawn
Plastic : PP / Weight : 860g
[Material]

[Produced Oil]

[Result]

Produced Oil:380g(475ml)
Oil Ratio:44%
Residue:390g

Flexible Container
Plastic : PP & PE / Weight : 700g
[Material]

[Produced Oil]

[Result]

Produced Oil:520g(650ml)
Oil Ratio:74%
Residue:90g

Toy Case
Plastic : PP(Soft Type),PS(Hard Type) / Weight : 600g
[Material]

[Produced Oil]

[Result]

Produced Oil:560g(700ml)
Oil Ratio:93%
Residue,Hydrocarbon Gas:40g

School Meal Plastic(Straw・Wrap of Bread)
Plastic : PP(Straw),PP or PE(Wrap) / Weight : 400g
[Material]

[Produced Oil]

[Result]

Produced Oil:412g(515ml)
Oil Ratio:82.4%
Residue,Hydrocarbon Gas:103g