Dec 31, 2013 Energy Talks
A new magnetic effect was discovered by accident when a UC Berkeley postdoctoral researcher and several students grew graphene on the surface of a platinum crystal. Graphene is a one atom-thick sheet of carbon atoms arranged in a hexagonal pattern, that looks like chicken wire. Examination showed when grown on platinum, the carbon atoms do not perfectly line up with the metal surface’s triangular crystal structure, which creates a strain pattern in the graphene as if it were being pulled from three different directions.
Michael Crommie, professor of physics at UC Berkeley and a faculty researcher at Lawrence Berkeley National Laboratory runs the lab where the discovery was made. Charles Kane and Eugene Mele of the University of Pennsylvania first predicted the appearance of a “pseudomagnetic” field in response to strain in graphene for carbon nanotubes in 1997. Nanotubes are a rolled up form of graphene.
Crommie explains the strain produces small, raised triangular graphene bubbles 4 to 10 nanometers across in which the electrons occupy discrete energy levels rather than the broad, continuous range of energies allowed by the band structure of unstrained graphene. This new electronic behavior was detected spectroscopically by scanning tunneling microscopy. These so-called Landau levels are reminiscent of the quantized energy levels of electrons in the simple Bohr model of the atom.
Crommie said, “This gives us a new handle on how to control how electrons move in graphene, and thus to control graphene’s electronic properties, through strain. By controlling where the electrons bunch up and at what energy, you could cause them to move more easily or less easily through graphene, in effect, controlling their conductivity, optical or microwave properties. Control of electron movement is the most essential part of any electronic device.”
Inventive engineers take note – this opens a new field.
What happens is the electrons within each nanobubble segregate into quantized energy levels instead of occupying energy bands, as in unstrained graphene. The energy levels are identical to those that an electron would occupy if it were moving in circles in a very strong magnetic field, as high as 300 tesla, which is stronger than any laboratory can produce except in brief explosions, said Crommie. For comparison, a magnetic resonance imager uses magnets running at less than 10 tesla, while the Earth’s magnetic field at ground level is only 31 microtesla. The scale, while atom sized on one dimension – is incredible.
Meanwhile over the last year Francisco Guinea of the Instituto de Ciencia de Materiales de Madrid in Spain, Mikhael Katsnelson of Radboud University of Nijmegen, the Netherlands, and A. K. Geim of the University of Manchester, England predicted what they termed a pseudo quantum Hall effect in strained graphene. This is the very quantization that Crommie’s research group has experimentally observed. Boston University physicist Antonio Castro Neto, who was visiting Crommie’s laboratory at the time of the discovery, immediately recognized the implications of the data, and subsequent experiments confirmed that it reflected the pseudo quantum Hall effect predicted earlier.
This is pretty cheerful stuff. Crommie observes, “Theorists often latch onto an idea and explore it theoretically even before the experiments are done, and sometimes they come up with predictions that seem a little crazy at first. What is so exciting now is that we have data that shows these ideas are not so crazy. The observation of these giant pseudomagnetic fields opens the door to room-temperature ‘straintronics,’ the idea of using mechanical deformations in graphene to engineer its behavior for different electronic device applications.”
The catch in all the excitement is the nanobubble experiments performed in Crommie’s laboratory were performed at very low temperature. Crommie notes that the pseudomagnetic fields inside the nanobubbles are so high that the energy levels are separated by hundreds of millivolts, much higher than room temperature. Thus, thermal noise would not interfere with this effect in graphene even at room temperature.
Normally, electrons moving in a magnetic field circle around the field lines. Within the strained nanobubbles, the electrons move in circles in the plane of the graphene sheet, as if a strong magnetic field has been applied perpendicular to the sheet even when there is no actual magnetic field. Apparently, Crommie said, the pseudomagnetic field only affects moving electrons and not other properties of the electron, such as spin, that are affected by real magnetic fields.
There’s a lot of pseudo so far in the press release and the paper’s abstract at Science. But the research effort is measuring the Tesla force. That point focuses attention is a major way. Getting to 10 Tesla requires lots of power and a source without such a power input thirty times as strong is prey worthy of the best minds in science. Should the effect make it beyond microelectronics in scale to say motors, the impact would be huge.
The long term potential isn’t known in precise terms. There is a great deal of further exploration and experimentation to come. Yet the early theory ideas have borne fruit – by accident.
The serendipitous post doc remains un named, but add to paper’s author list Castro Neto and Francisco Guinea, Sarah Burke, now a professor at the University of British Columbia; Niv Levy, now a postdoctoral researcher at the National Institute of Technology and Standards; and graduate student Kacey L. Meaker, undergraduate Melissa Panlasigui and physics professor Alex Zettl of UC Berkeley. It’s a paper that might be worth the reading fee for the inventive engineer.
Here is the original: New Energy and Fuel
Carbon fiber – it’s the current holy grail of structural material for transportation vehicles like airplanes, cars, trucks, busses and rail. Moving the person or the freight is one thing; the thing that moves them is the other. The less the moving thing weighs the more efficient and less energy required.
But carbon fiber is expensive, other than boutique scale products, only the aerospace industry has the economics to make carbon fiber practical. Graphene research might be pointing the way forward.
James Tour, professor of chemistry at Rice University explains graphene isn’t very soluble, partly because of its dimensions, and partly because of its chemistry. Graphene is just one atom thick, but its surface area is huge. “If you want to work with graphene, you’re working dilute, which makes sense, because this is a huge whopping molecule.”
The Rice University researchers have made graphene solutions 10 times more concentrated than any before. They’ve used these solutions to make transparent, conductive sheets similar to the electrodes on visual displays, and they’re currently developing methods for spinning the graphene solutions to generate fibers and structural materials for airplanes and other vehicles that promise to be less expensive than today’s carbon fiber.
Most methods for making graphene start with graphite and involve flaking off atom-thin sheets of graphene, usually using chemical means. Yang Yang, professor of materials science and engineering at the University of California, Los Angeles explains, “The key is to make single-layer graphene, to not destroy it in the process, and to do it in high volume.”
The Rice University researchers are building from know-how using carbon nanotubes. Dispersing the nanotubes in a liquid makes it possible to process them into macroscopic fibers and films. Most solvents are incapable of dispersing carbon nanotubes, but Rice group uses “superacids” such as fuming sulfuric acid and chlorosulfonic acid to disperse them at high concentrations without harming or altering the carbon nanotube sidewalls.
The late Nobel laureate Richard Smalley discovered that highly concentrated sulfuric acid, so strong it’s called a “superacid,” can bring carbon nanotubes into solution by coating their surfaces with ions.
Building SWNT Fiber. Image Credit: Rice Chemical and Biomolecular Engineering. This is the largest image.
The Rice work with nanotube dispersions enabled research on the production of single walled carbon nanotube (SWNT) fibers using a method similar to that used in the industrial production of Kevlar fibers. Highly concentrated nanotube dispersions in acid can be extruded as a continuous filament; removal of the acid in a coagulant bath causes the dispersion to solidify into a solid fiber composed entirely of carbon nanotubes.
Last year, the Rice group, now led by chemist Matteo Pasquali, showed they could use superacid solutions of carbon nanotubes to make fibers hundreds of meters long. The Rice advance in making and processing graphene in solution may make it practical to work with the material at manufacturing scale. The group has successfully contracted with a major chemical company to commercialize the process in hopes of making electrical transmission lines.
Professor Tour says the superacid solution does not degrade the material’s properties. The group has used the solutions to make sheets of graphene with low electrical resistance and is now “full steam ahead” using these solutions to make graphene fibers.
Tour expects the graphene processing method to have two major applications: transparent electrodes and structural materials as it may bring down costs.
Indium tin oxide, the transparent conducting material most commonly found in touch screens and solar cells, is expensive and brittle, says Benji Maruyama, senior materials research engineer at the Air Force Research Laboratory in Ohio. The U.S. Air Force is funding the Rice research. Many groups have demonstrated the advantages of graphene electrodes in terms of conductivity and flexibility; the Rice method should make it possible to manufacture them over large areas.
Second, the process could also be used to bring down the costs of lightweight, tough structural carbon fiber materials. These materials have been around for decades, but they remain expensive because the processes used to manufacture them are complex and result in lost material. Instead of making pure carbon into fibers directly, as in the Rice process, the current process starts with a nitrile polymer fiber that’s heated to turn it into graphite. These fibers are then woven into mats and glued together to make a bulk material. “They’re used in aircraft, but not in automobiles, because the costs are too high,” says Tour. “If we can do this more cheaply and get as good or better properties, there is the potential for a real advance in carbon fibers.”
Pasquali’s group at Rice may well have a commercial scale new way to make carbon fibers and sheets of “conductive circuit boards” and conductors for visual displays. The experience of getting the nanotube process licensed bodes well for some level of commercial production for the graphene based carbon products.
The test remains getting to the economies of commercial scale such that carbon fiber is competitive with heavier materials such as steel and aluminum. Pasquali said some months back, “For transmission lines you need to make tons, and there are no methods now to do that,” he says. “We are one miracle away.”
The graphene acid solution method is looking good. Parts for very strong lightweight transport vehicles might be coming soon.
Original post here: New Energy and Fuel
Carbon is cheap, abundant, and in the form of the nanoparticles graphene, capable of absorbing a wide range of light frequencies. Graphene is essentially the same stuff as a pencil’s graphite, except graphene is formed to a single sheet of carbon, just one atom thick. Graphene shows promise as an effective, cheap-to-produce, and less toxic alternative to other materials currently used in solar cells. But it has also vexed scientists.
For a sheet of graphene to be useful as a solar collector of light photons, the sheet must be large enough. To use the absorbed solar energy for electricity the sheet can’t be made too large. Scientists find large sheets of graphene difficult to work with, and the size specification even harder to control.
The bigger the graphene sheet, the stickier it is, making it more likely to attract and attach onto other graphene sheets. Multiple layers of graphene prevent electricity production.
Indiana University at Bloomington chemists have devised an unusual solution – attach a constructed “3-D bramble patch” to each side of the carbon sheet. With a method newly devised, the IU team say they are able to dissolve sheets containing as many as 168 carbon atoms, a first, that may make large sheets of carbon available for light collection.
The IU team’s report, online April 9, will appear in a future issue of Nano Letters.
Chemist Liang-shi Li, who led the research said, “Our interest stems from wanting to find an alternative, readily available material that can efficiently absorb sunlight. At the moment the most common materials for absorbing light in solar cells are silicon and compounds containing ruthenium. Each has disadvantages.” Ruthenium-based solar cells can potentially be cheaper than silicon-based ones, but ruthenium is a rare metal on Earth, as rare as platinum, and will run out quickly when the demand increases. Cost and availability loom to discourage investment.
The graphene idea has been around a while. Chemists and engineers experimenting with graphene have come up with a whole host of strategies for keeping single graphene sheets separated. The most effective solution prior to the IU team’s paper was breaking up graphite from the top-down into sheets and then wrap polymers around them to keep them isolated from one another. But this approach makes graphene sheets with random sizes that are too large for the light absorption needed for solar cells.
Li and the team tried an innovative idea. By attaching a semi-rigid, semi-flexible, three-dimensional “sidegroup” to the sides of the graphene, they were able to keep graphene sheets as big as 168 carbon atoms from adhering to one another. With the new dynamic method, they could make the graphene sheets from smaller molecules built bottom-up so that they are uniform in size. To the scientists’ knowledge, it is the biggest stable graphene sheet ever made with the bottom-up approach. Check the image below for more detail.
The sidegroup consists of a hexagon shaped carbon ring and three long, barbed tails made of carbon and hydrogen. Because the graphene sheet itself is rigid, the sidegroup ring is forced to rotate about 90 degrees relative to the plane of the graphene. The three “brambly” tails are free to whip about, with two of them tending to enclose the graphene sheet of which they are attached. This makes up a dynamic box or cage for the graphene sheet.
But he tails don’t merely act as a cage; they also serve as a handle for an organic solvent so that the entire structure can be dissolved. Li and his colleagues were able to dissolve 30 mg of the specimens per 30 mL of solvent. The ability to breakdown the graphene is significant as well.
Li said, “In this paper, we found a new way to make graphene soluble. This is just as important as the relatively large size of the graphene itself.” This new know how may make all the difference for building things using graphene across a range of products.
How well does the new graphene assembly work? To test the effectiveness of their graphene light acceptor, the scientists constructed rudimentary solar cells using titanium dioxide as an electron acceptor. The team has been able to achieve a 200-microampere-per-square-cm current density and an open-circuit voltage of 0.48 volts. The graphene sheets absorbed a significant amount of light in the visible to near-infrared range (200 to 900 nm or so) with peak absorption occurring at 591 nm. As black as this kind of thing must be – those are good numbers.
The team is in the process of redesigning the graphene sheets with sticky ends so that they bind to titanium dioxide – a construction that will improve the efficiency of the solar cells.
Liang-shi Li’s team includes PhD students Xin Yan and Xiao Cui and postdoctoral fellow Binsong Li. Along with grants form the National Science Foundation, the American Chemical Society Petroleum Research Fund put money into the research.
This is quite a new start for graphene as a photovoltaic solar collector material. Kicking up the micro amp from a cm² to a meter² is 100 or 200 micro amps then is .02 amps, not a bad start at nearly a half-volt.
Original post: New Energy and Fuel
Nov 10, 2013 Energy Talks
Javad Rafiee, a doctoral student in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer Polytechnic Institute, has developed a new method for storing hydrogen at room temperature. Rafiee seems determined to play a key role in solving global dependency on fossil fuels. The young man is one winner of the 2010 $30,000 Lemelson-MIT Rensselaer Student Prize, of the four 2010 winners announced March 3, 2010.
Rafiee is the fourth recipient of the Lemelson-MIT Rensselaer Student Prize. The prize, first given in 2007, is awarded annually to a Rensselaer senior or graduate student who has created or improved a product or process, applied a technology in a new way, redesigned a system, or demonstrated remarkable inventiveness in other ways.
Hydrogen storage is well known to be a significant problem for the advancement and proliferation of fuel cell and hydrogen technologies in cars, trucks, and other applications. Rafiee has created a novel form of engineered graphene that exhibits hydrogen storing capacity far exceeding any other known material.
The hydrogen storage idea is a development of new method for manufacturing and using graphene, an atom-thick sheet of carbon atoms arranged like a nanoscale chain-link fence, to store hydrogen. The proposed solution is said to be inexpensive and easy to produce.
With adviser and Rensselaer Professor Nikhil Koratkar, Rafiee uses a combination of mechanical grinding, plasma treatment, and annealing to engineer the atomic structure of graphene to maximize its hydrogen storage capacity. The new graphene material exhibits a hydrogen storage capacity of 14 percent by weight at room temperature – far exceeding any other known material.
How big a deal is this? The 14-percent capacity surpasses the U.S. Department of Energy’s 2015 target of realizing a material with hydrogen storage capacity of 9 percent by weight at room temperature. Rafiee said his graphene is also one of the first known materials to surpass the Department of Energy’s 2010 target of 6 percent. This is a big deal indeed.
Rafiee’s graphene exhibits three critical attributes that result in its unique hydrogen storage capacity:
The first is high surface area. Graphene’s unique structure, only one atom thick, means that each of its carbon atoms is exposed to the environment and, in turn, to the hydrogen gas.
The second attribute is low density. Graphene has one of the highest surface area-per-unit masses in nature, far superior to even carbon nanotubes and fullerenes.
The third attribute is favorable surface chemistry. After oxidizing graphite powder and mechanically grinding the resulting graphite oxide, Rafiee synthesized the graphene by thermal shock followed by annealing and exposure to argon plasma. These treatments play an important role in increasing the binding energy of hydrogen to the graphene surface at room temperature, as hydrogen tends to cluster and layer around carbon atoms.
Meanwhile . . . Victor Aristov and colleagues indicate that graphene has the potential to replace silicon in high-speed computer processors and other devices. Standing in the way, however, are today’s cumbersome, expensive production methods, which result in poor-quality graphene and are not practical for industrial scale applications.
Aristov and colleagues report that they have developed “a very simple procedure for making graphene on the cheap.” They describe growing high-quality graphene on the surface of commercially available silicon carbide wafers to produce material with excellent electronic properties. It “represents a huge step toward technological application of this material as the synthesis is compatible with industrial mass production.” Their report is published in Nano Letters.
Aristov is leading an impressive list of researchers from the Leibniz Institute for Solid State and Materials Research in Dresden, Germany, the Institute of Solid State Physics, Russian Academy of Sciences, Moscow District, Russia, the Institute of Solid State Physics, Dresden University of Technology, Dresden, Germany, the MAX-lab, Lund University, Lund, Sweden, and the TASC National Laboratory, INFM-CNR, Trieste, Italy.
Could these two breakthroughs merge or would a technology merger make sense? That’s an unknown for today, but graphene’s raw material, carbon, isn’t exotic, rare or any kind of wildly expensive material. Lots of unanswered question come with the news. The raw material will be a cost, the formation and process techniques will be costs. If the material will cycle hydrogen in and out without limit that’s one thing, but if there are cycling limits the value would be quite different. Then what is involved to get the hydrogen in and back out again?
There’s not enough in the releases to make conclusions, but the new path is clearer. There is a long way to go, but the prospects are intuitively very promising. Hydrogen storage is a major problem and if the young man and the European team both have valid starting points for effective, low cost, long life and energy dense hydrogen storage with hopefully simple and cheap loading and unloading – one’s view on hydrogen fuel production might brighten up dramatically.
Source: New Energy and Fuel