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
University of Illinois Researchers Demonstrate Innovative Approaches to Lower Photovoltaic Panel Production Costs
Even if silicon is actually the industry common semiconductor in the majority of electric products, including the solar cells that photovoltaic panels employ to convert sunshine into electricity, it is not really the most effective material readily available. For instance, the semiconductor gallium arsenide and related compound semiconductors offer practically two times the performance as silicon in solar units, however they are rarely utilized in utility-scale applications because of their high production value.
University. of Illinois. teachers J. Rogers and X. Li discovered lower-cost ways to produce thin films of gallium arsenide which also granted usefulness in the types of units they might be incorporated into.
If you can minimize substantially the cost of gallium arsenide and other compound semiconductors, then you could increase their variety of applications.
Typically, gallium arsenide is deposited in a single thin layer on a little wafer. Either the desired device is produced directly on the wafer, or the semiconductor-coated wafer is cut up into chips of the preferred dimension. The Illinois group chose to put in multiple levels of the material on a one wafer, making a layered, “pancake” stack of gallium arsenide thin films.
Figure 1 Thin Film Solar
Source: University of Illinois
If you increase ten levels in one growth, you only have to load the wafer once saving substantially on production costs. Current production processes may require ten separate growths loading and unloading with heat range ramp-up and ramp-down adds to time and costs. If you take into account what is necessary for each growth – the machine, the procedure, the time, the people – the overhead saving derived though the new innovative multi-layer approach, a substantial cost reduction is achieved.
Next the scientists independently peel off the levels and transport them. To complete this, the stacks alternate levels of aluminum arsenide with the gallium arsenide. Bathing the stacks in a solution of acid and an oxidizing agent dissolves the layers of aluminum arsenide, freeing the single thin sheets of gallium arsenide. A soft stamp-like device picks up the levels, one at a time from the top down, for shift to one other substrate – glass, plastic-type or silicon, based on the application. Next the wafer could be used again for an additional growth.
By doing this it’s possible to create considerably more material much more rapidly and much more cost effectively. This process could make mass quantities of material, as compared to simply the thin single-layer way in which it is usually grown.
Freeing the material from the wafer additionally starts the chance of flexible, thin-film electronics produced with gallium arsenide or many other high-speed semiconductors. To make products which can conform but still retain higher performance, which is considerable.
In a document published online May 20 in the magazine Nature the group explains its procedures and shows three types of units making use of gallium arsenide chips made in multilayer stacks: light products, high-speed transistors and solar cells. The creators additionally provide a comprehensive cost comparability.
Another benefit of the multilayer method is the release from area constraints, specifically important for photo voltaic cells. As the levels are removed from the stack, they could be laid out side-by-side on another substrate to create a significantly greater surface area, whereas the typical single-layer process confines area to the size of the wafer.
Figure 2 Solar Arsenium
Source: University of Illinois
For solar panels, you want large area coverage to catch as much sunshine as achievable. In an extreme situation we could grow adequate levels to have ten times the area of the traditional.
After that, the team programs to explore more potential product applications and additional semiconductor resources that might adapt to multilayer growth.
About the Source – Shannon Combs publishes articles for the residential solar power savings web log, her personal hobby weblog focused on recommendations to aid home owners to save energy with solar power.
Original post: Green Econometrics
Nov 24, 2013 Home Automations
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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