Electricity and Carbon Dioxide Used to Generate Alternative Fuel

Electricity and Carbon Dioxide Used to Generate Alternative Fuel

  8:10:00 PM    Science Lover

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Imagine being able to use electricity to power your car -- even if it's not an electric vehicle. Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have for the first time demonstrated a method for converting carbon dioxide into liquid fuel isobutanol using electricity.

Producing fuel from CO2 and sunlight. (Credit: Image
courtesy of University of California - Los Angeles)

Today, electrical energy generated by various methods is still difficult to store efficiently. Chemical batteries, hydraulic pumping and water splitting suffer from low energy-density storage or incompatibility with current transportation infrastructure.

In a study published March 30 in the journal Science, James Liao, UCLA's Ralph M. Parsons Foundation Chair in Chemical Engineering, and his team report a method for storing electrical energy as chemical energy in higher alcohols, which can be used as liquid transportation fuels.

"The current way to store electricity is with lithium ion batteries, in which the density is low, but when you store it in liquid fuel, the density could actually be very high," Liao said. "In addition, we have the potential to use electricity as transportation fuel without needing to change current infrastructure."

Liao and his team genetically engineered a lithoautotrophic microorganism known as Ralstonia eutropha H16 to produce isobutanol and 3-methyl-1-butanol in an electro-bioreactor using carbon dioxide as the sole carbon source and electricity as the sole energy input.

Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. There are two parts to photosynthesis -- a light reaction and a dark reaction. The light reaction converts light energy to chemical energy and must take place in the light. The dark reaction, which converts CO2 to sugar, doesn't directly need light to occur.

"We've been able to separate the light reaction from the dark reaction and instead of using biological photosynthesis, we are using solar panels to convert the sunlight to electrical energy, then to a chemical intermediate, and using that to power carbon dioxide fixation to produce the fuel," Liao said. "This method could be more efficient than the biological system."

Liao explained that with biological systems, the plants used require large areas of agricultural land. However, because Liao's method does not require the light and dark reactions to take place together, solar panels, for example, can be built in the desert or on rooftops.

Theoretically, the hydrogen generated by solar electricity can drive CO2 conversion in lithoautotrophic microorganisms engineered to synthesize high-energy density liquid fuels. But the low solubility, low mass-transfer rate and the safety issues surrounding hydrogen limit the efficiency and scalability of such processes. Instead Liao's team found formic acid to be a favorable substitute and efficient energy carrier.

"Instead of using hydrogen, we use formic acid as the intermediary," Liao said. "We use electricity to generate formic acid and then use the formic acid to power the CO2 fixation in bacteria in the dark to produce isobutanol and higher alcohols."

The electrochemical formate production and the biological CO2 fixation and higher alcohol synthesis now open up the possibility of electricity-driven bioconversion of CO2 to a variety of chemicals. In addition, the transformation of formate into liquid fuel will also play an important role in the biomass refinery process, according to Liao.

"We've demonstrated the principle, and now we think we can scale up," he said. "That's our next step."

The study was funded by a grant from the U.S. Department of Energy's Advanced Research Projects Agency-Energy (ARPA-E).

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New Way to Store Sun's Heat: Modified Carbon Nanotubes Can Store Solar Energy Indefinitely, Then Be Recharged by Exposure to the Sun

New Way to Store Sun's Heat: Modified Carbon Nanotubes Can Store Solar Energy Indefinitely, Then Be Recharged by Exposure to the Sun

  12:25:00 AM    Science Lover

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A novel application of carbon nanotubes, developed by MIT researchers, shows promise as an innovative approach to storing solar energy for use whenever it's needed.

Illustration. (Credit: Image courtesy of Grossman/Kolpak)

Storing the sun's heat in chemical form -- rather than converting it to electricity or storing the heat itself in a heavily insulated container -- has significant advantages, since in principle the chemical material can be stored for long periods of time without losing any of its stored energy. The problem with that approach has been that until now the chemicals needed to perform this conversion and storage either degraded within a few cycles, or included the element ruthenium, which is rare and expensive.

Last year, MIT associate professor Jeffrey Grossman and four co-authors figured out exactly how fulvalene diruthenium -- known to scientists as the best chemical for reversibly storing solar energy, since it did not degrade -- was able to accomplish this feat. Grossman said at the time that better understanding this process could make it easier to search for other compounds, made of abundant and inexpensive materials, which could be used in the same way.

Now, he and postdoc Alexie Kolpak have succeeded in doing just that. A paper describing their new findings has just been published online in the journal Nano Letters, and will appear in print in a forthcoming issue.

The new material found by Grossman and Kolpak is made using carbon nanotubes, tiny tubular structures of pure carbon, in combination with a compound called azobenzene. The resulting molecules, produced using nanoscale templates to shape and constrain their physical structure, gain "new properties that aren't available" in the separate materials, says Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering.

Not only is this new chemical system less expensive than the earlier ruthenium-containing compound, but it also is vastly more efficient at storing energy in a given amount of space -- about 10,000 times higher in volumetric energy density, Kolpak says -- making its energy density comparable to lithium-ion batteries. By using nanofabrication methods, "you can control [the molecules'] interactions, increasing the amount of energy they can store and the length of time for which they can store it -- and most importantly, you can control both independently," she says.

Thermo-chemical storage of solar energy uses a molecule whose structure changes when exposed to sunlight, and can remain stable in that form indefinitely. Then, when nudged by a stimulus -- a catalyst, a small temperature change, a flash of light -- it can quickly snap back to its other form, releasing its stored energy in a burst of heat. Grossman describes it as creating a rechargeable heat battery with a long shelf life, like a conventional battery.



One of the great advantages of the new approach to harnessing solar energy, Grossman says, is that it simplifies the process by combining energy harvesting and storage into a single step. "You've got a material that both converts and stores energy," he says. "It's robust, it doesn't degrade, and it's cheap." One limitation, however, is that while this process is useful for heating applications, to produce electricity would require another conversion step, using thermoelectric devices or producing steam to run a generator.

While the new work shows the energy-storage capability of a specific type of molecule -- azobenzene-functionalized carbon nanotubes -- Grossman says the way the material was designed involves "a general concept that can be applied to many new materials." Many of these have already been synthesized by other researchers for different applications, and would simply need to have their properties fine-tuned for solar thermal storage.

The key to controlling solar thermal storage is an energy barrier separating the two stable states the molecule can adopt; the detailed understanding of that barrier was central to Grossman's earlier research on fulvalene dirunthenium, accounting for its long-term stability. Too low a barrier, and the molecule would return too easily to its "uncharged" state, failing to store energy for long periods; if the barrier were too high, it would not be able to easily release its energy when needed. "The barrier has to be optimized," Grossman says.

Already, the team is "very actively looking at a range of new materials," he says. While they have already identified the one very promising material described in this paper, he says, "I see this as the tip of the iceberg. We're pretty jazzed up about it."

Yosuke Kanai, assistant professor of chemistry at the University of North Carolina at Chapel Hill, says "the idea of reversibly storing solar energy in chemical bonds is gaining a lot of attention these days. The novelty of this work is how these authors have shown that the energy density can be significantly increased by using carbon nanotubes as nanoscale templates. This innovative idea also opens up an interesting avenue for tailoring already-known photoactive molecules for solar thermal fuels and storage in general."

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The Future of Metabolic Engineering: Designer Molecules, Cells and Microorganisms

The Future of Metabolic Engineering: Designer Molecules, Cells and Microorganisms

  5:22:00 PM    Science Lover

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Will we one day design and create molecules, cells and microorganisms that produce specific chemical products from simple, readily-available, inexpensive starting materials? Will the synthetic organic chemistry now used to produce pharmaceutical drugs, plastics and a host of other products eventually be surpassed by metabolic engineering as the mainstay of our chemical industries? Yes, according to Jay Keasling, chemical engineer and one of the world's foremost practitioners of metabolic engineering.

Metabolic engineering - the practice of 
altering genes and metabolic pathways 
within a cell or microorganism -- could 
one day be used to mass-produce biofuels, 
pharmaceuticals and other chemical 
products from inexpensive and renewable 
starting materials. (Credit: Flavio Robles, 
Berkeley Lab Public Affairs)

In a paper published in the journal Science Keasling discusses the potential of metabolic engineering -- one of the principal techniques of modern biotechnology -- for the microbial production of many of the chemicals that are currently derived from non-renewable resources or limited natural resources. Examples include, among a great many other possibilities, the replacement of gasoline and other transportation fuels with clean, green and renewable biofuels.

"Continued development of the tools of metabolic engineering will be necessary to expand the range of products that can be produced using biological systems, Keasling says. "However, when more of these tools are available, metabolic engineering should be just as powerful as synthetic organic chemistry, and together the two disciplines can greatly expand the number of chemical products available from renewable resources."

Keasling is the chief executive officer for the Joint BioEnergy Institute, a U.S. Department of Energy (DOE) bioenergy research center. He also holds joint appointments with the Lawrence Berkeley National Laboratory (Berkeley Lab), where he oversees that institute's biosciences research programs, and the University of California (UC), Berkeley, where he serves as director of the Synthetic Biology Engineering Research Center, and is the Hubbard Howe Jr. Distinguished Professor of Biochemical Engineering.

Metabolic engineering is the practice of altering genes and metabolic pathways within a cell or microorganism to increase its production of a specific substance. Keasling led one of the most successful efforts to date in the application of metabolic engineering, when he combined it with synthetic organic chemistry techniques to develop a microbial-based means of producing artemisinin, the most potent of all anti-malaria drugs. He and his research group at JBEI are now applying that same combination to the synthesis of liquid transportation fuels from lignocellulosic biomass. In all cases, the goal is to engineer microbes to perform as much of the chemistry required to produce a desired final product as possible.

"To date, microbial production of natural chemical products has been achieved by transferring product-specific enzymes or entire metabolic pathways from rare or genetically intractable organisms to those that can be readily engineered," Keasling says. "Production of non-natural specialty chemicals, bulk chemicals, and fuels has been enabled by combining enzymes or pathways from different hosts into a single microorganism, and by engineering enzymes to have new function."

These efforts have utilized well-known, industrial microorganisms, but future efforts, he says, may include designer molecules and cells that are tailor-made for the desired chemical and production process.

"In any future, metabolic engineering will soon rival and potentially eclipse synthetic organic chemistry," Keasling says.

Keasling cites the production of active pharmaceutical ingredients as one area where metabolic engineering enjoys a distinct advantage over synthetic organic chemistry. This includes three specific classes of chemicals -- alkaloids, which are primarily derived from plants; polyketides and non-ribosomal peptides, which are produced by various bacteria and fungi; and isoprenoids, which also are typically produced by microbes.

"Many of these natural products are too complex to be chemically synthesized and yet have a value that justifies the cost of developing a genetically engineered microorganism," Keasling says. "The cost of starting materials is generally a small fraction of the complete cost of these products, and relatively little starting material is necessary so availability is not an issue."

Keasling also says that metabolic engineering could provide a valuable alternative means of producing variations of terpenes, the hydrocarbon compounds common to the resins of conifers, in a form that could yield pharmaceuticals that are more effective for the treatment of human disease than the forms that nature has provided.

Perhaps the ripest targets of opportunity for future metabolic engineering efforts are petroleum-based bulk chemical products, including gasoline and other fuels, polymers and solvents. Because such products can be inexpensively catalyzed from petroleum, microbial production has until now been rare, but with fluctuating oil prices, dwindling resources and other considerations, the situation, Keasling says, has changed.

"It is now possible to consider production of these inexpensive bulk chemicals from low-cost starting materials, such as starch, sucrose, or cellulosic biomass with a microbial catalyst," he says. "The key to producing these bulk chemicals in metabolically-engineered cells will be our ability to make the exact molecule needed for existing products rather than something 'similar but green' that will require extensive product testing before it can be used."

In his Science paper, Keasling discusses the formidable roadblocks that stand in the way of a future in which microorganisms and molecules can be tailor-made through metabolic engineering, including the need for "debugging routines" that can find and fix errors in engineered cells. However, he is convinced these roadblocks can and will be overcome.

"One can even envision a day when cell manufacturing is done by different companies, each specializing in certain aspects of the synthesis, with one company constructing the chromosome, one company building the membrane and cell wall bag, and one company filling this bag with the basic molecules needed to boot up the cell."

The Joint BioEnergy Institute (JBEI) is one of three Bioenergy Research Centers funded by the U.S. Department of Energy to advance the development of the next generation of biofuels. It is a scientific partnership led by Berkeley Lab and including the Sandia National Laboratories, the University of California campuses of Berkeley and Davis, the Carnegie Institution for Science, and the Lawrence Livermore National Laboratory.

The Synthetic Biology Engineering Research Center (SynBERC) is a multi-institution partnership, funded by the National Science Foundation, that is aimed at "making biology easier to engineer." The SynBERC partnership is led by UC Berkeley and includes UC San Francisco, Harvard, MIT, Stanford, and Prairie View A&M University.

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Transparent Conductive Material Could Lead to Power-Generating Windows

Transparent Conductive Material Could Lead to Power-Generating Windows

  1:18:00 PM    Science Lover

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Scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Los Alamos National Laboratory have fabricated transparent thin films capable of absorbing light and generating electric charge over a relatively large area. The material, described in the journal Chemistry of Materials, could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity.

Top: Scanning electron microscopy image and zoom 
of conjugated polymer (PPV) honeycomb. Bottom 
(left-to-right): Confocal fluorescence lifetime images of 
conjugated honeycomb, of polymer/fullerene honeycomb 
double layer and of polymer/fullerene honeycomb blend. 
Efficient charge transfer within the whole framework is 
observed in the case of polymer/fullerene honeycomb 
blend as a dramatic reduction in the fluorescence lifetime. 
(Credit: Image courtesy of DOE/Brookhaven National 
Laboratory)

The material consists of a semiconducting polymer doped with carbon-rich fullerenes. Under carefully controlled conditions, the material self-assembles to form a reproducible pattern of micron-size hexagon-shaped cells over a relatively large area (up to several millimeters).

"Though such honeycomb-patterned thin films have previously been made using conventional polymers like polystyrene, this is the first report of such a material that blends semiconductors and fullerenes to absorb light and efficiently generate charge and charge separation," said lead scientist Mircea Cotlet, a physical chemist at Brookhaven's Center for Functional Nanomaterials (CFN).

Furthermore, the material remains largely transparent because the polymer chains pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers. "The densely packed edges strongly absorb light and may also facilitate conducting electricity," Cotlet explained, "while the centers do not absorb much light and are relatively transparent."

"Combining these traits and achieving large-scale patterning could enable a wide range of practical applications, such as energy-generating solar windows, transparent solar panels, and new kinds of optical displays," said co-author Zhihua Xu, a materials scientist at the CFN.

"Imagine a house with windows made of this kind of material, which, combined with a solar roof, would cut its electricity costs significantly. This is pretty exciting," Cotlet said.

The scientists fabricated the honeycomb thin films by creating a flow of micrometer-size water droplets across a thin layer of the polymer/fullerene blend solution. These water droplets self-assembled into large arrays within the polymer solution. As the solvent completely evaporates, the polymer forms a hexagonal honeycomb pattern over a large area.

"This is a cost-effective method, with potential to be scaled up from the laboratory to industrial-scale production," Xu said.

The scientists verified the uniformity of the honeycomb structure with various scanning probe and electron microscopy techniques, and tested the optical properties and charge generation at various parts of the honeycomb structure (edges, centers, and nodes where individual cells connect) using time-resolved confocal fluorescence microscopy.

The scientists also found that the degree of polymer packing was determined by the rate of solvent evaporation, which in turn determines the rate of charge transport through the material.

"The slower the solvent evaporates, the more tightly packed the polymer, and the better the charge transport," Cotlet said.

"Our work provides a deeper understanding of the optical properties of the honeycomb structure. The next step will be to use these honeycomb thin films to fabricate transparent and flexible organic solar cells and other devices," he said.

The research was supported at Los Alamos by the DOE Office of Science. The work was also carried out in part at the CFN and the Center for Integrated Nanotechnologies Gateway to Los Alamos facility. The Brookhaven team included Mircea Cotlet, Zhihua Xu, and Ranjith Krishna Pai. Collaborators from Los Alamos include Hsing-Lin Wang and Hsinhan Tsai, who are both users of the CFN facilities at Brookhaven, Andrew Dattelbaum from the Center for Integrated Nanotechnologies Gateway to Los Alamos facility, and project leader Andrew Shreve of the Materials Physics and Applications Division.

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