Tagged: Energy Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 7:15 pm on October 14, 2014 Permalink | Reply
    Tags: , Energy,   

    From ORNL: “New ORNL electric vehicle technology packs more punch in smaller package” 

    i1

    Oak Ridge National Laboratory

    Oct. 14, 2014
    Media Contact: Ron Walli
    Communications
    865.576.0226

    Using 3-D printing and novel semiconductors, researchers at the Department of Energy’s Oak Ridge National Laboratory have created a power inverter that could make electric vehicles lighter, more powerful and more efficient.

    At the core of this development is wide bandgap material made of silicon carbide with qualities superior to standard semiconductor materials. Power inverters convert direct current into the alternating current that powers the vehicle. The Oak Ridge inverter achieves much higher power density with a significant reduction in weight and volume.

    “Wide bandgap technology enables devices to perform more efficiently at a greater range of temperatures than conventional semiconductor materials,” said ORNL’s Madhu Chinthavali, who led the Power Electronics and Electric Machinery Group on this project. “This is especially useful in a power inverter, which is the heart of an electric vehicle.”

    Specific advantages of wide bandgap devices include: higher inherent reliability; higher overall efficiency; higher frequency operation; higher temperature capability and tolerance; lighter weight, enabling more compact systems; and higher power density.

    Additive manufacturing helped researchers explore complex geometries, increase power densities, and reduce weight and waste while building ORNL’s 30-kilowatt prototype inverter.

    thing
    ORNL’s 30-kilowatt power inverter offers greater reliability and power in a compact package.

    “With additive manufacturing, complexity is basically free, so any shape or grouping of shapes can be imagined and modeled for performance,” Chinthavali said. “We’re very excited about where we see this research headed.”

    Using additive manufacturing, researchers optimized the inverter’s heat sink, allowing for better heat transfer throughout the unit. This construction technique allowed them to place lower-temperature components close to the high-temperature devices, further reducing the electrical losses and reducing the volume and mass of the package.

    Another key to the success is a design that incorporates several small capacitors connected in parallel to ensure better cooling and lower cost compared to fewer, larger and more expensive “brick type” capacitors.

    The research group’s first prototype, a liquid-cooled all-silicon carbide traction drive inverter, features 50 percent printed parts. Initial evaluations confirmed an efficiency of nearly 99 percent, surpassing DOE’s power electronics target and setting the stage for building an inverter using entirely additive manufacturing techniques.

    Building on the success of this prototype, researchers are working on an inverter with an even greater percentage of 3-D printed parts that’s half the size of inverters in commercially available vehicles. Chinthavali, encouraged by the team’s results, envisions an inverter with four times the power density of their prototype.

    Others involved in this work, which was to be presented today at the Second Institute of Electrical and Electronics Engineers Workshop on Wide Bandgap Power Devices and Applications in Knoxville, were Curt Ayers, Steven Campbell, Randy Wiles and Burak Ozpineci.

    Research for this project was conducted at ORNL’s National Transportation Research Center and Manufacturing Demonstration Facility, DOE user facilities, with funding from DOE’s Office of Energy Efficiency and Renewable Energy.

    See the full article here.

    ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

    i2

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 8:57 pm on October 3, 2014 Permalink | Reply
    Tags: , Energy, , ,   

    From MIT: “Crumpled graphene could provide an unconventional energy storage” 


    MIT News

    October 3, 2014
    David L. Chandler | MIT News Office

    Two-dimensional carbon “paper” can form stretchable supercapacitors to power flexible electronic devices.

    When someone crumples a sheet of paper, that usually means it’s about to be thrown away. But researchers have now found that crumpling a piece of graphene “paper” — a material formed by bonding together layers of the two-dimensional form of carbon — can actually yield new properties that could be useful for creating extremely stretchable supercapacitors to store energy for flexible electronic devices.

    temp
    To form the crumpled graphene, a sheet of polymer material is stretched in both dimensions, then graphene paper is bonded to it. When the polymer is released in one direction, the graphene forms pleats, as shown in the bottom left image, taken with a scanning electron microscope (SEM). Then, when released in the other direction, it forms a chaotic crumpled pattern (top left). At top right, an SEM image shows the material in a partially crumpled state. At bottom right, SEM image of a piece that has been crumpled and then flattened out. Image courtesy of the researchers

    The finding is reported in the journal Scientific Reports by MIT’s Xuanhe Zhao, an assistant professor of mechanical engineering and civil and environmental engineering, and four other authors. The new, flexible supercapacitors should be easy and inexpensive to fabricate, the team says.

    “Many people are exploring graphene paper: It’s a good candidate for making supercapacitors, because of its large surface area per mass,” Zhao says. Now, he says, the development of flexible electronic devices, such as wearable or implantable biomedical sensors or monitoring devices, will require flexible power-storage systems.

    Like batteries, supercapacitors can store electrical energy, but they primarily do so electrostatically, rather than chemically — meaning they can deliver their energy faster than batteries can. Now Zhao and his team have demonstrated that by crumpling a sheet of graphene paper into a chaotic mass of folds, they can make a supercapacitor that can easily be bent, folded, or stretched to as much as 800 percent of its original size. The team has made a simple supercapacitor using this method as a proof of principle.

    The material can be crumpled and flattened up to 1,000 times, the team has demonstrated, without a significant loss of performance. “The graphene paper is pretty robust,” Zhao says, “and we can achieve very large deformations over multiple cycles.” Graphene, a structure of pure carbon just one atom thick with its carbon atoms arranged in a hexagonal array, is one of the strongest materials known.

    To make the crumpled graphene paper, a sheet of the material was placed in a mechanical device that first compressed it in one direction, creating a series of parallel folds or pleats, and then in the other direction, leading to a chaotic, rumpled surface. When stretched, the material’s folds simply smooth themselves out.

    Forming a capacitor requires two conductive layers — in this case, two sheets of crumpled graphene paper — with an insulating layer in between, which in this demonstration was made from a hydrogel material. Like the crumpled graphene, the hydrogel is highly deformable and stretchable, so the three layers remain in contact even while being flexed and pulled.

    Though this initial demonstration was specifically to make a supercapacitor, the same crumpling technique could be applied to other uses, Zhao says. For example, the crumpled graphene material might be used as one electrode in a flexible battery, or could be used to make a stretchable sensor for specific chemical or biological molecules.

    “This work is really exciting and amazing to me,” says Dan Li, a professor of materials engineering at Monash University in Australia who was not involved in this research. He says the team “provides an extremely simple but highly effective concept to make stretchable electrodes for supercapacitors by controlled crumpling of multilayered graphene films.” While other groups have made flexible supercapacitors, he says, “Making supercapacitors stretchable has been a great challenge. This paper provides a very smart way to tackle this challenge, which I believe will bring wearable energy storage devices closer.”

    The research team also included Jianfeng Zang at Huazhong University of Science and Technology and Changyang Cao, Yaying Feng, and Jie Liu at Duke University. The work was supported by the Office of Naval Research, the National Science Foundation, and the National 1000 Talents Program of China.

    See the full article here.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 4:29 pm on September 29, 2014 Permalink | Reply
    Tags: , , Energy, ,   

    From PPPL: “PPPL successfully tests system for mitigating instabilities called ‘ELMs’ “ 


    PPPL

    September 29, 2014
    John Greenwald

    PPPL has successfully tested a Laboratory-designed device to be used to diminish the size of instabilities known as “edge localized modes (ELMs)” on the DIII–D tokamak that General Atomics operates for the U.S. Department of Energy in San Diego. Such instabilities can damage the interior of fusion facilities.

    DIII-D
    DIII–D

    The PPPL device injects granular lithium particles into tokamak plasmas to increase the frequency of the ELMs. The method aims to make the ELMs smaller and reduce the amount of heat that strikes the divertor that exhausts heat in fusion facilities.

    The system could serve as a possible model for mitigating ELMs on ITER, the fusion facility under construction in France to demonstrate the feasibility of fusion energy.

    iter tok
    ITER Tokamak

    “ELMs are a big issue for ITER,” said Mickey Wade, director of the DIII-D national fusion program at General Atomics. Large-scale ELMs, he noted, could melt plasma-facing components inside the ITER tokamak.

    General Atomics plans to install the PPPL-designed device, developed by physicist Dennis Mansfield and engineer Lane Roquemore, on DIII-D this fall. Previous experiments using deuterium-injection rather than lithium-injection have demonstrated the ability to increase the ELMs frequency on DIII-D, the ASDEX-Upgrade in Germany and the Joint European Torus in the United Kingdom.

    jet
    Joint European Torus

    Researchers at DIII-D now want to see how the results for lithium-injection compare with those obtained in the deuterium experiments on the San Diego facility. “We want to put them side-by-side,” Wade said.

    PPPL-designed systems have proven successful in mitigating ELMs on the EAST tokamak in Hefei, China, and have been used on a facility operated by the Italian National Agency for New Technologies in Frascati, Italy. A system also is planned for PPPL’s National Spherical Torus Experiment (NSTX), the Laboratory’s major fusion experiment, which is undergoing a $94 million upgrade.

    PPPL NSTX
    PPPL NSTX

    PPPL used salt grain-sized plastic pellets as proxies for lithium granules in testing the system for DIII-D. The pellets fell through a pinhole-sized opening inside a dropper to a rotating high-speed propeller that projected them onto a target precisely as planned.

    Joining Mansfield and Roquemore for the tests were physicists Erik Gilson and Alessandro Bortolon, a former University of Tennessee researcher now at PPPL who will begin an assignment to the DIII-D tokamak at General Atomics this fall. Also participating were Rajesh Maingi, the head of research on edge physics and plasma-facing components at PPPL, and engineer Alexander Nagy, who is on assignment to DIII-D.

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 4:04 pm on September 29, 2014 Permalink | Reply
    Tags: , , Energy,   

    From LBL: “MaxBin: Automated Sorting Through Metagenomes” 

    Berkeley Logo

    Berkeley Lab

    September 29, 2014
    Lynn Yarris (510) 486-5375

    Microbes – the single-celled organisms that dominate every ecosystem on Earth – have an amazing ability to feed on plant biomass and convert it into other chemical products. Tapping into this talent has the potential to revolutionize energy, medicine, environmental remediation and many other fields. The success of this effort hinges in part on metagenomics, the emerging technology that enables researchers to read all the individual genomes of a sample microbial community at once. However, given that even a teaspoon of soil can contain billions of microbes, there is a great need to be able to cull the genomes of individual microbial species from a metagenomic sequence.

    Enter MaxBin, an automated software program for binning (sorting) the genomes of individual microbial species from metagenomic sequences. Developed at the U.S. Department of Energy (DOE)’s Joint BioEnergy Institute (JBEI), under the leadership of Steve Singer, who directs JBEI’s Microbial Communities Group, MaxBin facilitates the genomic analysis of uncultivated microbial populations that can hold the key to the production of new chemical materials, such as advanced biofuels or pharmaceutical drugs.

    cd
    MaxBin, an automated software program for binning the genomes of individual microbial species from metagenomic sequences, is available on-line through JBEI.

    “MaxBin automates the binning of assembled metagenomic scaffolds using an expectation-maximization algorithm after the assembly of metagenomic sequencing reads,” says Singer, a chemist who also holds an appointment with Berkeley Lab’s Earth Sciences Division. “Previous binning methods either required a significant amount of work by the user, or required a large number of samples for comparison. MaxBin requires only a single sample and is a push-button operation for users.”

    three
    JBEI researchers Yu-Wei Wu, Steve Singer and Danny Tang developed MaxBin to automatically recover individual genomes from metagenomes using an expectation-maximization algorithm. (Photo by Roy Kaltschmidt)

    The key to the success of MaxBin is its expectation-maximization algorithm, which was developed by Yu-Wei Wu, a post-doctoral researcher in Singer’s group. This algorithm enables the classification of metagenomic sequences into discrete bins that represent the genomes of individual microbial populations within a sample community.

    “Using our expectation-maximization algorithm, MaxBin combines information from tetranucleotide frequencies and scaffold coverage levels to organize metagenomic sequences into the individual bins, which are predicted from an initial identification of marker genes in assembled sequences,” Wu says.

    MaxBin was successfully tested on samples from the Human Microbiome Project and from green waste compost. In these tests, which were carried out by Yung-Tsu Tang, a student intern from the City College of San Francisco, MaxBin proved to be highly accurate in its ability to recover individual genomes from metagenomic datasets with variable sequencing coverages.

    “Applying MaxBin to an enriched cellulolytic consortia enabled us to identify a number of uncultivated cellulolytic bacteria, including a myxobacterium that possesses a remarkably reduced genome and expanded set of genes for biomass deconstruction compared to its closest sequenced relatives,” Singer says. “This demonstrates that the processes required for recovering genomes from metagenomic datasets can be applied to understanding biomass breakdown in the environment”.

    MaxBin is now being used at JBEI in its efforts to use microbes for the production of advanced biofuels – gasoline, diesel and jet fuel – from plant biomass. MaxBin is also available for downloading. To date, more than 150 researchers have accessed it.

    A paper describing MaxBin in detail has been published in the journal Microbiome. The paper is titled MaxBin: an automated binning method to recover individual genomes from metagenomes using an expectation-maximization algorithm. Co-authoring this paper in addition to Singer, Wu and Tang, were Susannah Tringe of the Joint Genome Institute, and Blake Simmons of JBEI.

    • See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

    University of California Seal

    DOE Seal

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 1:59 pm on September 26, 2014 Permalink | Reply
    Tags: , , Energy,   

    From PNNL: “Off-shore Power Potential Floating in the Wind” 


    PNNL Lab

    September 2014
    Web Publishing Services

    Results
    : Two bright yellow buoys – each worth $1.3 million – are being deployed by Pacific Northwest National Laboratory in Washington State’s Sequim Bay. The massive, 20,000-pound buoys are decked out with the latest in meteorological and oceanographic equipment to enable more accurate predictions of the power-producing potential of winds that blow off U.S. shores. Starting in November, they will be commissioned for up to a year at two offshore wind demonstration projects: one near Coos Bay, Oregon, and another near Virginia Beach, Virginia.

    off
    PNNL staff conduct tests in Sequim Bay, Washington, while aboard one of two new research buoys being commissioned to more accurately predict offshore wind’s power-producing potential.

    “We know offshore winds are powerful, but these buoys will allow us to better understand exactly how strong they really are at the heights of wind turbines,” said PNNL atmospheric scientist Dr. William J. Shaw. “Data provided by the buoys will give us a much clearer picture of how much power can be generated at specific sites along the American coastline – and enable us to generate that clean, renewable power sooner.”

    Why It Matters: Offshore wind is a new frontier for U.S. renewable energy developers. There’s tremendous power-producing potential, but limited information is available about ocean-based wind resources. A recent report estimated the U.S. could power nearly 17 million homes by generating more than 54 gigawatts of offshore wind energy, but more information is needed.

    See the full article here.

    Pacific Northwest National Laboratory (PNNL) is one of the United States Department of Energy National Laboratories, managed by the Department of Energy’s Office of Science. The main campus of the laboratory is in Richland, Washington.

    PNNL scientists conduct basic and applied research and development to strengthen U.S. scientific foundations for fundamental research and innovation; prevent and counter acts of terrorism through applied research in information analysis, cyber security, and the nonproliferation of weapons of mass destruction; increase the U.S. energy capacity and reduce dependence on imported oil; and reduce the effects of human activity on the environment. PNNL has been operated by Battelle Memorial Institute since 1965.

    i1

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 8:14 pm on September 21, 2014 Permalink | Reply
    Tags: , , Energy,   

    From M.I.T.: “Magnetic fields make the excitons go ’round” 


    MIT News

    September 21, 2014
    David L. Chandler | MIT News Office

    A major limitation in the performance of solar cells happens within the photovoltaic material itself: When photons strike the molecules of a solar cell, they transfer their energy, producing quasi-particles called excitons — an energized state of molecules. That energized state can hop from one molecule to the next until it’s transferred to electrons in a wire, which can light up a bulb or turn a motor.

    temp

    But as the excitons hop through the material, they are prone to getting stuck in minuscule defects, or traps — causing them to release their energy as wasted light.

    Now a team of researchers at MIT and Harvard University has found a way of rendering excitons immune to these traps, possibly improving photovoltaic devices’ efficiency. The work is described in a paper in the journal Nature Materials.

    Their approach is based on recent research on exotic electronic states known as topological insulators, in which the bulk of a material is an electrical insulator — that is, it does not allow electrons to move freely — while its surface is a good conductor.

    The MIT-Harvard team used this underlying principle, called topological protection, but applied it to excitons instead of electrons, explains lead author Joel Yuen, a postdoc in MIT’s Center for Excitonics, part of the Research Laboratory of Electronics. Topological protection, he says, “has been a very popular idea in the physics and materials communities in the last few years,” and has been successfully applied to both electronic and photonic materials.

    Moving on the surface

    Topological excitons would move only at the surface of a material, Yuen explains, with the direction of their motion determined by the direction of an applied magnetic field. In that respect, their behavior is similar to that of topological electrons or photons.

    In its theoretical analysis, the team studied the behavior of excitons in an organic material, a porphyrin thin film, and determined that their motion through the material would be immune to the kind of defects that tend to trap excitons in conventional solar cells.

    The choice of porphyrin for this analysis was based on the fact that it is a well-known and widely studied family of materials, says co-author Semion Saikin, a postdoc at Harvard and an affiliate of the Center for Excitonics. The next step, he says, will be to extend the analysis to other kinds of materials.

    por
    Structure of porphine, the simplest porphyrin

    While the work so far has been theoretical, experimentalists are eager to pursue the concept. Ultimately, this approach could lead to novel circuits that are similar to electronic devices but based on controlling the flow of excitons rather that electrons, Yuen says. “If there are ever excitonic circuits,” he says, “this could be the mechanism” that governs their functioning. But the likely first application of the work would be in creating solar cells that are less vulnerable to the trapping of excitons.

    Eric Bittner, a professor of chemistry at the University of Houston who was not associated with this work, says, “The work is interesting on both the fundamental and practical levels. On the fundamental side, it is intriguing that one may be able to create excitonic materials with topological properties. This opens a new avenue for both theoretical and experimental work. … On the practical side, the interesting properties of these materials and the fact that we’re talking about pretty simple starting components — porphyrin thin films — makes them novel materials for new devices.”

    The work received support from the U.S. Department of Energy and the Defense Threat Reduction Agency. Norman Yao, a graduate student at Harvard, was also a co-author.

    See the full article here.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 7:53 pm on September 21, 2014 Permalink | Reply
    Tags: , , Energy,   

    From M.I.T.: “New formulation leads to improved liquid battery” 


    MIT News

    September 21, 2014
    David L. Chandler | MIT News Office

    Cheaper, longer-lasting materials could enable batteries that make wind and solar energy more competitive.

    temp

    Researchers at MIT have improved a proposed liquid battery system that could enable renewable energy sources to compete with conventional power plants.

    Donald Sadoway and colleagues have already started a company to produce electrical-grid-scale liquid batteries, whose layers of molten material automatically separate due to their differing densities. But the new formula — published in the journal Nature by Sadoway, former postdocs Kangli Wang and Kai Jiang, and seven others — substitutes different metals for the molten layers used in a battery previously developed by the team.

    Sadoway, the John F. Elliott Professor of Materials Chemistry, says the new formula allows the battery to work at a temperature more than 200 degrees Celsius lower than the previous formulation. In addition to the lower operating temperature, which should simplify the battery’s design and extend its working life, the new formulation will be less expensive to make, he says.

    The battery uses two layers of molten metal, separated by a layer of molten salt that acts as the battery’s electrolyte (the layer that charged particles pass through as the battery is charged or discharged). Because each of the three materials has a different density, they naturally separate into layers, like oil floating on water.

    The original system, using magnesium for one of the battery’s electrodes and antimony for the other, required an operating temperature of 700 C. But with the new formulation, with one electrode made of lithium and the other a mixture of lead and antimony, the battery can operate at temperatures of 450 to 500 C.

    Extensive testing has shown that even after 10 years of daily charging and discharging, the system should retain about 85 percent of its initial efficiency — a key factor in making such a technology an attractive investment for electric utilities.

    Currently, the only widely used system for utility-scale storage of electricity is pumped hydro, in which water is pumped uphill to a storage reservoir when excess power is available, and then flows back down through a turbine to generate power when it is needed. Such systems can be used to match the intermittent production of power from irregular sources, such as wind and solar power, with variations in demand. Because of inevitable losses from the friction in pumps and turbines, such systems return about 70 percent of the power that is put into them (which is called the “round-trip efficiency”).

    Sadoway says his team’s new liquid-battery system can already deliver the same 70 percent efficiency, and with further refinements may be able to do better. And unlike pumped hydro systems — which are only feasible in locations with sufficient water and an available hillside — the liquid batteries could be built virtually anywhere, and at virtually any size. “The fact that we don’t need a mountain, and we don’t need lots of water, could give us a decisive advantage,” Sadoway says.

    The biggest surprise for the researchers was that the antimony-lead electrode performed so well. They found that while antimony could produce a high operating voltage, and lead gave a low melting point, a mixture of the two combined both advantages, with a voltage as high as antimony alone, and a melting point between that of the two constituents — contrary to expectations that lowering the melting point would come at the expense of also reducing the voltage.

    “We hoped [the characteristics of the two metals] would be nonlinear,” Sadoway says — that is, that the operating voltage would not end up halfway between that of the two individual metals. “They proved to be [nonlinear], but beyond our imagination. There was no decline in the voltage. That was a stunner for us.”

    Not only did that provide significantly improved materials for the group’s battery system, but it opens up whole new avenues of research, Sadoway says. Going forward, the team will continue to search for other combinations of metals that might provide even lower-temperature, lower-cost, and higher-performance systems. “Now we understand that liquid metals bond in ways that we didn’t understand before,” he says.

    With this fortuitous finding, Sadoway says, “Nature tapped us on the shoulder and said, ‘You know, there’s a better way!’” And because there has been little commercial interest in exploring the properties and potential uses of liquid metals and alloys of the type that are most attractive as electrodes for liquid metal batteries, he says, “I think there’s still room for major discoveries in this field.”

    Robert Metcalfe, professor of innovation at the University of Texas at Austin, who was not involved in this work, says, “The Internet gave us cheap and clean connectivity using many kinds of digital storage. Similarly, we will solve cheap and clean energy with many kinds of storage. Energy storage will absorb the increasing randomness of energy supply and demand, shaving peaks, increasing availability, improving efficiency, lowering costs.”

    Metcalfe adds that Sadoway’s approach to storage using liquid metals “is very promising.”

    The research was supported by the U.S. Department of Energy’s Advanced Research Projects Agency-Energy and by French energy company Total.

    See the full article here.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 1:46 pm on August 26, 2014 Permalink | Reply
    Tags: , Energy, , , ,   

    From Berkeley Lab: “Competition for Graphene” 

    Berkeley Logo

    Berkeley Lab

    August 26, 2014
    Lynn Yarris (510) 486-5375

    A new argument has just been added to the growing case for graphene being bumped off its pedestal as the next big thing in the high-tech world by the two-dimensional semiconductors known as MX2 materials. An international collaboration of researchers led by a scientist with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has reported the first experimental observation of ultrafast charge transfer in photo-excited MX2 materials. The recorded charge transfer time clocked in at under 50 femtoseconds, comparable to the fastest times recorded for organic photovoltaics.

    “We’ve demonstrated, for the first time, efficient charge transfer in MX2 heterostructures through combined photoluminescence mapping and transient absorption measurements,” says Feng Wang, a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and the University of California (UC) Berkeley’s Physics Department. “Having quantitatively determined charge transfer time to be less than 50 femtoseconds, our study suggests that MX2 heterostructures, with their remarkable electrical and optical properties and the rapid development of large-area synthesis, hold great promise for future photonic and optoelectronic applications.”

    fw
    Feng Wang is a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Physics Department. (Photo by Roy Kaltschmidt)

    Wang is the corresponding author of a paper in Nature Nanotechnology describing this research. The paper is titled Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures. Co-authors are Xiaoping Hong, Jonghwan Kim, Su-Fei Shi, Yu Zhang, Chenhao Jin, Yinghui Sun, Sefaattin Tongay, Junqiao Wu and Yanfeng Zhang.

    MX2 monolayers consist of a single layer of transition metal atoms, such as molybdenum (Mo) or tungsten (W), sandwiched between two layers of chalcogen atoms, such as sulfur (S). The resulting heterostructure is bound by the relatively weak intermolecular attraction known as the van der Waals force. These 2D semiconductors feature the same hexagonal “honeycombed” structure as graphene and superfast electrical conductance, but, unlike graphene, they have natural energy band-gaps. This facilitates their application in transistors and other electronic devices because, unlike graphene, their electrical conductance can be switched off.

    “Combining different MX2 layers together allows one to control their physical properties,” says Wang, who is also an investigator with the Kavli Energy NanoSciences Institute (Kavli-ENSI). “For example, the combination of MoS2 and WS2 forms a type-II semiconductor that enables fast charge separation. The separation of photoexcited electrons and holes is essential for driving an electrical current in a photodetector or solar cell.”

    In demonstrating the ultrafast charge separation capabilities of atomically thin samples of MoS2/WS2 heterostructures, Wang and his collaborators have opened up potentially rich new avenues, not only for photonics and optoelectronics, but also for photovoltaics.

    photo
    Photoluminescence mapping of a MoS2/WS2 heterostructure with the color scale representing photoluminescence intensity shows strong quenching of the MoS2 photoluminescence. (Image courtesy of Feng Wang group)

    “MX2 semiconductors have extremely strong optical absorption properties and compared with organic photovoltaic materials, have a crystalline structure and better electrical transport properties,” Wang says. “Factor in a femtosecond charge transfer rate and MX2 semiconductors provide an ideal way to spatially separate electrons and holes for electrical collection and utilization.”

    Wang and his colleagues are studying the microscopic origins of charge transfer in MX2 heterostructures and the variation in charge transfer rates between different MX2 materials.

    “We’re also interested in controlling the charge transfer process with external electrical fields as a means of utilizing MX2 heterostructures in photovoltaic devices,” Wang says.

    This research was supported by an Early Career Research Award from the DOE Office of Science through UC Berkeley, and by funding agencies in China through the Peking University in Beijing.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

    University of California Seal

    DOE Seal

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
    Lenovo

    Dell
    Dell

     
  • richardmitnick 1:38 pm on July 28, 2014 Permalink | Reply
    Tags: , Energy, ,   

    From Berkeley Lab: “Cagey Material Acts as Alcohol Factory” 

    Berkeley Logo

    Berkeley Lab

    July 28, 2014
    Kate Greene

    Some chemical conversions are harder than others. Refining natural gas into an easy-to-transport, easy-to-store liquid alcohol has so far been a logistic and economic challenge. But now, a new material, designed and patented by researchers at Lawrence Berkeley National Laboratory (Berkeley Lab), is making this process a little easier. The research, published earlier this year in Nature Chemistry, could pave the way for the adoption of cheaper, cleaner-burning fuels.

    “Hydrocarbons like ethane and methane could be used as fuel, but they’re hard to store and transport because they’re gases,” says Dianne Xiao, graduate student at the University of California Berkeley. “But if you have a catalyst that can selectively turn them into alcohols, which are much easier to transfer and store,” she says. “that would make things a lot easier.”

    Xiao and Jeffrey Long, scientist in Berkeley Lab’s Materials Sciences Division and professor of chemistry at the UC Berkeley focused this project on converting ethane to ethanol.

    two
    Jeff Long, Materials Sciences scientist, with student Dianne Xiao. The team’s research enabled MOFs to oxidize ethane to ethanol. Credit: Roy Kaltschmidt

    Ethanol is a potential alternative fuel that burns cleaner and has a higher energy density than other alternative fuels like methanol. One problem with ethanol, however, is that current methods for production require extreme heat, which makes it expensive.

    The innovation came when Long and Xiao designed a material called Fe-MOF-74, in a class of materials called metal-organic frameworks or MOFs. Because of their cage-shaped structures, MOFs boast a high surface area, which mean they can absorb extremely large amounts of gas or liquid compared to the weight of the MOF itself.

    Since MOFs are essentially structured like a collection of tiny cages, they can capture other molecules, acting as a filter. Additionally, they can perform chemistry as molecules pass through the cages, becoming little chemical factories that convert one substance to another.

    It’s this chemical-conversion feature of MOFs that Long and Xiao took advantage of. Ethane is a molecule made of two carbon atoms where each atom is surrounded by atoms of hydrogen. Ethanol is also made of two carbon atoms bonded to hydrogen atoms, but one of its carbon atoms is also bonded to a hydrogen-oxygen ion called a hydroxyl.

    hex
    A view inside the MOF: hexagonal channels lined with iron. Credit: Dianne Xiao, Berkeley

    Previous attempts to add a hydroxyl ion to ethane to make ethanol have required high pressure and high temperatures that range from 200 to 300 degrees Celsius. It’s costly and inconvenient.

    But by using a specially designed MOF—one in which a kind of iron was added inside the tiny molecular cages—the researchers were able to reduce the need for extreme heat, converting ethane to alcohol at just 75 degrees Celsius.

    “This is getting toward a holy grail in chemistry which is to be able to cleanly take alkanes to alcohols without a lot of energy,” says Long. Long and Xiao worked closely with researchers at the National Institute of Standards and Technology, the University of Minnesota, the University of Delaware, and the University of Turin to design, model, and characterize the MOF and resultant ethanol production.

    Next steps involve tweaking the concentrations of iron in the MOF to produce a more efficient conversion, says Xiao. “It’s a promising proof of principle,” she says. “It’s exciting that we can do this now at low temperature and low pressures.”

    This research was funded by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. Reactivity studies were supported by the Laboratory Directed Research and Development Program of Lawrence Berkeley National Laboratory. Work at the Molecular Foundry and experiments performed at the Advanced Light Source were funded by the DOE’s Office of Basic Energy Sciences.

    A U.S. Department of Energy National Laboratory Operated by the University of California

    University of California Seal

    DOE Seal


    ScienceSprings is powered by MAINGEAR computers

     
  • richardmitnick 6:11 am on July 22, 2014 Permalink | Reply
    Tags: , , Energy,   

    From ESO: “Solar Farm to be Installed at La Silla” 


    European Southern Observatory

    21 July 2014
    Roberto Tamai
    E-ELT Programme Manager
    Garching bei München, Germany
    Tel: +49 89 3200 6367
    Email: rtamai@eso.org

    Lars Lindberg Christensen
    Head of ESO ePOD
    ESO ePOD, Garching, Germany
    Tel: +49 89 3200 6761
    Cellular: +49 173 3872 621
    E-mail: lars@eso.org

    As part of its green initiatives, ESO has signed an agreement with the Chilean company, Astronomy and Energy (a subsidiary of the Spanish LKS Group), to install a solar farm at the La Silla Observatory. ESO has been working on green solutions for supplying energy to its sites for several years, and these are now coming to fruition. Looking to the future, renewables are considered vital to satisfy energy needs in a sustainable manner.

    ESO LaSilla
    ESO at LaSilla

    solar

    ESO’s ambitious programme is focused on achieving the highest quality of astronomical research. This requires the design, construction and operation of the most powerful ground-based observing facilities in the world. However, the operations at ESO’s observatories present significant challenges in terms of their energy usage.

    Despite the abundance of sunshine at the ESO sites, it has not been possible up to now to make efficient use of this natural source of power. Astronomy and Energy will supply a means of effectively exploiting solar energy using crystalline photovoltaic modules (solar panels), which will be installed at La Silla.

    The installation will cover an area of more than 100 000 square metres, with the aim of being ready to supply the site by end of the year.

    The global landscape for energy has changed considerably over the last 20 years. As energy prices are increasing and vary unpredictably, ESO has been keen to look into ways to control its energy costs and also limit its ecological impact. The organisation has already managed to successfully reduce its power consumption at La Silla, and despite the additions of the VISTA and VST survey telescopes, power use has remained stable over the past few years at the Paranal Observatory, site of the VLT.

    ESO Vista Telescope
    ESO VISTA Telescope

    ESO VST telescope
    ESO VST Telescope

    The much-improved efficiency of solar cells has meant they have become a viable alternative to exploit solar energy. Solar cells of the latest generation are considered to be very reliable and almost maintenance-free, characteristics that contribute to a high availability of electric power, as required at astronomical observatories.

    As ESO looks to the future, it seeks further sustainable energy sources to be compatible across all its sites, including Cerro Armazones — close to Cerro Paranal and the site of the future European Extremely Large Telescope (E-ELT). This goal will be pursued not only by installing primary sources of renewable energy, as at La Silla, but also by realising connections to the Chilean interconnected power systems, where non-conventional renewable energy sources are going to constitute an ever-growing share of the power and energy mixes.

    The installation of a solar farm at La Silla is one of a series of initiatives ESO is taking to tackle the environmental impacts of its operations, as can be viewed here. Green energy is strongly supported by the Chilean government, which aims to increase the Chilean green energy share to 25% in 2020, with a possible target of 30% by 2030.

    See the full article, with note, here.

    Visit ESO in Social Media-

    Facebook

    Twitter

    YouTube

    ESO Main

    ESO, European Southern Observatory, builds and operates a suite of the world’s most advanced ground-based astronomical telescopes.


    ScienceSprings is powered by MAINGEAR computers

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
Follow

Get every new post delivered to your Inbox.

Join 342 other followers

%d bloggers like this: