How you remove the “dust” from hundreds of acres of Solar Panels? (Video)
The No Water, Mechanical, Automated, Dusting Device for photovoltaic installations (NOMADD) effectively removes dust without requiring any water or labor. This environmentally friendly technology enables more widespread use of solar photovoltaics in arid regions and helps to conserve the Earth’s water resources and harness the full potential of solar energy.
This technology is part of KAUST’s technology commercialization program that seeks to stimulate development and commercial use of KAUST-developed technologies. For more information, contact us at IP@kaust.edu.sa.
27 Aug 2014
JQI (Joint Quantum Institute) Fellow Jay Sau, in collaboration with physicists from Harvard and Yale, has been studying the effects of embedding magnetic spins onto the surface of a superconductor. They recently report in paper that was chosen as an “Editor’s Suggestion” in Physical Review Letters, that the spins can interact differently than previously thought. This hybrid platform could be useful for quantum simulations of complex spin systems, having the special feature that the interactions may be controllable, something quite unusual for most condensed matter systems.
The textbook quantum system known as a spin can be realized in different physical platforms. Due to advances in fabrication and imaging, magnetic impurities embedded onto a substrate have emerged as an exciting prospect for studying spin physics. Quantum ‘spin’ is related to a particle’s intrinsic angular momentum. What’s neat is that while the concept is fairly abstract, numerous effects in nature, such as magnetism, map onto mathematical spin models.
A single spin is useful, but most practical applications and studies of complex phenomena require controlling many interacting spins. By themselves, spins will interact with each other, with the interaction strength vanishing as spins are separated. In experiments, physicists will often use techniques, such as lasers and/or magnetic fields, to control and modify the interplay between spins. While possible in atomic systems, controlling interactions between quantum spins has not been straightforward or even possible in most solid state systems.
In principle, the best way to enhance communication between spins in materials is to use the moving electrons as intermediaries. Mobile electrons are easy to come by in conductors, but from a quantum physics perspective, these materials are dirty and noisy. Here, electrons flow around, scattering from the countless numbers of vibrating atoms, creating disruptions and masking quantum effects. One way physicists get around this obstacle is to place the spins on a superconducting substrate, which happens to be a quiet, pristine quantum environment.
Why are superconductors are a clean quantum host for spins? To answer this, consider the band structure of this system.
Band structure describes the behavior of electrons in solids. Inside isolated atoms, electrons possess only certain discrete energies separated by forbidden regions. In a solid, atoms are arranged in a repeating pattern, called a lattice. Due to the atoms’ close proximity, their accompanying electrons are effectively shared. The equivalent energy level diagram for the collective arrangement of atoms in a solid consists not of discrete levels, but of bunches or bands of levels representing nearly a continuum of energy values. In a solid, electrons normally occupy the lowest lying energy levels. In conducting solids the next higher energy level (above the highest filled level) is close enough in energy that transitions are allowed, facilitating flow of electrons in the form of a current.
Where do superconductors, in which electrical current flows freely without dissipation, fit into this energy level scheme? This effect is not the result of perfectly closing a gap–in fact the emergence of zero resistivity is a phase transition. As some materials are cooled the electrons can begin to interact, even over large distances, through vibrations in the crystal called phonons. This is called “Cooper pairing.” The pairs, though relatively weak, require some amount of energy to break, which translates into a gap in the band structure forming between the lowest energy superconducting state and the higher energy, non-superconducting states. In some sense, the superconducting state is a quantum environment that is isolated from the noise of the normal conducting state.
In this research, physicists consider what happens to the spin-spin interactions when the spins are embedded onto a superconductor. Generally, when the spins are separated by an amount greater than what’s called the coherence length, they are known to weakly interact antiferromagnetically (spin orientation alternating). It turns out that when the spins are closer together, their interactions are more complex than previously thought, and have the potential to be tunable. The research team corrects existing textbook theory that says that the spin-spin interactions oscillate between ferromagnetic (all spins having the same orientation) and antiferromagnetic. This type of interaction (called RKKY) is valid for regular conductors, but is not when the substrate is a superconductor.
What’s happening here is that, similar to semiconductors, the magnetic spin impurities are affecting the band structure. The spins induce what are called Shiba states, which are allowed electron energy levels in the superconducting gap. This means that there is a way for superconducting electron pairs to break-up and occupy higher, non-superconducting energy states. For this work, the key point is that when two closely-spaced spins are anti-aligned then their electron Shiba states mix together to strengthen their effective antiferromagnetic spin interaction. An exciting feature of this result is that the amount of mixing, and thus effective interaction strength, can be tuned by shifting around the relative energy of Shiba states within the gapped region. The team finds that when Shiba states are in the middle of the superconducting gap, the antiferromagnetic interaction between spins dominates.
Author and theorist Jay Sau explains the promise of this platform, “What this spin-superconductor system provides is the ability connect many quantum systems together with a definitive interaction. Here you can potentially put lots of impurity atoms in a small region of superconductor and they will all interact antiferromagnetically. This is the ideal situation for forming exotic spin states.”
Arrays of spins with controllable interactions are hard to come by in the laboratory and, when combined with the ability to image single spin impurities via scanning tunneling microscopy (STM), this hybrid platform may open new possibilities for studying complex interacting quantum phenomena.
From Sau’s perspective, “We are at the stage where our understanding of quantum many-body things is so bad that we don’t necessarily even want to target simulating a specific material. If we just start to get more examples of complicated quantum systems that we understand, then we have already made progress.”
– See more at: http://jqi.umd.edu/news/sprinkling-spin-physics-onto-
A new $AUD30 million research facility at RMIT University in Melbourne, Australia, will drive cutting-edge advances in micro- and nano-technologies.
The MicroNano Research Facility (MNRF) will bring to Australia the world’s first rapid 3D nanoscale printer and will support projects that span across the traditional disciplines of physics, chemistry, engineering, biology and medicine.
The City campus facility will be launched by Vice-Chancellor and President, Professor Margaret Gardner AO, on Wednesday, 27 August.
Professor Gardner said the opening of the state-of-the-art laboratories and clean rooms was the start of an exciting new chapter in cross-disciplinary nano research.
“At the heart of the MicroNano Research Facility’s mission is bringing together disparate disciplines to enable internationally-leading research activity,” she said.
“RMIT has long been a pioneer in this field, opening Australia’s first academic clean rooms at the Microelectronics and Materials Technology Centre in 1983.
“Over three decades later, this investment in the world-class MNRF will enable RMIT’s leading researchers to continue to break new ground and transform the future.”
Among the equipment available to researchers in the 1200 square metre facility will be the world’s first rapid 3D nanoscale printer, capable of producing thousands of structures – each a fraction of the width of a human hair – in seconds.
Designed by architects SKM Jacobs, the MNRF also offers researchers access to more than 50 cutting-edge tools, including focused ion beam lithography with helium, neon, and gallium ion beams to enable imaging and machining objects to 0.5 nm resolution – about 5 to 10 atoms.
Director of the MNRF, Professor James Friend, said 10 research teams would work at the new facility on a broad range of projects, including:
- building miniaturised motors – or microactuators – to retrieve blood clots from deep within the brain, enabling minimally invasive neurological intervention in people affected by strokes or aneurysms;
- improving drug delivery via the lungs through new techniques that can atomise large biomolecules – including drugs, DNA, antibodies and even cells – into tiny droplets to avoid the damage of conventional nebulisation;
- developing innovative energy harvesting techniques that change the way batteries are recharged, using novel materials that can draw on the energy generated simply by people walking around; and,
- inventing ways to use water to remove toxins from fabric dyes, with new nanotechnologies that can facilitate the breaking down of those dyes with nanostructured catalysts.
“This facility is all about ensuring researchers have the freedom to imagine and safely realise the impossible at tiny scales and beyond,” Professor Friend said.
“Having access to purpose-designed laboratories and leading-edge equipment opens tremendous opportunities for RMIT and for those we collaborate with, enabling us to advance the development of truly smart technology solutions to some of our most complex problems.”
Laboratories in the MNRF will include:
- Gas sensors laboratory
- Metrology laboratory
- Novel Fabrication laboratory
- PC2 mammalian cell laboratory
- Photolithography laboratory
- Physical vapour deposition laboratory
- Polydimethylsiloxane (PDMS) and nanoparticle laboratory
- Wet etch laboratory
- Support laboratory
The MNRF will be a key enabler of RMIT’s flagship Health Innovations Research Institute and Platform Technologies Research Institute.
A unique teaching facility will also be affiliated with the MNRF.
The Micro Nano Teaching Facility (MNTF) is the first of its kind in Australia, enabling undergraduate and postgraduate engineering student trainees to study clean room operations and micro-fabrication
“According to an article in ASME.org, nanotechnology “will leave virtually no aspect of life untouched and is expected to be in widespread use by 2020.” In addition, a policy paper by the National Academy of Agricultural Sciences (NAAS) describes nanotechnology as modern history’s “sixth revolutionary technology,” following the industrial revolution in the mid-1700s, nuclear energy revolution in the 1940s, green revolution in the 1960s, information technology revolution in the 1980s, and biotechnology revolution in the 1990s.”
Genesis Nanotechnology – “Nanotechnology will change the way we innovate … everything. It will touch almost every aspect in our everyday lives from Nano-Medicine and Consumer Electronics to Energy Solutions and Advanced Fabrics.” www.genesisnanotech.com – “Great Things from Small Things”
*** This article (From Forbes) originally appeared on PTC Product Lifecycle Stories.
It is hard to imagine the size of a nanometer. At one-billionth of a meter, a nanometer has been compared to 1/80,000th the diameter of a human hair, a million times smaller than the length of an ant, or the amount a man’s beard grows in the time it takes him to lift a razor to his face.
Yet, nanotechnology—the ability to control matter at the Nano-scale (approximately 1 to 100 nanometers)—is having a huge impact on science, engineering, and technology because matter behaves differently at that size.
The impact of nanotechnology on society has been compared to the invention of electricity or plastic—it is transformative to nearly everything we use today. Uses of nanotechnology range from applications for stronger golf clubs and stain-resistant pants to future visions of transforming manufacturing and treating cancer.
What’s so special about nanotechnology?
Nanotechnology and nanoscience involve the ability to see and to control individual atoms and molecules. At nanoscale, matter has unique physical, chemical, and biological properties that enable new applications. Some nanostructured materials are stronger or have different magnetic properties; some are better at conducting heat or electricity, or may become more chemically reactive, reflect light better, or change color as their size or structure is altered.
According to an article in ASME.org, nanotechnology “will leave virtually no aspect of life untouched and is expected to be in widespread use by 2020.” In addition, a policy paper by the National Academy of Agricultural Sciences (NAAS) describes nanotechnology as modern history’s “sixth revolutionary technology,” following the industrial revolution in the mid-1700s, nuclear energy revolution in the 1940s, green revolution in the 1960s, information technology revolution in the 1980s, and biotechnology revolution in the 1990s.
NISKAYUNA, N.Y. (AP) — New York state is teaming with General Electric Co. and other companies on a $500 million initiative to spur high-tech manufacturing of miniature electronics, Gov. Andrew Cuomo and GE CEO Jeffrey Immelt announced Tuesday.
The U.S. federal government is backing nanotech, and the 2015 Federal Budget provides more than $1.5 billion for the National Nanotechnology Initiative (NNI), a continued investment which supports the President’s technology innovation strategy.
Preparing for opportunity
Engineers with expertise in nanotechnology are becoming increasingly valuable, and universities are starting to offer programs focused on nanotech for engineering students.
Boston University, Rice University, Florida Polytechnic University, and Villanova are just some of the schools that have programs focused on nanotech, which promises to be a growing field. A listing of Nanotechnology Degree Programs shows the various bachelors, masters, and doctorate programs available in countries around the world which will prepare engineers for future jobs in nanotechnology. According to the National Nanotechnology Initiative, more than 150,000 people in the U.S. held jobs in nanotechnology in 2008, and by 2015 that number is expected to grow to 800,000.
As nanotechnology gains momentum and starts to touch many facets of our lives, countries around the globe are investing in this technology which has relatively low barriers to entry. The promise of nanotechnology is being realized by the many companies who want to be gain a share of the market for nanotech-based products, which Global Industry Analysts estimates will be $3.3 trillion by 2018.
Duke University researchers have found a “roving detection system” on the surface of cells that may point to new ways of treating diseases like cancer, Parkinson’s disease and amyotrophic lateral sclerosis (ALS).
The cells, which were studied in nematode worms, are able to break through normal tissue boundaries and burrow into other tissues and organs—a crucial step in many normal developmental processes, ranging from embryonic development and wound-healing to the formation of new blood vessels.
But sometimes the process goes awry. Such is the case with metastatic cancer, in which cancer cells spread unchecked from where they originated and form tumors in other parts of the body.
“Cell invasion is one of the most clinically relevant yet least understood aspects of cancer progression,” said David Sherwood, an associate professor of biology at Duke.
Sherwood is leading a team that is investigating the molecular mechanisms that control cell invasion in both normal development and cancer, using a one-millimeter worm known as C. elegans.
At one point in C. elegans development, a specialized cell called the anchor cell breaches the dense, sheet-like membrane that separate the worm’s uterus from its vulva, opening up the worm’s reproductive tract.
Anchor cells can’t see, so they need some kind of signal to tell them where to break through. In a 2009 study, Sherwood and colleagues discovered that an extracellular cue called netrin orients the anchor cell so that it invades in the right direction.
In a new study appearing Aug. 25 in the Journal of Cell Biology, the team shows how receptors on the invasive cells essentially rove around the cell membrane “hunting” for the missing netrin signal that will guide the cell to the correct location.
The researchers used a video camera attached to a powerful microscope to take time-lapse movies of the slow movement of the C. elegans anchor cell during its invasion.
Their time-lapse analyses reveal that when netrin production is blocked, netrin receptors on the surface of the anchor cell periodically cluster, disperse and reassemble in a different region of the cell membrane. The receptors cluster alongside patches of actin filaments—thin flexible fibers that help cells change shape and form invasive protrusions –- that pop up in ea
“It’s kind of like a missile detection system,” Sherwood said.
Rather than the whole cell having to move around, its receptors move around on the outside of the cell until they get a signal. Once the receptors locate the netrin signal, they stabilize in the region of the cell membrane that is closest to the source of the signal.
The findings redefine decades-old ideas about how the cell’s navigation system works. “Cells don’t just passively respond to the netrin signal—they’re actively searching for it,” Sherwood said.
Given that netrin has been found to promote cell invasion in some of the most lethal cancers, the findings could lead to new treatment strategies. Disrupting the cell’s netrin detection system, for example, could prevent cancer cells from finding their way to the bloodstream or the lymphatic system and stop them from metastasizing, or becoming invasive and spreading throughout the body.
“One of the things we’re gearing up to do next are drug screens with our collaborators to see if we can block this detection system during invasion,” Sherwood said.
Scientists have also known for years that netrin plays a key role in wiring the brain and nervous system by guiding developing nerve cells as they grow and form connections.
This means the results could also point to new ways of treating neurological disorders like Parkinson’s and ALS and recovering from spinal cord injuries.
Tinkering with the cell’s netrin detection machinery, for example, may make it possible to encourage damaged cells in the central nervous system—which normally have limited ability to regenerate—to regrow.
Old thinking was that gold, while good for jewelry, was not of much use for chemists because it is relatively nonreactive. That changed a decade ago when scientists hit a rich vein of discoveries revealing that this noble metal, when structured into nanometer-sized particles, can speed up chemical reactions important in mitigating environmental pollutants and producing hard-to-make specialty chemicals.
Catalytic gold nanoparticles have since spurred hundreds of scientific journal articles. With the world catalyst market poised to hit $19.5 billion by 2016, gold nanoparticles may find commercial as well as intellectual importance, as they could ultimately lead to novel catalysts for energy, pharmacology and diverse consumer products.
The reaction mechanism of carbon monoxide oxidation is shown over intact and partially ligand-removed gold nanoclusters supported on cerium oxide rods. Image credit: Wu, Z.; Jiang, D.; Mann, A.; Mullins, D.; Qiao, Z.-A.; Allard, L.; Zeng, C.; Jin, R.; Overbury, S. Thiolate Ligands as a Double-Edged Sword for CO Oxidation on CeO2-Supported Au25(SCH2CH2Ph)18 Nanoclusters. J. Am. Chem. Soc. 2014, 136(16), 6111.
But before gold nanoparticles can be useful to consumers, researchers have to make them both stable and active. Recently, scientists learned to make tiny, highly ordered clusters with very specific numbers of gold atoms that are stabilized by compounds called ligands. These stabilized gold clusters plus ligands may be thought of as large molecules. In collaboration with scientists from Carnegie Mellon University, researchers at the Department of Energy’s Oak Ridge National Laboratory have found one new gold molecule, a catalyst containing exactly 25 gold atoms, that is powerful as well as sophisticated. It catalyzes the conversion of a variety of molecules, including the transformation of poisonous carbon monoxide into harmless carbon dioxide, a reaction that may find application in devices near gas flues or wood-burning stoves. Unfortunately, the ligands that create and stabilize the engineered clusters also block the very sites needed to catalyze the conversion of carbon monoxide into carbon dioxide.
“The ligands are double-edged swords,” said study leader Zili Wu of ORNL, whose investigation was conducted in ORNL’s catalysis group, which is led by Steve Overbury. “We’re interested in using gold clusters as catalysts or catalyst precursors. Ligands on the one hand stabilize the gold particle structure but on the other hand decrease their catalytic performance. Balancing those two factors is the key to creating a new catalytic system. One way is to utilize a metal oxide (here, cerium oxide) as an inorganic ligand to stabilize the gold clusters when the organic ligand has to be removed for catalysis.”
Many catalytic systems consist of metal particles with catalytic properties placed on a metal oxide support with catalytic properties of its own. The metal and metal oxide work together to create a new type of catalytic activity. “We’re trying to understand how that happens,” Wu said.
Their study, published in the Journal of the American Chemical Society, described how ligands enabled the gold nanocluster to dock on a cerium oxide support shaped like a rod. The catalysts produced were all identical. The researchers would like to engineer future oxide supports in the shapes of cubes or octahedra to find out how those nanostructures could alter the configuration of the gold and the reactivity of the final component system. Better understanding of stabilizing agents may aid design of novel catalysts for critical chemical reactions including oxidation, hydrogenation and coupling.
Carnegie Mellon Professor Rongchao Jin, his student Chenjie Zeng and ORNL postdoctoral fellows Amanda Mann and Zhen-An Qiao synthesized the gold clusters. Mann made the cerium oxide rods. Wu and Mann placed the gold clusters on the supports and performed chemical reaction studies. David Mullins of ORNL performed measurements of extended X-ray absorption fine structure to learn how sizes of clusters change with temperature. ORNL’s Larry Allard verified the nature of the structures with aberration-corrected microscopy, and De-en Jiang, formerly of ORNL but now at the University of California–Riverside, used the Oak Ridge Institutional Cluster to computationally explore structures of ligand-bound gold clusters.
“These ligands affect the reactivity—they essentially poison the gold surface—so the gold really has to be activated,” Overbury, the study’s senior author, explained. “We put the gold onto a support, and it’s got these ligands protecting it. We have to remove those ligands, so we basically heat this [gold nanocluster] up or treat it in some gas to elevated temperatures.”
When the gold clusters are heated, the ligands start to come off and gold’s catalytic activity increases. The optimal temperature for producing gold nanocluster catalysts for carbon monoxide oxidation is 498 Kelvin (225 degrees Celsius or 437 degrees Fahrenheit), Wu said. If heating increases further, catalytic activity decreases because the gold particles become fluid and aggregate on the support.
Next the scientists are interested in varying the gold-cluster size and stabilizing the new clusters to make novel uniform catalysts. “We want to understand how other kinds of reactions can be catalyzed by these. So far we’ve only looked at carbon monoxide oxidation, which is kind of a test reaction,” Overbury said. “Our primary interest is using the gold-nanocluster complex as a toolbox for learning about how other complex reactions occur.”
Added Overbury, “We’re only just starting to mine all the catalytic possibilities for gold.”
DOE’s Office of Science sponsored the research described in the Journal of the American Chemical Society paper. Raman and Fourier transform infrared spectroscopies and catalytic measurements were conducted at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL. Extended X-ray absorption fine structure work was performed at the National Synchrotron Light Source, which is also a DOE Office of Science User Facility, at Brookhaven National Laboratory.
UT-Battelle manages ORNL for DOE’s Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time.
Reference: Wu, Z.; Jiang, D.; Mann, A.; Mullins, D.; Qiao, Z.-A.; Allard, L.; Zeng, C.; Jin, R.; Overbury, S. Thiolate Ligands as a Double-Edged Sword for CO Oxidation on CeO2-Supported Au25(SCH2CH2Ph)18 Nanoclusters. J. Am. Chem. Soc. 2014, 136(16), 6111.
Source: By Dawn Levy, Oakridge National Laboratory
20 Aug 2014
IBM Researchers build solar concentrator that generates electricity and enough heat for desalination or cooling.
Researchers envision giant concentrators, built with low-cost materials, that produce electricity and heat for use in desalination or cooling. Credit: IBM Research.
Cooling a supercomputer can provide clues on how to make solar power cheap, says IBM.
IBM Research today detailed a prototype solar dish that uses a water-cooling technology it developed for its high-end computers (see “Hot Water Helps Super-Efficient Supercomputer Keep Its Cool”). The solar concentrator uses low-cost components and produces both electricity and heat, which could be used for desalination or to run an air conditioner.
The work, funded by $2.4 million grant from the Swiss Commission for Technology and Innovation, is being done by IBM Research, the Swiss company Airlight Energy, and Swiss researchers. Since this is outside IBM’s main business, it’s not clear how the technology would be commercialized. But the high-concentration photovoltaic thermal (HCPVT) system promises to be cost-effective, according to IBM, and the design offers some insights into how to use concentrating solar power for both heat and electricity.
Typically, parabolic dishes concentrate sunlight to produce heat, which can be transfered to another machine or used to drive a Stirling engine that makes electricity (see “Running a Marine Unit on Solar and Diesel”). With this device, IBM and its partners used a solar concentrator dish to shine light on a thin array of highly efficient triple-junction solar cells, which produce electricity from sunlight. By concentrating the light 2,000 times onto hundreds of one-centimeter-square cells, IBM projects, a full-scale concentrator could provide 25 kilowatts of power.
In this design, the engineers hope to both boost the output of the solar cells and make use of the heat produced by the concentrator. Borrowing its liquid-cooling technology for servers, IBM built a cooling system with pipes only a few microns off the photovoltaic cells to circulate water and carry away the heat. More than 50 percent of the waste heat is recovered. “Instead of just throwing away the heat, we’re using the waste heat for processes such as desalination or absorption cooling,” says Bruno Michel, manager, advanced thermal packaging at IBM Research.
Researchers expect they can keep the cost down with a tracking system made out of concrete rather than metal. Instead of mirrored glass on the concentrator dish, they plan to use metal foils. They project the cost to be 10 cents per kilowatt-hour in desert regions that have the appropriate sunlight, such as the Sahara in northern Africa.
One of the primary challenges of such a device, apart from keeping costs down and optimizing efficiency, is finding a suitable application. The combined power and thermal generator only makes sense in places where the waste heat can be used at least during part of the day. The researchers envision it could be used in sunny locations without adequate fresh water reserves or, potentially, in remote tourist resorts on islands. In those cases, the system would need to be easy to operate and reliable.
Sulfur is a very intriguing solution for the design of high energy density storage devices. The lithium-sulfur battery theoretically delivers energy density of 2600 Wh kg-1, which is 3-5 times higher than traditional lithium-ion batteries. Copyright Michael Berger
Unfortunately, several obstacles so far have prevented the practical demonstration of sulfur-based cathodes for Li-S batteries. Among them, the most important one is the rapid capacity fading. “The fast capacity decay of lithium-sulfur battery is ascribed to multifaceted aspects,” Dr. Qiang Zhang, an associate professor at Department of Chemical Engineering at Tsinghua University, tells Nanowerk. “One of the most widely accepted reasons is assigned to the intermediate polysulfides.” Polysulfides are a variety of transition forms of partially lithiated sulfur, which is highly polar and soluble in organic electrolytes. During discharge, they dissolve in the electrolyte, diffuse from cathode to anode, and react with the lithium anode.
“The active materials lose in this way, undoubtedly causing capacity fading,” says Zhang. “While considerable research endeavor is dedicated to solving this problem, what we are interested in is another rarely addressed issue regarding the capacity fading: the dynamic fluctuation of affinity between different sulfur species and conductive host materials.” He continues to explain that, because of the multi-electron-transfer process, sulfur species vary from the initial elemental sulfur, intermediate polysulfides, and final discharge product of lithium sulfides. “Sulfur is unpolar, thus exhibits highest affinity to conventional carbon hosts,” he says. “But polysulfides and lithium sulfides are highly polar, weakening the interaction between them and carbon.
Due to this poor interaction, they easily detach from the carbon host and contribute no capacity. As a result, the performance of a lithium-sulfur battery deteriorates rapidly when only pure carbon hosts is employed.” Consequently, he concludes, the key issue lies in how to choose an ideal host material with high affinity to both unpolar sulfur and polar polysulfides, as well as lithium sulfides.
In new work published in the July 24, 2014 online edition of Advanced Materials Interfaces (“Strongly Coupled Interfaces between a Heterogeneous Carbon Host and a Sulfur-Containing Guest for Highly Stable Lithium-Sulfur Batteries: Mechanistic Insight into Capacity Degradation”), Zhang and his collaborators developed a novel strategy towards highly stable Li-S batteries by building a strongly coupled interface between surface- mediated carbon hosts and various sulfur-containing guests.
Schematic illustration of strongly coupled interfaces between N-doped carbon host and S-containing guest for highly stable Li-S battery. (Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
In this work, the team used nitrogen-doped carbon nanotubes as host material for the sulfur cathode: Nitrogen atoms with higher electronegativity are incorporated into the graphitic lattices of pristine carbon nanotubes, thereby providing a capability to tune their electronic structure and surface properties.
How do the doping nitrogen atoms affect the electrochemical behavior when nitrogen-doped carbon nanotubes are applied to lithium-sulfur battery? Hong-Jie Peng, a graduate student in Zhang’s group and the paper’s first author, answers this question:
“Firstly, we conducted a density functional theory (DFT) study and designed three molecular models to illustrate pure carbon, carbon with nitrogen at the edge – which we called pyridinic nitrogen – and carbon with nitrogen substituting the central carbon atom, which we called quaternary nitrogen.” “Through theoretical calculations, we found that nitrogen-doped carbon nanotubes exhibited stronger interaction with polysulfides and lithium sulfides,” he continues. “This is attributed to the adsorption of these polar sulfur species on the negatively charged nitrogen-doped sites.
It revealed that nitrogen-doped carbon nanotubes might be worth trying as host materials.” In their experiments, the team then prepared nitrogen-doped carbon nanotube/sulfur composites and assembled batteries to check if their theoretical results were reliable. “We were very happy to see that the electrochemical experiment matched our theoretical prediction very well,” says Peng.
“Compared to pristine carbon nanotubes-based host materials, the cycling life was significantly enhanced by six times.” In conclusion, this work highlights the importance of a stable dynamic interface between carbon hosts and sulfur-containing guests and sheds new light on the lithium-sulfur battery decay mechanism. “In fact” says Zhang, “the concept of building heterogeneous cathode scaffold won’t stop here. More advanced host materials satisfying the demand of amphiphilicity to both unpolar and polar sulfur species need to be explored.”
19 Aug 2014
|Source: Rochester Institute of Technology|
18 Aug 2014
Mark Lundstrom, a professor of electrical and computer engineering at Purdue University, discusses converging technologies at the National Science Foundation. This video is part of a series produced by NSF and the Science & Technology Innovation Program at the Woodrow Wilson International Center for Scholars.
For more information, please visit: http://www.wilsoncenter.org/convergence