13 Jun 2016
Scientists at UC San Diego, MIT and Harvard University have engineered “topological plexcitons,” energy-carrying particles that could help make possible the design of new kinds of solar cells and miniaturized optical circuitry.
The researchers report their advance in an article published in the current issue of Nature Communications.
Within the Lilliputian world of solid state physics, light and matter interact in strange ways, exchanging energy back and forth between them.
“When light and matter interact, they exchange energy,” explained Joel Yuen-Zhou, an assistant professor of chemistry and biochemistry at UC San Diego and the first author of the paper. “Energy can flow back and forth between light in a metal (so called plasmon) and light in a molecule (so called exciton). When this exchange is much faster than their respective decay rates, their individual identities are lost, and it is more accurate to think about them as hybrid particles; excitons and plasmons marry to form plexcitons.”
Materials scientists have been looking for ways to enhance a process known as exciton energy transfer, or EET, to create better solar cells as well as miniaturized photonic circuits which are dozens of times smaller than their silicon counterparts.
“Understanding the fundamental mechanisms of EET enhancement would alter the way we think about designing solar cells or the ways in which energy can be transported in nanoscale materials,” said Yuen-Zhou.
The drawback with EET, however, is that this form of energy transfer is extremely short-ranged, on the scale of only 10 nanometers, and quickly dissipates as the excitons interact with different molecules.
One solution to avoid those shortcomings is to hybridize excitons in a molecular crystal with the collective excitations within metals to produce plexcitons, which travel for 20,000 nanometers, a length which is on the order of the width of human hair.
Plexcitons are expected to become an integral part of the next generation of nanophotonic circuitry, light-harvesting solar energy architectures and chemical catalysis devices. But the main problem with plexcitons, said Yuen-Zhou, is that their movement along all directions, which makes it hard to properly harness in a material or device.
He and a team of physicists and engineers at MIT and Harvard found a solution to that problem by engineering particles called “topological plexcitons,” based on the concepts in which solid state physicists have been able to develop materials called “topological insulators.”
“Topological insulators are materials that are perfect electrical insulators in the bulk but at their edges behave as perfect one-dimensional metallic cables,” Yuen-Zhou said. “The exciting feature of topological insulators is that even when the material is imperfect and has impurities, there is a large threshold of operation where electrons that start travelling along one direction cannot bounce back, making electron transport robust. In other words, one may think about the electrons being blind to impurities.”
Plexcitons, as opposed to electrons, do not have an electrical charge. Yet, as Yuen-Zhou and his colleagues discovered, they still inherit these robust directional properties. Adding this “topological” feature to plexcitons gives rise to directionality of EET, a feature researchers had not previously conceived. This should eventually enable engineers to create plexcitonic switches to distribute energy selectively across different components of a new kind of solar cell or light-harvesting device.
More information: Nature Communications, DOI: 10.1038/NCOMMS11783
Genesis Nanotechnology, Inc. ~ “Great Things from Small Things”
13 Jun 2016
Australian researchers at the University of Adelaide have developed a method for embedding light-emitting nanoparticles into glass without losing any of their unique properties – a major step towards ‘smart glass’ applications such as 3D display screens or remote radiation sensors.
This new “hybrid glass” successfully combines the properties of these special luminescent (or light-emitting) nanoparticles with the well-known aspects of glass, such as transparency and the ability to be processed into various shapes including very fine optical fibres.
The research, in collaboration with Macquarie University and University of Melbourne, has been published online in the journal Advanced Optical Materials.
“These novel luminescent nanoparticles, called upconversion nanoparticles, have become promising candidates for a whole variety of ultra-high tech applications such as biological sensing, biomedical imaging and 3D volumetric displays,” says lead author Dr Tim Zhao, from the University of Adelaide’s School of Physical Sciences and Institute for Photonics and Advanced Sensing (IPAS).
“Integrating these nanoparticles into glass, which is usually inert, opens up exciting possibilities for new hybrid materials and devices that can take advantage of the properties of nanoparticles in ways we haven’t been able to do before. For example, neuroscientists currently use dye injected into the brain and lasers to be able to guide a glass pipette to the site they are interested in. If fluorescent nanoparticles were embedded in the glass pipettes, the unique luminescence of the hybrid glass could act like a torch to guide the pipette directly to the individual neurons of interest.”
Although this method was developed with upconversion nanoparticles, the researchers believe their new ‘direct-doping’ approach can be generalised to other nanoparticles with interesting photonic, electronic and magnetic properties. There will be many applications – depending on the properties of the nanoparticle.
“If we infuse glass with a nanoparticle that is sensitive to radiation and then draw that hybrid glass into a fibre, we could have a remote sensor suitable for nuclear facilities,” says Dr Zhao.
To date, the method used to integrate upconversion nanoparticles into glass has relied on the in-situ growth of the nanoparticles within the glass.
“We’ve seen remarkable progress in this area but the control over the nanoparticles and the glass compositions has been limited, restricting the development of many proposed applications,” says project leader Professor Heike Ebendorff-Heideprem, Deputy Director of IPAS.
“With our new direct doping method, which involves synthesizing the nanoparticles and glass separately and then combining them using the right conditions, we’ve been able to keep the nanoparticles intact and well dispersed throughout the glass. The nanoparticles remain functional and the glass transparency is still very close to its original quality. We are heading towards a whole new world of hybrid glass and devices for light-based technologies.”
Explore further: Ancient Roman glass inspires modern science
More information: Jiangbo Zhao et al. Upconversion Nanocrystal-Doped Glass: A New Paradigm for Photonic Materials, Advanced Optical Materials(2016). DOI: 10.1002/adom.201600296
Large quantities of steel are used in architecture, bridge construction and ship-building. Structures of this type are intended to be long-lasting. Furthermore, even in the course of many years, they must not lose any of their qualities regarding strength and safety. For this reason, the steel plates and girders used must have extensive and durable protection against corrosion. In particular, the steel is attacked by oxygen in the air, water vapor and salts. Nowadays, various techniques are used to prevent the corrosive substances from penetrating into the material. One common method is to create an anti-corrosion coating by applying layers of zinc-phosphate. Now, research scientists at INM — Leibniz Institute for New Materials developed a special type of zinc-phosphate nanoparticles. In contrast to conventional, spheroidal zinc-phosphate nanoparticles, the new nanoparticles are flake-like. They are ten times as long as they are thick. As a result of this anisotropy, the penetration of gas molecules into the metal is slowed down.
The developers will be demonstrating their results and the possibilities they offer at stand B46 in hall 2 at this year’s Hanover Trade Fair as part of the leading trade show Research & Technology which takes place from 25th to 29th April.
“In first test coatings, we were able to demonstrate that the flake-type nanoparticles are deposited in layers on top of each other thus creating a wall-like structure,” explained Carsten Becker-Willinger, Head of Nanomers® at INM. “This means that the penetration of gas molecules through the protective coating is longer because they have to find their way through the ´cracks in the wall´.” The result, he said, was that the corrosion process was much slower than with coatings with spheroidal nanoparticles where the gas molecules can find their way through the protective coating to the metal much more quickly.
In further series of tests, the scientists were able to validate the effectiveness of the new nanoparticles. To do so, they immersed steel plates both in electrolyte solutions with spheroidal zinc-phosphate nanoparticles and with flake-type zinc-phosphate nanoparticles in each case. After just half a day, the steel plates in the electrolytes with spheroidal nanoparticles were showing signs of corrosion whereas the steel plates in the electrolytes with flake-type nanoparticles were still in perfect condition and shining, even after three days. The researchers created their particles using standard, commercially available zinc salts, phosphoric acid and an organic acid as a complexing agent. The more complexing agent they added, the more anisotropic the nanoparticles became.
INM conducts research and development to create new materials — for today, tomorrow and beyond. Chemists, physicists, biologists, materials scientists and engineers team up to focus on these essential questions: Which material properties are new, how can they be investigated and how can they be tailored for industrial applications in the future?
Four research thrusts determine the current developments at INM:
- New materials for energy application,
- New concepts for medical surfaces,
- New surface materials for tribological systems and
- Nano safety and nano bio.
Research at INM is performed in three fields: Nanocomposite Technology, Interface Materials, and Bio Interfaces. INM — Leibniz Institute for New Materials, situated in Saarbrücken, is an internationally leading center for materials research. It is an institute of the Leibniz Association and has about 220 employees.
Photo: M. Scott Brauer
National public-private consortium led by MIT will involve manufacturers, universities, agencies, companies.
A wide range of industries are expected to benefit from these revolutionary fibers and textiles, including apparel, consumer products, automotive, medical devices, and consumer electronics. “Fibers and fabrics are ubiquitous,” Fink says. “Our institute will go everywhere a fiber and fabric goes.”
An independent nonprofit founded by MIT has been selected to run a new, $317 million public-private partnership announced today by Secretary of Defense Ashton Carter.
The partnership, named the Advanced Functional Fibers of America (AFFOA) Institute, has won a national competition for federal funding to create the latest Manufacturing Innovation Institute. It is designed to accelerate innovation in high-tech, U.S.-based manufacturing involving fibers and textiles.
The proposal for the institute was led by Professor Yoel Fink, director of MIT’s Research Laboratory of Electronics (RLE). The partnership includes 32 universities, 16 industry members, 72 manufacturing entities, and 26 startup incubators, spread across 27 states and Puerto Rico.
This is the eighth Manufacturing Innovation Institute established to date, and the first to be headquartered in New England. The headquarters will be established in Cambridge, Massachusetts, in proximity to the MIT campus and its U.S. Army-funded Institute for Soldier Nanotechnology, as well as the Natick Soldier Research Development and Engineering Center.
This unique partnership, Fink says, has the potential to create a whole new industry, based on breakthroughs in fiber materials and manufacturing. These new fibers and the fabrics made from them will have the ability to see, hear, and sense their surroundings; communicate; store and convert energy; monitor health; control temperature; and change their color.
The new initiative will receive $75 million in federal funding out of a total of $317 million through cost sharing among the Department of Defense, industrial partners, venture capitalists, universities, nonprofits, and states including the Commonwealth of Massachusetts. The initial funding will cover a five-year period and will be administered through the new, independent, nonprofit organization set up for the purpose. The partnership, which will focus on both developing new technologies and training the workforce needed to operate and maintain these production systems, also includes a network of community colleges and experts in career and technical education for manufacturing.
“Massachusetts’s innovation ecosystem is reshaping the way that people interact with the world around them,” says Massachusetts Gov. Charlie Baker. “This manufacturing innovation institute will be the national leader in developing and commercializing textiles with extraordinary properties. It will extend to an exciting new field our ongoing efforts to nurture emerging industries, and grow them to scale in Massachusetts. And it will serve as a vital piece of innovation infrastructure, to support the development of the next generation of manufacturing technology, and the development of a highly skilled workforce.”
“Through this manufacturing innovation institute, Massachusetts researchers and Massachusetts employers will collaborate to unlock new advances in military technology, medical care, wearable technology, and fashion,” adds Massachusetts Lt. Gov. Karyn Polito. “This, in turn, will help drive business expansion, support the competitiveness of local manufacturers, and create new employment opportunities for residents across the Commonwealth.”
Announcing the new institute at an event at MIT, Carter stressed the importance of technology and innovation to the mission of the Department of Defense and to national security broadly: “The intersection of the two is truly an opportunity-rich environment. These issues matter. They have to do with our protection and our security, and creating a world where our fellow citizens can go to school and live their lives, and dream their dreams, and one day give their children a better future. Helping defend your country and making a better world is one of the noblest things that a business leader, a technologist, an entrepreneur, or a young person can do, and we’re all grateful to all of you for doing that with us.”
A new age of fabrics
For thousands of years, humans have used fabrics in much the same way, to provide basic warmth and aesthetics. Clothing represents “one of the most ancient forms of human expression,” Fink says, but one that is now, for the first time, poised to undergo a profound transformation — the dawn of a “fabric revolution.”
“What makes this point in time different? The answer is research,” Fink says: Objects that serve many complex functions are always made of multiple materials, whereas single-material objects, such as a drinking glass, usually have just a single, simple function. But now, new technology — some of it developed in Fink’s own laboratory — is changing all that, making it possible to integrate many materials and complex functional structures into a fabric’s very fibers, and to create fiber-based devices and functional fabric systems.
The semiconductor industry has shown how to combine millions of transistors into an integrated circuit that functions as a system; as described by “Moore’s law,” the number of devices and functions has doubled in computer chips every couple of years. Fink says the team envisions that the number of functions in a fiber will grow with similar speed, paving the way for highly functional fabrics.
The challenge now is to execute this vision, Fink says. While many textile and apparel companies and universities have figured out pieces of this puzzle, no single one has figured it all out.
“It turns out there is no company or university in the world that knows how to do all of this,” Fink says. “Instead of creating a single brick-and-mortar center, we set out to assemble and organize companies and universities that have manufacturing and ‘making’ capabilities into a network — a ‘distributed foundry’ capable of addressing the manufacturing challenges. To date, 72 manufacturing entities have signed up to be part of our network.”
“With a capable manufacturing network in place,” Fink adds, “the question becomes: How do we encourage and foster product innovation in this new area?” The answer, he says, lies at the core of AFFOA’s activities: Innovators across the country will be invited to execute “advanced fabric” products on prototyping and pilot scales. Moreover, the center will link these innovators with funding from large companies and venture capital investors, to execute their ideas through the manufacturing stage. The center will thus lower the barrier to innovation and unleash product creativity in this new domain, he says.
Promoting leadership in manufacturing
The federal selection process for the new institute was administered by the U.S. Department of Defense’s Manufacturing Technology Program and the U.S. Army’s Natick Soldier Research, Development and Engineering Center and Contracting Command in New Jersey. Retired Gen. Paul J. Kern will serve as chairman of the AFFOA Institute.
As explained in the original call for proposals to create this institute, the aim is to ensure “that America leads in the manufacturing of new products from leading edge innovations in fiber science, commercializing fibers and textiles with extraordinary properties. Known as technical textiles, these modern day fabrics and fibers boast novel properties ranging from being incredibly lightweight and flame resistant, to having exceptional strength. Technical textiles have wide-ranging applications, from advancing capabilities of protective gear allowing fire fighters to battle the hottest flames, to ensuring that a wounded soldier is effectively treated with an antimicrobial compression bandage and returned safely.”
In addition to Fink, the new partnership will include Tom Kochan, the George Maverick Bunker Professor of Management at MIT’s Sloan School of Management, who will serve as chief workforce officer coordinating the nationwide education and workforce development (EWD) plan. Pappalardo Professor of Mechanical Engineering Alexander Slocum will be the EWD deputy for education innovation. Other key MIT participants will include professors Krystyn Van Vliet from the Materials Science and Engineering and Biological Engineering departments; Peko Hosoi and Kripa Varanasi from the Department of Mechanical Engineering; and Gregory Rutledge from the Department of Chemical Engineering.
Among the industry partners who will be members of the partnership are companies such as Warwick Mills, DuPont, Steelcase, Nike, and Corning. Among the academic partners are Drexel University, the University of Massachusetts at Amherst, the University of Georgia, the University of Tennessee, and the University of Texas at Austin.
In a presentation last fall about the proposed partnership, MIT President L. Rafael Reif said, “We believe that partnerships — with industry and government and across academia — are critical to our capacity to create positive change.” He added, “Our nation has no shortage of smart, ambitious people with brilliant new ideas. But if we want a thriving economy, producing more and better jobs, we need more of those ideas to get to market faster.” Accelerating such implementation is at the heart of the new partnership’s goals.
Connecting skills, workers, and jobs
This partnership, Reif said, will be “a system that connects universities and colleges with motivated companies and with far-sighted government agencies, so we can learn from each other and work with each other. A system that connects workers with skills, and skilled workers with jobs. And a system that connects advanced technology ideas to the marketplace or to those who can get them to market.”
Part of the power of this new collaboration, Fink says, is combining the particular skills and resources of the different partners so that they “add up to something that’s more than the sum of the parts.” Existing large companies can contribute both funding and expertise, smaller startup companies can provide their creative new ideas, and the academic institutions can push the research boundaries to open up new technological possibilities.
“MIT recognizes that advancing manufacturing is vital to our innovation process, as we explored in our Production in the Innovation Economy (PIE) study,” says MIT Provost Martin Schmidt. “AFFOA will connect our campus even more closely with industries (large and small), with educational organizations that will develop the skilled workers, and with government at the state and federal level — all of whom are necessary to advance this new technology. AFFOA is an exciting example of the public-private partnerships that were envisioned in the recommendation of the Advanced Manufacturing Partnership.”
“Since MIT’s start, there has always been an emphasis on ‘mens et manus,’ using our minds and hands to make inventions useful at scales that impact the nation and the world,” adds Van Vliet, the director of manufacturing innovation for MIT’s Innovation Initiative, who has served as the faculty lead in coordinating MIT’s response to manufacturing initiatives that result from the Advanced Manufacturing Partnership. “What makes this new partnership very exciting is, this is for the first time a manufacturing institute headquartered in our region that connects our students and our faculty with local and national industrial partners, to really scale up production of many new fiber and textile technologies.”
“Participating in this group of visionaries from government, academia, and industry — who are all motivated by the goal of advancing a new model of American textile manufacturing and helping to develop new products for the public and defense sectors — has been an exciting process,” says Aleister Saunders, Drexel University’s senior vice provost for research and a leader of its functional fabrics center. “Seeing the success we’ve already had in recruiting partners at the local level leads me to believe that on a national level, these centers of innovation will be able to leverage intellectual capital and regional manufacturing expertise to drive forward new ideas and new applications that will revolutionize textile manufacturing across the nation.”
“Revolutionary fabrics and fibers are modernizing everything from battlefield communication to medical care,” says U.S. Congressmen Joe Kennedy III (D-Mass.). “That the Commonwealth would be chosen to lead the way is no surprise. From Lowell to Fall River, our ability to merge cutting-edge technology with age-old ingenuity has sparked a new day for the textile industry. With its unparalleled commitment to innovation, MIT is the perfect epicenter for scaling these efforts. I applaud President Reif, Professor Fink, and all of the partners involved for this tremendous success.”
The innovations that led to the “internet of things” and the widespread incorporation of digital technology into manufacturing have brought about a revolution whose potential is unlimited and will generate “brilliant ideas that people will be able to bring to this task of making sure that America stays number one in each and every one of these fields,” said Senator Ed Markey (D-Mass.) at the MIT event. “The new institute we are announcing today will help ensure that both Massachusetts and the United States can expand our technological edge in a new generation of fiber science.”
A wide range of industries are expected to benefit from these revolutionary fibers and textiles, including apparel, consumer products, automotive, medical devices, and consumer electronics. “Fibers and fabrics are ubiquitous,” Fink says. “Our institute will go everywhere a fiber and fabric goes.”
Genesis Nanotechnology, Inc. ~ “Great Things from Small Things”
A Rice University laboratory has found a way to turn common carbon fiber into graphene quantum dots, tiny specks of matter with properties expected to prove useful in electronic, optical and biomedical applications.
The Rice lab of materials scientist Pulickel Ajayan, in collaboration with colleagues in China, India, Japan and the Texas Medical Center, discovered a one-step chemical process that is markedly simpler than established techniques for making graphene quantum dots. The results were published online this month in the American Chemical Society’s journal Nano Letters.
“There have been several attempts to make graphene-based quantum dots with specific electronic and luminescent properties using chemical breakdown or e-beam lithography of graphene layers,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science and of Chemistry. “We thought that as these nanodomains of graphitized carbons already exist in carbon fibers, which are cheap and plenty, why not use them as the precursor?”
Quantum dots, discovered in the 1980s, are semiconductors that contain a size- and shape-dependent band gap. These have been promising structures for applications that range from computers, LEDs, solar cells and lasers to medical imaging devices. The sub-5 nanometer carbon-based quantum dots produced in bulk through the wet chemical process discovered at Rice are highly soluble, and their size can be controlled via the temperature at which they’re created.
The Rice researchers were attempting another experiment when they came across the technique. “We tried to selectively oxidize carbon fiber, and we found that was really hard,” said Wei Gao, a Rice graduate student who worked on the project with lead author Juan Peng, a visiting student from Nanjing University who studied in Ajayan’s lab last year. “We ended up with a solution and decided to look at a few drops with a transmission electron microscope.”
The specks they saw were bits of graphene or, more precisely, oxidized nanodomains of graphene extracted via chemical treatment of carbon fiber. “That was a complete surprise,” Gao said. “We call them quantum dots, but they’re two-dimensional, so what we really have here are graphene quantum discs.” Gao said other techniques are expensive and take weeks to make small batches of graphene quantum dots. “Our starting material is cheap, commercially available carbon fiber. In a one-step treatment, we get a large amount of quantum dots. I think that’s the biggest advantage of our work,” she said.
Further experimentation revealed interesting bits of information: The size of the dots, and thus their photoluminescent properties, could be controlled through processing at relatively low temperatures, from 80 to 120 degrees Celsius. “At 120, 100 and 80 degrees, we got blue, green and yellow luminescing dots,” she said.
They also found the dots’ edges tended to prefer the form known as zigzag. The edge of a sheet of graphene — the single-atom-thick form of carbon — determines its electrical characteristics, and zigzags are semiconducting.
Their luminescent properties give graphene quantum dots potential for imaging, protein analysis, cell tracking and other biomedical applications, Gao said. Tests at Houston’s MD Anderson Cancer Center and Baylor College of Medicine on two human breast cancer lines showed the dots easily found their way into the cells’ cytoplasm and did not interfere with their proliferation.
“The green quantum dots yielded a very good image,” said co-author Rebeca Romero Aburto, a graduate student in the Ajayan Lab who also studies at MD Anderson. “The advantage of graphene dots over fluorophores is that their fluorescence is more stable and they don’t photobleach. They don’t lose their fluorescence as easily. They have a depth limit, so they may be good for in vitro and in vivo (small animal) studies, but perhaps not optimal for deep tissues in humans.
“But everything has to start in the lab, and these could be an interesting approach to further explore for bioimaging,” Romero Alburto said. “In the future, these graphene quantum dotscould have high impact because they can be conjugated with other entities for sensing applications, too.”
Explore further: Single Atom Quantum Dots Bring Real Devices Closer (Video)
More information: Nano Lett., Article ASAP DOI: 10.1021/nl2038979
Ciphers and invisible ink – many of us experimented with these when we were children. A team of Chinese scientists has now developed a clever, high-tech version of “invisible ink”. As reported in the journal Angewandte Chemie, the ink is based on carbon nitride quantum dots. Information written with this ink is not visible under ambient or UV light; however, it can be seen with a fluorescence microplate reader. The writing can be further encrypted or decrypted by quenching or recovering the fluorescence with different reagents.
Fluorescing security inks are primarily used to ensure the authenticity of products or documents, such as certificates, stock certificates, transport documents, currency notes, or identity cards. Counterfeits may cost affected companies lost profits, and the poor quality of the false products may damage their reputations. In the case of sensitive products like pharmaceuticals and parts for airplanes and cars, human lives and health may be endangered. Counterfeiters have discovered how to imitate UV tags but it is significantly harder to copy security inks that are invisible under UV light.
Researchers working with Xinchen Wang and Liangqia Guo at Fuzhou University have now introduced an inexpensive “invisible” ink that increases the security of encoded data while also making it possible to encrypt and decrypt secure information.
The new ink is based on water-soluble quantum dots, nanoscopic “heaps” of a semiconducting material. Quantum dots have special optoelectronic properties that can be controlled by changing the size of the dots.
The scientists used quantum dots made from graphitic carbon nitride. This material consists of ring systems made of carbon and nitrogen atoms linked into two-dimensional molecular layers. The structure is similar to that of graphite (or graphene), one of the forms of pure carbon, but also has semiconductor properties.
Information written with this new ink is invisible under ambient and UV light because it is almost transparent in the visible light range and emits fluorescence with a peak in the UV range. The writing only becomes visible under a microplate reader like those used in biological fluorescence tests. In addition, the writing can be further encrypted and decrypted: treatment with oxalic acid renders it invisible to the microplate reader. Treatment with sodium bicarbonate reverses this process, making the writing visible to the reader once more.
Explore further: Luminescent ink from eggs
More information: Zhiping Song et al. Invisible Security Ink Based on Water-Soluble Graphitic Carbon Nitride Quantum Dots, Angewandte Chemie International Edition (2016). DOI: 10.1002/anie.201510945
Journal reference: Angewandte Chemie Angewandte Chemie International Edition
Provided by: Angewandte Chemie
31 Mar 2016
Recently, researchers at Tsinghua University, China have proposed a graphene-based nanostructured lithium metal anode for lithium metal batteries to inhibit dendrite growth and improve electrochemistry performance. They report their findings in Advanced Materials, published on March 16, 2016.
“Widely used lithium-ion batteries cannot satisfy the increasing requirement of energy storage systems in portable electronics and electric vehicles. New lithium metal anode batteries, like Li-S and Li-air batteries, are highly sought. Lithium metal provides an extremely high theoretical specific capacity, which is almost 10 times more energy than graphite,” said Prof. Qiang Zhang, at the Department of Chemical Engineering, Tsinghua University. “However, the practical applications of lithium metals are strongly hindered by lithium dendrite growth in continuous cycles. This induces safety concerns. The lithium dendrites may cause internal short circuits resulting in fire. Furthermore, the formation of lithium dendrites induces very low cycling efficiency.” The dendrite growth and unstable solid electrolyte interphase consume large amount of lithium and electrolyte, and therefore leading to irreversible battery capacity losses. Consequently, inhibiting the dendrites growth is highly expected.
Many approaches have been proposed to retard the growth of dendrites through electrolyte modification, artificial solid electrolyte interphase layers, electrode construction, and others. “We noticed that by decreasing the local current density heavily, lithium dendrite growth could be efficiently inhibited. Based on this concept, we employed unstacked graphene with an ultrahigh specific surface area to build a nanostructured anode. And it turned out to be a very efficient idea,” said Rui Zhang, a Ph.D. student and the first author. “Additionally, we have employed the dual-salt electrolyte to acquire more stable and more flexible solid electrolyte interphase, which can protect the lithium metal from further reactions with electrolyte.”
This graphene-based anode offered great improvement, including (1) ultralow local current density on the surface of graphene anode (a ten-thousandth of that on routine Cu foil-based anodes) induced by the large specific surface area of 1666 m2 g-1, which inhibited dendrite growth and brought uniform lithium deposition morphology; (2) high stable cycling capacity of 4.0 mAh mg-1 induced by the high pore volume (1.65 cm3 g-1) of unstacked graphene, over 10 times of the graphite anode in lithium-ion batteries (0.372 mAh mg-1); (3) high electrical conductivity (435 S cm-1), leading to low interface impedance, stable charging/discharging performance, and high cycling efficiencies.
“We hope that our research can point out a new strategy to deal with the dendrite challenge in lithium metal anodes. The ultralow local current density induced by conductive nanostructured anodes with high specific surface area can help improve the stability and electrochemistry performance of lithium metal anodes,” said Xin-Bing Cheng, a co-author of the work. Future investigation is required to design preferable anode structures and to produce more protective solid electrolyte interphase layers. The researchers also call for additional study of the diffusion behavior of Li ions and electrons in the process of lithium depositing and stripping to advance the commercial applications of lithium metal anodes.
Explore further: Nanostructure enlightening dendrite-free metal anode
More information: R. Zhang, X.-B. Cheng, C.-Z. Zhao, H.-J. Peng, J.-L. Shi, J.-Q. Huang, J. Wang, F. Wei, Q. Zhang. Conductive Nanostructured Scaffolds Render Low Local Current Density to Inhibit Lithium Dendrite Growth. Adv. Mater. 2016, 28, 2155-2162. DOI: 10.1002/adma.201504117.
Grid-scale approach to rechargeable power storage gets new arsenal of possible materials.
Liquid metal batteries, invented by MIT professor Donald Sadoway and his students a decade ago, are a promising candidate for making renewable energy more practical. The batteries, which can store large amounts of energy and thus even out the ups and downs of power production and power use, are in the process of being commercialized by a Cambridge-based startup company, Ambri.
Now, Sadoway and his team have found yet another set of chemical constituents that could make the technology even more practical and affordable, and open up a whole family of potential variations that could make use of local resources.
The latest findings are reported in the journal Nature Communications, in a paper by Sadoway, who is the John F. Elliott Professor of Materials Chemistry, and postdoc Takanari Ouchi, along with Hojong Kim (now a professor at Penn State University) and PhD student Brian Spatocco at MIT. They show that calcium, an abundant and inexpensive element, can form the basis for both the negative electrode layer and the molten salt that forms the middle layer of the three-layer battery.
That was a highly unexpected finding, Sadoway says. Calcium has some properties that made it seem like an especially unlikely candidate to work in this kind of battery. For one thing, calcium easily dissolves in salt, and yet a crucial feature of the liquid battery is that each of its three constituents forms a separate layer, based on the materials’ different densities, much as different liqueurs separate in some novelty cocktails. It’s essential that these layers not mix at their boundaries and maintain their distinct identities.
It was the seeming impossibility of making calcium work in a liquid battery that attracted Ouchi to the problem, he says. “It was the most difficult chemistry” to make work but had potential benefits due to calcium’s low cost as well as its inherent high voltage as a negative electrode. “For me, I’m happiest with whatever is most difficult,” he says — which, Sadoway points out, is a very typical attitude at MIT.
Another problem with calcium is its high melting point, which would have forced the liquid battery to operate at almost 900 degrees Celsius, “which is ridiculous,” Sadoway says. But both of these problems were solvable.
First, the researchers tackled the temperature problem by alloying the calcium with another inexpensive metal, magnesium, which has a much lower melting point. The resulting mix provides a lower operating temperature — about 300 degrees less than that of pure calcium — while still keeping the high-voltage advantage of the calcium.
The other key innovation was in the formulation of the salt used in the battery’s middle layer, called the electrolyte, that charge carriers, or ions, must cross as the battery is used. The migration of those ions is accompanied by an electric current flowing through wires that are connected to the upper and lower molten metal layers, the battery’s electrodes.
The new salt formulation consists of a mix of lithium chloride and calcium chloride, and it turns out that the calcium-magnesium alloy does not dissolve well in this kind of salt, solving the other challenge to the use of calcium.
But solving that problem also led to a big surprise: Normally there is a single “itinerant ion” that passes through the electrolyte in a rechargeable battery, for example, lithium in lithium-ion batteries or sodium in sodium-sulfur. But in this case, the researchers found that multiple ions in the molten-salt electrolyte contribute to the flow, boosting the battery’s overall energy output. That was a totally serendipitous finding that could open up new avenues in battery design, Sadoway says.
And there’s another potential big bonus in this new battery chemistry, Sadoway says. “There’s an irony here. If you’re trying to find high-purity ore bodies, magnesium and calcium are often found together,” he says. It takes great effort and energy to purify one or the other, removing the calcium “contaminant” from the magnesium or vice versa. But since the material that will be needed for the electrode in these batteries is a mixture of the two, it may be possible to save on the initial materials costs by using “lower” grades of the two metals that already contain some of the other.
“There’s a whole level of supply-chain optimization that people haven’t thought about,” he says.
Sadoway and Ouchi stress that these particular chemical combinations are just the tip of the iceberg, which could represent a starting point for new approaches to devising battery formulations. And since all these liquid batteries, including the original liquid battery materials from his lab and those under development at Ambri, would use similar containers, insulating systems, and electronic control systems, the actual internal chemistry of the batteries could continue to evolve over time. They could also adapt to fit local conditions and materials availability while still using mostly the same components.
“The lesson here is to explore different chemistries and be ready for changing market conditions,” Sadoway says. What they have developed “is not a battery; it’s a whole battery field. As time passes, people can explore more parts of the periodic table” to find ever-better formulations, he says.
“This paper brings together innovative engineering advances in cell design and component materials within a strategic framework of ‘cost-based discovery’ that is amenable to the massive scale-up required of grid-scale applications,” says Richard Alkire, a professor of Chemical and Biomolecular Engineering at the University of Illinois, who was not involved in this research.
Because this work builds on a base of well-developed electrochemical systems used for aluminum production, Alkire says, “the path forward to grid-scale applications can therefore take advantage of a large body of existing engineering experience in areas of sustainability, environmental, life cycle, materials, manufacturing cost, and scale-up.”
The research was supported by the U.S. Department of Energy’s Advanced Research Projects Energy (ARPA-E) and by the French energy company Total S.A.
A team at the HZB Institute for Solar Fuels has developed a process for providing sensitive semiconductors for solar water splitting (“artificial leaves”) with an organic, transparent protective layer. The extremely thin protective layer made of carbon chains is stable, conductive, and covered with catalysing nanoparticles of metal oxides. These accelerate the splitting of water when irradiated by light. The team was able to produce a hybrid silicon-based photoanode structure that evolves oxygen at current densities above 15 mA/cm2. The results have now been published in Advanced Energy Materials.
The “artificial leaf” consists in principle of a solar cell that is combined with further functional layers. These act as electrodes and additionally are coated with catalysts. If the complex system of materials is submerged in water and illuminated, it can decompose water molecules. This causes hydrogen to be generated that stores solar energy in chemical form. However, there are still several problems with the current state of technology. For one thing, sufficient light must reach the solar cell in order to create the voltage for water splitting — despite the additional layers of material. Moreover, the semiconductor materials that the solar cells are generally made of are unable to withstand the typical acidic conditions for very long. For this reason, the artificial leaf needs a stable protective layer that must be simultaneously transparent and conductive.
Catalyst used twice
The team worked with samples of silicon, an n-doped semiconductor material that acts as a simple solar cell to produce a voltage when illuminated. Materials scientist Anahita Azarpira, a doctoral student in Dr. Thomas Schedel-Niedrig’s group, prepared these samples in such a way that carbon-hydrogen chains on the surface of the silicon were formed. “As a next step, I deposited nanoparticles of ruthenium dioxide, a catalyst,” Azarpira explains. This resulted in formation of a conductive and stable polymeric layer only three to four nanometres thick. The reactions in the electrochemical prototype cell were extremely complicated and could only be understood now at HZB.
The ruthenium dioxide particles in this new process were being used twice for the first time. In the first place, they provide for the development of an effective organic protective layer. This enables the process for producing protective layers — normally very complicated — to be greatly simplified. Only then does the catalyst do its “normal job” of accelerating the partitioning of water into oxygen and hydrogen.
Organic protection layer combines excellent stability with high current densities
The silicon electrode protected with this layer achieves current densities in excess of 15 mA/cm2. This indicates that the protection layer shows good electronic conductivity, which is by no means trivial for an organic layer. In addition, the researchers observed no degradation of the cell — the yield remained constant over the entire 24-hour measurement period. It is remarkable that an entirely different material has been favoured as an organic protective layer: graphene. This two-dimensional material has been the subject of much discussion, yet up to now could only be employed for electrochemical processes with limited success, while the protective layer developed at HZB works quite wel . Because the novel material could lend itself for the deposition process as well as for other applications, we are trying to acquire international protected property rights,” says Thomas Schedel-Niedrig, head of the group.
The above post is reprinted from materials provided by Helmholtz-Zentrum Berlin für Materialien und Energie. Note: Materials may be edited for content and length.
- Anahita Azarpira, Thomas Schedel-Niedrig, H.-J. Lewerenz, Michael Lublow. Sustained Water Oxidation by Direct Electrosynthesis of Ultrathin Organic Protection Films on Silicon. Advanced Energy Materials, 2016; DOI: 10.1002/aenm.201502314
25 Mar 2016
“This microbial nanowire is made of but a single peptide subunit,” said Gemma Reguera, lead author and MSU microbiologist. “Being made of protein, these organic nanowires are biodegradable and biocompatible. This discovery thus opens many applications in nanoelectronics such as the development of medical sensors and electronic devices that can be interfaced with human tissues.”
Since existing nanotechnologies incorporate exotic metals into their designs, the cost of organic nanowires is much more cost effective as well, she added.
How the nanowires function in nature is comparable to breathing. Bacterial cells, like humans, have to breathe. The process of respiration involves moving electrons out of an organism. Geobacter bacteria use the protein nanowires to bind and breathe metal-containing minerals such as iron oxides and soluble toxic metals such as uranium. The toxins are mineralized on the nanowires’ surface, preventing the metals from permeating the cell.
Reguera’s team purified their protein fibers, which are about 2 nanometers in diameter. Using the same toolset of nanotechnologists, the scientists were able to measure the high velocities at which the proteins were passing electrons.
“They are like power lines at the nanoscale,” Reguera said. “This also is the first study to show the ability of electrons to travel such long distances — more than a 1,000 times what’s been previously proven — along proteins.”
The researchers also identified metal traps on the surface of the protein nanowires that bind uranium with great affinity and could potentially trap other metals. These findings could provide the basis for systems that integrate protein nanowires to mine gold and other precious metals, scrubbers that can be deployed to immobilize uranium at remediation sites and more.
Reguera’s nanowires also can be modified to seek out other materials in which to help them breathe.
“The Geobacter cells are making these protein fibers naturally to breathe certain metals. We can use genetic engineering to tune the electronic and biochemical properties of the nanowires and enable new functionalities. We also can mimic the natural manufacturing process in the lab to mass-produce them in inexpensive and environmentally friendly processes,” Reguera said. “This contrasts dramatically with the manufacturing of humanmade inorganic nanowires, which involve high temperatures, toxic solvents, vacuums and specialized equipment.”
This discovery came from truly listening to bacteria, Reguera said.
“The protein is getting the credit, but we can’t forget to thank the bacteria that invented this,” she said. “It’s always wise to go back and ask bacteria what else they can teach us. In a way, we are eavesdropping on microbial conversations. It’s like listening to our elders, learning from their wisdom and taking it further.”
- Sanela Lampa-Pastirk, Joshua P. Veazey, Kathleen A. Walsh, Gustavo T. Feliciano, Rebecca J. Steidl, Stuart H. Tessmer, Gemma Reguera. Thermally activated charge transport in microbial protein nanowires. Scientific Reports, 2016; 6: 23517 DOI: 10.1038/srep23517