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Truong T.T.,Center for Nanoscale Materials | Liu Y.,Center for Nanoscale Materials | Ren Y.,Advanced Photon Source | Trahey L.,Argonne National Laboratory | Sun Y.,Center for Nanoscale Materials
ACS Nano | Year: 2012

Single-crystal α-MnO 2 nanotubes have been successfully synthesized by microwave-assisted hydrothermal of potassium permanganate in the presence of hydrochloric acid. The growth mechanism including the morphological and crystalline evolution has been carefully studied with time-dependent X-ray diffraction, electron microscopy, and controlled synthesis. The as-synthesized MnO 2 nanostructures are incorporated in air cathodes of lithium-air batteries as electrocatalysts for the oxygen reduction and evolution reactions. The characterization reveals that the electrodes made of single-crystalline α-MnO 2 nanotubes exhibit much better stability than those made of α-MnO 2 nanowires and δ-MnO 2 nanosheet-based microflowers in both charge and discharge processes. © 2012 American Chemical Society. Source

News Article | August 22, 2016
Site: http://phys.org/chemistry-news/materials-science

In a new study, researchers from the Cambridge Crystallographic Data Centre (CCDC) and the U.S. Department of Energy's (DOE's) Argonne National Laboratory have teamed up to capture neon within a porous crystalline framework. Neon is well known for being the most unreactive element and is a key component in semiconductor manufacturing, but neon has never been studied within an organic or metal-organic framework until now. The results, which include the critical studies carried out at the Advanced Photon Source (APS), a DOE Office of Science user facility at Argonne, also point the way towards a more economical and greener industrial process for neon production.

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Site: http://www.nanotech-now.com/

Abstract: While lithium-ion batteries have transformed our everyday lives, researchers are currently trying to find new chemistries that could offer even better energy possibilities. One of these chemistries, lithium-air, could promise greater energy density but has certain drawbacks as well. Now, thanks to research at the U.S. Department of Energy's (DOE) Argonne National Laboratory, one of those drawbacks may have been overcome. All previous work on lithium-air batteries showed the same phenomenon: the formation of lithium peroxide (Li2O2), a solid precipitate that clogged the pores of the electrode. In a recent experiment, however, Argonne battery scientists Jun Lu, Larry Curtiss and Khalil Amine, along with American and Korean collaborators, were able to produce stable crystallized lithium superoxide ((LiO2) instead of lithium peroxide during battery discharging. Unlike lithium peroxide, lithium superoxide can easily dissociate into lithium and oxygen, leading to high efficiency and good cycle life. "This discovery really opens a pathway for the potential development of a new kind of battery," Curtiss said. "Although a lot more research is needed, the cycle life of the battery is what we were looking for." The major advantage of a battery based on lithium superoxide, Curtiss and Amine explained, is that it allows, at least in theory, for the creation of a lithium-air battery that consists of what chemists call a "closed system." Open systems require the consistent intake of extra oxygen from the environment, while closed systems do not - making them safer and more efficient. "The stabilization of the superoxide phase could lead to developing a new closed battery system based on lithium superoxide, which has the potential of offering truly five times the energy density of lithium ion," Amine said. Curtiss and Lu attributed the growth of the lithium superoxide to the spacing of iridium atoms in the electrode used in the experiment. "It looks like iridium will serve as a good template for the growth of superoxide," Curtiss said. "However, this is just an intermediate step," Lu added. "We have to learn how to design catalysts to understand exactly what's involved in lithium-air batteries." ### The researchers confirmed the lack of lithium peroxide by using X-ray diffraction provided by the Advanced Photon Source, a DOE Office of Science User Facility located at Argonne. They also received allocations of time on the Mira supercomputer at the Argonne Leadership Computing Facility, which is also a DOE Office of Science User Facility. The researchers also performed some of the work at Argonne's Center for Nanoscale Materials, which is also a DOE Office of Science User Facility. A study based on the research appeared in the January 11 issue of Nature. The work was funded by the DOE's Office of Energy Efficiency and Renewable Energy and Office of Science. About Argonne National Laboratory Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science. The U.S. Department of Energy'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. For more information, please visit the Office of Science website. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

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Site: http://www.rdmag.com/rss-feeds/all/rss.xml/all

FAYETTEVILLE, AR — An international group of physicists led by the University of Arkansas has created an artificial material with a structure comparable to graphene. “We’ve basically created the first artificial graphene-like structure with transition metal atoms in place of carbon atoms,” said Jak Chakhalian, professor of physics and director of the Artificial Quantum Materials Laboratory at the U of A. In 2014, Chakhalian was selected as a quantum materials investigator for the Gordon and Betty Moore Foundation. His selection came with a $1.8 million grant, a portion of which funded the study. Graphene, discovered in 2004, is a one-atom-thick sheet of graphite. Graphene transistors are predicted to be substantially faster and more heat-tolerant than today’s silicon transistors and may result in more efficient computers and the next-generation of flexible electronics. Its discoverers were awarded the Nobel Prize in physics in 2010. The U of A-led group published its findings this week in Physical Review Letters, the journal of the American Physical Society, in a paper titled “Mott Electrons in an Artificial Graphene-like Crystal of Rare Earth Nickelate.” “This discovery gives us the ability to create graphene-like structures for many other elements,” said Srimanta Middey, a postdoctoral research associate at the U of A who led the study. The research group also included U of A postdoctoral research associates Michael Kareev and Yanwei Cao, doctoral student Xiaoran Liu and recent doctoral graduate Derek Meyers, now at Brookhaven National Laboratory. Additional members of the group were David Doennig of the University of Munich, Rossitza Pentcheva of the University of Duisburg-Essen in Germany, Zhenzhong Yang, Jinan Shi and Lin Gu of the Chinese Academy of Sciences; and John W. Freeland and Phillip Ryan of the Advanced Photon Source at Argonne National Laboratory near Chicago. The research was also partially funded by the Chinese Academy of Sciences.

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Site: http://www.cemag.us/rss-feeds/all/rss.xml/all

Inexpensive materials called MOFs pull gases out of air or other mixed gas streams, but fail to do so with oxygen. Now, a team has overcome this limitation by creating a composite of a MOF and a helper molecule in which the two work in concert to separate oxygen from other gases simply and cheaply. The results, reported in Advanced Materials, might help with a wide variety of applications, including making pure oxygen for fuel cells, using that oxygen in a fuel cell, removing oxygen in food packaging, making oxygen sensors, or for other industrial processes. The technique might also be used with gases other than oxygen as well by switching out the helper molecule. Currently, industry uses a common process called cryogenic distillation to separate oxygen from other gases. It is costly and uses a lot of energy to chill gases. Also, it can't be used for specialty applications like sensors or getting the last bit of oxygen out of food packaging. A great oxygen separator would be easy to prepare and use, be inexpensive and be reusable. MOFs, or metal-organic frameworks, are materials containing lots of pores that can suck up gases like sponges suck up water. They have potential in nuclear fuel separation and in lightweight dehumidifiers. But of the thousands of MOFs out there, less than a handful absorb molecular oxygen. And those MOFs chemically react with oxygen, forming oxides — think rust — that render the material unusable. "When we first worked with MOFs for oxygen separation, we could only use the MOFs a few times. We thought maybe there's a better way to do it," says materials scientist Praveen Thallapally of the Department of Energy's Pacific Northwest National Laboratory. The new tack for Thallapally and colleagues at PNNL involved using a second molecule to mediate the oxygen separation — a helper molecule would be attracted to but chemically uninterested in the MOF. Instead, the helper would react with oxygen to separate it from other gases. They chose a MOF called MIL-101 that is known for its high surface area — making it a powerful sponge — and lack of reactivity. One teaspoon of MIL-101 has the same surface area as a football field. The high surface area comes from a MOF's pores, where reactive MOFs work their magic. MOFs that react with oxygen need to be handled carefully in the laboratory, but MIL-101 is stable at ambient temperatures and in the open atmosphere of a lab. For their helper molecule, they tried ferrocene, an inexpensive iron-containing molecule. The scientists made a composite of MIL-101 and ferrocene by mixing them and heating them up. Initial tests showed that MIL-101 took up more than its weight in ferrocene and at the same time lost surface area. This indicated that ferrocene was taking up space within the MOF's pores, where they need to be to snag the oxygen. Then the team sent gases through the black composite material. The material bound up a large percentage of oxygen, but almost none of the added nitrogen, argon or carbon dioxide. The material behaved this way whether the gases went through individually or as a mix, showing that the composite could in fact separate oxygen from the others. Additional analysis showed that heating caused ferrocene to decompose in the pores to nanometer-sized clusters, which made iron available to react with oxygen. This reaction formed a stable mineral known as maghemite, all within the MOF pores. Maghemite could be removed from the MOF to use the MOF again. Together, the results on the composite showed that a MOF might be able to do unexpected things — like purify oxygen — with a little help. Future research will explore other combinations of MOF and helper molecules. In addition to PNNL, participating researchers hailed from and used analytical instruments at two Office of Science User Facilities, the Environmental Molecular Sciences Laboratory at PNNL and the Advanced Photon Source at Argonne National Laboratory, as well as the University of Amsterdam. This work was supported by the Department of Energy Office of Science.

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