Iski E.V.,Center for Nanoscale Materials |
Yitamben E.N.,Center for Nanoscale Materials |
Gao L.,California State University, Northridge |
Guisinger N.P.,Argonne National Laboratory
Advanced Functional Materials | Year: 2013
Graphene is nature's ideal two-dimensional conductor and is comprised of a single sheet of hexagonally packed carbon atoms. Since the first electrical measurements made on graphene, researchers have been trying to exploit the unique properties of this material for a variety of applications that span numerous scientific and engineering disciplines. In order to fully realize the potential of graphene, large scale synthesis of high quality graphene and the ability to control the electronic properties of this material on a nanometer length-scale are necessary and remain key challenges. This article will review the efforts at the Center for Nanoscale Materials that focus on the atomic-scale characterization and modification of graphene via scanning tunneling microscopy and its synthesis on various materials (SiC, Cu(111), Cu foil, etc.). These fundamental studies explore growth dynamics, film quality, and the role of defects. The chemical modification of graphene following exposure to atomic hydrogen will also be covered, while additional emphasis will be made on graphene's unique structural properties. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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.
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's) 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 (Li O ), 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 (LiO ) 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 says. "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 explain, 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 says. Curtiss and Lu attribute 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 says. "However, this is just an intermediate step," Lu adds. "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 this week’s issue of Nature. The work was funded by the DOE's Office of Energy Efficiency and Renewable Energy and Office of Science.
« DOE BETO seeking input on Optima initiative for co-optimization of fuels and engines | Main | Volkswagen of America retains Ken Feinberg to design and administer claims program for TDI emissions compliance issue » A team of scientists from the US Department of Energy’s (DOE) Argonne National Laboratory, Northwestern University and Stony Brook University has, for the first time, synthesized a two-dimensional sheet of boron—borophene—by depositing elemental boron onto a silver surface under ultra-high vacuum conditions. Borophene is a honeycomb of boron atoms, with each hexagon capped by another boron atom. The study is published in Science. Scientists have been interested in two-dimensional materials for their unique characteristics, particularly involving their electronic properties. Borophene is an unusual material because it shows many metallic properties at the nanoscale even though three-dimensional, or bulk, boron is nonmetallic and semiconducting. Because borophene is both metallic and atomically thin, it holds promise for possible applications ranging from electronics to photovoltaics, said Argonne nanoscientist Nathan Guisinger, who led the experiment. “No bulk form of elemental boron has this metal-like behavior,” he said. Like its periodic table neighbor carbon, boron has a number of allotropes (different forms of the same element). But while graphite is composed of stacks of two-dimensional sheets that can be peeled off one at a time, there is no such analogous process for making two-dimensional boron. Although at least 16 bulk allotropes of boron are known, scientists had never before been able to make a whole sheet, or monolayer, of borophene. One of boron’s most unusual features consists of its atomic configuration at the nanoscale. While other two-dimensional materials look more or less like perfectly smooth and even planes at the nanoscale, borophene looks like corrugated cardboard, buckling up and down depending on how the boron atoms bind to one another, according to Andrew Mannix, a Northwestern graduate student and first author of the study. The “ridges” of this cardboard-like structure result in a material phenomenon known as anisotropy, in which a material’s mechanical or electronic properties—such as its electrical conductivity—become directionally dependent. “This extreme anisotropy is rare in two-dimensional materials and has not been seen before in a two-dimensional metal,” Mannix said. Based on theoretical predictions of borophene’s characteristics, the researchers also noticed that it likely has a higher tensile strength than any other known material. The discovery and synthesis of borophene was aided by computer simulation work led by Stony Brook researchers Xiang-Feng Zhou and Artem Oganov, who is currently affiliated with the Moscow Institute of Physics and Technology and the Skolkovo Institute of Science and Technology. Oganov and Zhou used advanced simulation methods that showed the formation of the crinkles of the corrugated surface. The experimental work was funded by the DOE’s Office of Science and was performed at Argonne’s Center for Nanoscale Materials, a DOE Office of Science user facility, and at the Northwestern University Materials Research Center.
« BMW using Hexcel CFRP in 7 Series B-pillar | Main | Zhejiang VIE Science and Technology leads US$10M Series B for wireless charging company Evatran » Researchers from Argonne National Laboratory, with colleagues in the US and Korea, have demonstrated a lithium-oxygen battery based on lithium superoxide (LiO ). The work, reported in the journal Nature, could open the way to very high-energy-density batteries based on LiO as well as to other possible uses of the compound, such as oxygen storage. Lithium-air batteries form lithium peroxide (Li O )—a solid precipitate that clogs the pores of the electrode and degrades cell performance—as part of the charge−discharge reaction process. This remains a core challenge that needs to be overcome for the viable commercialization of Li-air technology. However, a number of studies of Li–air batteries have found evidence of LiO being formed as one component of the discharge product along with lithium peroxide (Li O ). Unlike lithium peroxide, lithium superoxide can easily dissociate into lithium and oxygen, leading to high efficiency and good cycle life. In addition, theoretical calculations have indicated that some forms of LiO may have a long lifetime. Here we show that crystalline LiO can be stabilized in a Li–O battery by using a suitable graphene-based cathode. Various characterization techniques reveal no evidence for the presence of Li O . A novel templating growth mechanism involving the use of iridium nanoparticles on the cathode surface may be responsible for the growth of crystalline LiO . Our results demonstrate that the LiO formed in the Li–O battery is stable enough for the battery to be repeatedly charged and discharged with a very low charge potential (about 3.2 volts). The major advantage of a battery based on lithium superoxide, Argonne battery scientists Larry Curtiss and Khalil Amine explained, is that it allows, at least in theory, for the creation of a lithium-air battery that consists of 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 researchers attributed the growth of the lithium superoxide to the spacing of iridium atoms in the electrode used in the experiment. 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. The work was funded by the DOE’s Office of Energy Efficiency and Renewable Energy and Office of Science.