Pasquale F. Fulvio

Carbon Materials for Chemical Capacitive Energy Storage

Carbon materials have attracted intense interests as electrode materials for electrochemical capacitors, because of their high surface area, electrical conductivity, chemical stability and low cost. Activated carbons produced by different activation processes from various precursors are the most widely used electrodes. Recently, with the rapid growth of nanotechnology, nanostructured electrode materials, such as carbon nanotubes and template-synthesized porous carbons have been developed. Their unique electrical properties and well controlled pore sizes and structures facilitate fast ion and electron transportation. In order to further improve the power and energy densities of the capacitors, carbon-based composites combining electrical double layer capacitors (EDLC)-capacitance and pseudo-capacitance have been explored. They show not only enhanced capacitance, but as well good cyclability. In this review, recent progresses on carbon-based electrode materials are summarized, including activated carbons, carbon nanotubes, and template-synthesized porous carbons, in particular mesoporous carbons. Their advantages and disadvantages as electrochemical capacitors are discussed. At the end of this review, the future trends of electrochemical capacitors with high energy and power are proposed.

Role of hydrogen in chemical vapor deposition growth of large single-crystal graphene.

We show that graphene chemical vapor deposition growth on copper foil using methane as a carbon source is strongly affected by hydrogen, which appears to serve a dual role: an activator of the surface bound carbon that is necessary for monolayer growth and an etching reagent that controls the size and morphology of the graphene domains. The resulting growth rate for a fixed methane partial pressure has a maximum at hydrogen partial pressures 200-400 times that of methane. The morphology and size of the graphene domains, as well as the number of layers, change with hydrogen pressure from irregularly shaped incomplete bilayers to well-defined perfect single layer hexagons. Raman spectra suggest the zigzag termination in the hexagons as more stable than the armchair edges.

Soft‐Templated Mesoporous Carbon‐Carbon Nanotube Composites for High Performance Lithium‐ion Batteries

Mesoporous carbon with homogeneously dispersed multi-walled carbon nanotubes (MWNTs) are synthesized via a one-step brick and mortar soft-templating approach. Nanocomposites exhibit high rate capability and reversible lithium storage capacity of 900 mA h g-1 and good rate performance. Such homogeneous nanocomposites are ideal candidates for electric vehicle applications where high power and energy density are primary requirements.

Ordered Mesoporous Alumina-Supported Metal Oxides

The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.

Direct exfoliation of natural graphite into micrometre size few layers graphene sheets using ionic liquids

Stable high-concentration suspensions (up to 0.95 mg mL(-1)) of non-oxidized few layer graphene (FLG), five or less sheets, with micrometre-long edges were obtained via direct exfoliation of natural graphite flakes in ionic liquids, such as 1-butyl-3-methyl-imidazolium bis(trifluoro-methane-sulfonyl)imide ([Bmim]-[Tf(2)N]), by tip ultrasonication.

Seawater Uranium Sorbents: Preparation from a Mesoporous Copolymer Initiator by Atom-Transfer Radical Polymerization†

The world s oceans, where uranium is found quite uniformly at a concentration of 3.3 mgL , present an alternative source of uranium to terrestrial mining for nuclear fuel. Environmental concerns associated with mining will undoubtedly increase as reserves are depleted, thus increasing the utility of more environmentally friendly feedstocks. Hence, before terrestrial resources become scarce, the development of sorbents designed for seawater extraction is of strategic importance to guarantee future uranium resources. From the first inorganic adsorbents, which showed poor selectivity and mechanical resistance, to the most recent polyethylene-fiberbased sorbents containing amidoxime–carboxylic acid copolymers, and more recently layered metal sulfides and metal– organic frameworks, interest in uranium seawater extractions has continuously increased among governments worldwide. Because the concentration of uranium in the oceans is relatively low, maximization of the adsorption properties of sorbents, for example, through changes in their surface area and pore structure, can greatly improve the kinetics of uranium extraction and the adsorption capacity simultaneously. To facilitate the uptake of uranyl ions with fast kinetics, various sorbents containing the amidoxime group, such as hydrogels, particles and beads, membranes, macroporous fibers, and composites, have been prepared by suspension polymerization, radiation-induced grafting, and even sonochemical functionalization. However, silica beads and most carbon materials have a relatively small accessible surface area for the growth of large polymers or a low number of surface sites available for the grafting of functional groups. Thus, the design of substrates with large numbers of accessible reactive sites for the grafting of polymeric surface groups is necessary for the development of materials with improved uranium-adsorption capacity. Recently, porous polymers based on divinylbenzene (DVB) have been developed for applications in separations and catalysis. For example, the copolymerization of p-styrene sulfonate with divinylbenzene led to a catalytically active porous polymer. This method has the additional advantage that polymers can be obtained with controlled porosity and high surface areas without porogens. It is thus timeand cost-effective, as well as more environmentally friendly than the templated synthesis of carbonaceous materials. Motivated by these findings, we report herein nanoporous polymers based on the vinylbenzyl chloride (VBC) monomer and the DVB cross-linking agent. As well as a well-developed nanoporous structure of microand mesopores, the obtained polymers contain large numbers of accessible chlorine species, which can be used as initiators for atom-transfer radical polymerization (ATRP). These materials are the first examples of ATRP initiators in which the initiator species is located within the framework of the mesoporous support. The accessible framework and surface chlorine species were used to grow polyacrylonitrile chains, which were then converted into polyamidoxime for uranium adsorption from seawater with tailorable adsorption and surface properties. Three copolymer monoliths were synthesized by freeradical polymerization; that is, the monomer 4-vinylbenzyl chloride was cross-linked by divinylbenzene with 2,2’-azobisisobutyronitrile (AIBN, 98%) as the initiator to give copolymers hereafter referred to as p(xDVB-VBC) (in which x stands for the molar ratio of DVB to VBC). By varying the ratio of the monomer and the cross-linking reactant, it was possible to adjust the pore structure, that is, the surface area and pore volume (Figure 1). Since these adjustments arose from changes in the DVB to VBC ratio, the initiator concentration (i.e. the amount of chloride substituents present) was also varied. The nitrogen isotherms measured at 196 8C for the samples show that nonporous materials as well as materials with tailorable mesopore volumes can be [*] Dr. Y. Yue, Dr. R. T. Mayes, Dr. P. F. Fulvio, Dr. X.-G. Sun, Prof. Dr. S. Dai Chemical Sciences Division, Oak Ridge National Laboratory Oak Ridge, TN 37831 (USA) E-mail: dais@ornl.gov

Nanoscale Perturbations of Room Temperature Ionic Liquid Structure at Charged and Uncharged Interfaces

The nanoscale interactions of room temperature ionic liquids (RTILs) at uncharged (graphene) and charged (muscovite mica) solid surfaces were evaluated with high resolution X-ray interface scattering and fully atomistic molecular dynamics simulations. At uncharged graphene surfaces, the imidazolium-based RTIL ([bmim(+)][Tf(2)N(-)]) exhibits a mixed cation/anion layering with a strong interfacial densification of the first RTIL layer. The first layer density observed via experiment is larger than that predicted by simulation and the apparent discrepancy can be understood with the inclusion of, dominantly, image charge and π-stacking interactions between the RTIL and the graphene sheet. In contrast, the RTIL structure adjacent to the charged mica surface exhibits an alternating cation-anion layering extending 3.5 nm into the bulk fluid. The associated charge density profile demonstrates a pronounced charge overscreening (i.e., excess first-layer counterions with respect to the adjacent surface charge), highlighting the critical role of charge-induced nanoscale correlations of the RTIL. These observations confirm key aspects of a predicted electric double layer structure from an analytical Landau-Ginzburg-type continuum theory incorporating ion correlation effects, and provide a new baseline for understanding the fundamental nanoscale response of RTILs at charged interfaces.

Electrical and thermal conductivity of low temperature CVD graphene: the effect of disorder

In this paper we present a study of graphene produced by chemical vapor deposition (CVD) under different conditions with the main emphasis on correlating the thermal and electrical properties with the degree of disorder. Graphene grown by CVD on Cu and Ni catalysts demonstrates the increasing extent of disorder at low deposition temperatures as revealed by the Raman peak ratio, IG/ID. We relate this ratio to the characteristic domain size, La, and investigate the electrical and thermal conductivity of graphene as a function of La. The electrical resistivity, ρ, measured on graphene samples transferred onto SiO2/Si substrates shows linear correlation with La(-1). The thermal conductivity, K, measured on the same graphene samples suspended on silicon pillars, on the other hand, appears to have a much weaker dependence on La, close to K∼La1/3. It results in an apparent ρ∼K3 correlation between them. Despite the progressively increasing structural disorder in graphene grown at lower temperatures, it shows remarkably high thermal conductivity (10(2)-10(3) W K(-1) m(-1)) and low electrical (10(3)-3×10(5) Ω) resistivities suitable for various applications.

Tailoring properties of SBA-15 materials by controlling conditions of hydrothermal synthesis

The influence of synthesis time and temperature on the properties of SBA-15 is investigated for the samples prepared by using two different silica sources, tetraethylorthosilicate (TEOS) and sodium metasilicate. The samples studied were obtained via two-step synthesis, which involved an initial self-assembly of polymer and silica species at 40 °C for 2 hours followed by longer hydrothermal treatment at higher temperatures. The SBA-15 samples obtained from both silica sources were highly ordered as evidenced by SAXS spectra showing up to seven reflection peaks characteristic of the P6mm symmetry group. While for the samples studied the specific surface area decreased with increasing time and temperature of the hydrothermal treatment, their mesopore size distributions became narrower and their mesopore widths and mesopore volumes showed a tendency to increase. In contrast, a slight decrease in the mesopore wall thickness and micropore volume was observed with increasing time of this treatment. Also, the samples obtained from sodium metasilicate exhibited thicker mesopore walls than those prepared from TEOS. It was shown that the adsorption properties of SBA-15 can be tailored by adjusting the time and temperature of the hydrothermal treatment and simultaneously reducing the time of the initial self-assembly process from 24 h to 2 h.

Template-Free Synthesis of Hierarchical Porous Metal-Organic Frameworks

A template-free synthesis of a hierarchical microporous-mesoporous metal-organic framework (MOF) of zinc(II) 2,5-dihydroxy-1,4-benzenedicarboxylate (Zn-MOF-74) is reported. The surface morphology and porosity of the bimodal materials can be modified by etching the pore walls with various synthesis solvents for different reaction times. This template-free strategy enables the preparation of stable frameworks with mesopores exceeding 15 nm, which was previously unattained in the synthesis of MOFs by the ligand-extension method.