The intrinsic electrocatalytic properties of functionalized graphene sheets (FGSs) in nitric oxide (NO) sensing are determined by cyclic voltammetry with FGS monolayer electrodes. The degrees of reduction and defectiveness of the FGSs are varied by employing different heat treatments during their fabrication. FGSs with intermediate degrees of reduction and high Raman I-D to I-G peak ratios exhibit an NO oxidation peak potential of 794 mV (vs 1 M Ag/AgCl), closely matching values obtained with a platinized Pt control (791 mV) as well as recent results from the literature on porous or biofunctionalized electrodes. We show that the peak potential obtained with FGS electrodes can be further reduced to 764 mV by incorporation of electrode porosity using a drop-casting approach, indicating a stronger apparent electrocatalytic effect on porous FGS electrodes as compared to platinized Pt. Taking into consideration effects of electrode Morphology, we thereby demonstrate that FGSs are intrinsically as catalytic toward NO oxidation as platinum. The lowered peak potential of porous FGS electrodes is accompanied by a significant increase in peak current, which we attribute either to pore depletion effects or an amplification effect due to subsequent electrooxidation reactions. Our results suggest that the development of sensor electrodes with higher sensitivity and lower detection limits should be feasible with FGSs.

We use colloidal gels of graphene oxide in a water-ethanol-ionic liquid solution to assemble graphene-ionic liquid laminated structures for use as electrodes in electrochemical double layer capacitors. Our process involves evaporation of water and ethanol yielding a graphene oxide/ionic liquid composite, followed by thermal reduction of the graphene oxide to electrically conducting functionalized graphene. This yields an electrode in which the ionic liquid serves not only as the working electrolyte but also as a spacer to separate the graphene sheets and to increase their electrolyte-accessible surface area. Using this approach, we achieve an outstanding energy density of 17.5 Wh/kg at a gravimetric capacitance of 156 F/g and 3 V operating voltage, due to a high effective density of the active electrode material of 0.46 g/cm(2). By increasing the ionic liquid content and the degree of thermal reduction, we obtain electrodes that retain >90% of their capacitance at a scan rate of 500 mV/s, illustrating that we can tailor the electrodes toward higher power density if energy density is not the primary goal. The elimination of the electrolyte infiltration step from manufacturing makes,this bottom-up assembly approach scalable and well-suited for combinations of potentially any graphene material with ionic liquid electrolytes. (C) 2013 The Electrochemical Society. All rights reserved.

We report on the adsorption of sodium dodecyl sulfate (SDS) onto functionalized graphene sheets (FGSs) in an aqueous system, measured at broad SDS and FGS concentration ranges by conductometric surfactant titration. At dilute SDS concentrations (<12 mu M in bulk solution), there is evidence of a counterion exchange between hydronium ions (from the dissociation of acidic chemical functionalities on FGS) and sodium ions coadsorbing with dodecyl sulfate monomers onto FGSs. We find that, for FGS with a carbon-to-oxygen ratio of similar to 18, monolayer adsorption of SDS on FGS reaches full surface coverage by similar to 12 mu M SDS. Additionally, the critical surface aggregation concentration (csac) for surface micelle formation on FGS is measured to be similar to 1.5 mM SDS The transition from monolayer adsorption to surface micelle formation appears to occur at a similar SDS concentration on FGSs as on graphite, suggesting there is little difference in the surfactant adsorption behavior on both materials. We estimate that the FGS surface area available for SDS adsorption is similar to 600 m(2)/g which is significantly less than expected for FGSs in suspension and indicates the presence of regions on FGS on which SDS adsorption does not occur.

We have studied the processes leading to the cementation of colloidal particles during their autonomous assembly on corroding copper electrodes within a Cu-Au galvanic rnicroreactor. We determined the onset of particle immobilization through particle tracking, monitored the dissolution of copper as well as the deposition of insoluble products of the corrosion reactions in situ, and showed that particle immobilization initiated after reaction products (RPs) began to deposit on the electrode substrate. We further demonstrated that the time and the extent of RP precipitation and thus the strength of the particle-substrate bond could be tuned by varying the amount of copper in the system and the microreactor pH. The ability to cement colloidal particles at locations undergoing corrosion illustrates that the studied colloidal assembly approach holds potential for applications in dynamic material property adaptation.

The mechanisms leading to the deposition of colloidal particles in a copper-gold galvanic microreactor are investigated. Using in situ current density measurements and particle velocimetry, we establish correlations between the spatial arrangement and the geometry of the electrodes, current density distribution, and particle aggregation behavior. Ionic transport phenomena are responsible for the occurrence of strongly localized high current density at the edges and corners of the copper electrodes at large electrode separation, leading to a preferential aggregation of colloidal particles at the electrode edges. Preferential aggregation appears to be the result of a combination of electrophoretic effects and changes in bulk electrolyte flow patterns. We demonstrate that electrolyte flow is most likely driven by electrochemical potential gradients of reaction products formed during the inhomogeneous copper dissolution.

A separation medium, such as a chromatography filling or packing, containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m²/g to 2600 m²/g, wherein the thermally exfoliated graphite oxide has a surface that has been at least partially functionalized.

A gas diffusion barrier contains a polymer matrix and a functional graphene which displays no signature of graphite and/or graphite oxide, as determined by X-ray diffraction.

A gas storage cylinder or gas storage cylinder liner, formed from a polymer composite, containing at least one polymer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m²/g to 2600 m²/g.

A supercapacitor or battery electrode containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m²/g to 2600 m²/g.

Nanocomposite materials comprising a metal oxide bonded to at least one graphene material. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10C.

Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an elec. conductive ink comprising functionalized graphene sheets and at least one binder. A method of prepg. printed electronic devices is further disclosed.

We report on a technique that utilizes an array of galvanic microreactors to guide the assembly of two-dimensional colloidal crystals with spatial and orientational order. Our system is comprised of an array of copper and gold electrodes in a coplanar arrangement, immersed in a dilute hydrochloric acid solution in which colloidal micro-spheres of polystyrene and silica are suspended. Under optimized conditions, two-dimensional colloidal crystals form at the anodic copper with patterns and crystal orientation governed by the electrode geometry. After the aggregation process, the colloidal particles are cemented to the substrate by co-deposition of reaction products. As we vary the electrode geometry, the dissolution rate of the copper electrodes is altered. This way, we control the colloidal motion as well as the degree of reaction product formation. We show that particle motion is governed by a combination of electrokinetic effects acting directly on the colloidal particles and bulk electrolyte flow generated at the copper-gold interface. (C) 2012 American Institute of Physics.

For many applications of dielectric elastomer actuators, it is desirable to replace the carbon-grease electrodes with stretchable, solid-state electrodes. Here, we attach thin layers of a conducting silicone elastomer to prestrained films of an acrylic dielectric elastomer and achieve voltage-actuated areal strains over 70%. The influence of the stiffness of the electrodes and the prestrain of the dielectric films is studied experimentally and theoretically. (C) 2012 American Institute of Physics.

The burning rate of the monopropellant nitromethane (NM) has been observed to increase by adding and dispersing small amounts of functionalized graphene sheets (FGSs) in liquid NM. Until now, no plausible mechanisms for FGSs acting as combustion catalysts have been presented. Here, we report ab initio molecular dynamics simulations showing that carbon vacancy defects within the plane of the FGSs, fimctionalized with oxygen-containing groups, greatly accelerate the thermal decomposition of NM and its derivatives. This occurs through reaction pathways involving the exchange of protons or oxygens between the oxygen-containing functional groups and NM and its derivatives. FGS initiates and promotes the decomposition of the monopropellant and its derivatives, ultimately forming H2O, CO2, and N-2. Concomitantly, oxygen-containing functional groups on the FGSs are consumed and regenerated without significantly changing the FGSs in accordance with experiments indicating that the FGSs are not consumed during combustion.

Several techniques for fabricating functionalized graphene sheet (FGS) electrodes were tested for catalytic performance in dye-sensitized solar cells (DSSCs). By using ethyl cellulose as a sacrificial binder, and partially thermolyzing it, we were able to create electrodes which exhibited lower effective charge transfer resistance (<1 Omega cm(2)) than the thermally decomposed chloroplatinic acid electrodes traditionally used. This performance was achieved not only for the triiodide/iodide redox couple, but also for the two other major redox mediators used in DSSCs, based on cobalt and sulfur complexes, showing the versatility of the electrode. DSSCs using these FGS electrodes had efficiencies (eta) equal to or higher than those using thermally decomposed chloroplatinic acid electrodes in each of the three major redox mediators: I (eta(FGS) = 6.8%, eta(Pt) = 6.8%), Co (4.5%, 4.4%), S (3.5%, 2.0%). Through an analysis of the thermolysis of the binder and composite material, we determined that the high surface area of an electrode, as determined by nitrogen adsorption, is consistent with but not sufficient for high performing electrodes. Two other important considerations are that (i) enough residue remains in the composite to maintain structural stability and prevent restacking of FGSs upon the introduction of the solvent, and (ii) this residue must not disperse in the electrolyte.

We summarize our recent studies on the use of low-density nanoporous silica structures prepared through templating of a self-assembling disordered liquid-crystalline L (3) phase, as a matrix for use in numerous applications, including sensing, optical data storage, drug release, and structural. The silica matrix exhibits low density (0.5 g cm(-3) to 0.8 g cm(-3) for monoliths, 0.6 g cm(-3) to 0.99 g cm(-3) for fibers) coupled with high surface areas (up 1400 m(2) g(-1)) and void volumes (65% or higher). High-surface-area coatings are used to increase the sensitivity of mass-detecting quartz crystal microbalances to over 4000 times that of uncoated crystals. Monoliths, films, and fibers are produced using the templated silica gel. Once dried and converted to silica, the nanostructured material exhibits high fracture strength (up to 35 MPa in fibers) and Young's modulus (30 GPa to 40 GPa in fibers). These values are, respectively, two orders of magnitude and twice those of nanostructured silicas having comparable densities.

We demonstrate the use of functionalized graphene sheets (FGSs) as multifunctional nanofillers to improve mechanical properties, lower gas permeability, and impart electrical conductivity for several distinct elastomers. FGS consists mainly of single sheets of crumbled graphene containing oxygen functional groups and is produced by the thermal exfoliation of oxidized graphite (GO). The present investigation includes composites of FGS and three elastomers: natural rubber (NR), styrenebutadiene rubber, and polydimethylsiloxane (PDMS). All of these elastomers show similar and significant improvements in mechanical properties with FGS, indicating that the mechanism of property improvement is inherent to the FGS and not simply a function of chemical crosslinking. The decrease in gas permeability is attributed to the high aspect ratio of the FGS sheets. This creates a tortuous path mechanism of gas diffusion; fitting the permeability data to the Nielsen model yields an aspect ratio of similar to 1000 for the FGS. Electrical conductivity is demonstrated at FGS loadings as low as 0.08% in PDMS and reaches 0.3 S/m at 4 wt % loading in NR. This combination of functionalities imparted by FGS is shown to result from its high aspect ratio and carbon-based structure. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

The effects of functionalized graphene sheets (FGSs) on the mechanical properties and strain-induced crystallization of natural rubber (NR) are investigated. FGSs are predominantly single sheets of graphene with a lateral size of several hundreds of nanometers and a thickness of 1.5 nm. The effect of FGS and that of carbon black (CB) on the strain-induced crystallization of NR is compared by coupled tensile tests and X-ray diffraction experiments. Synchrotron X-ray scattering enables simultaneous measurements of stress and crystallization of NR in real time during sample stretching. The onset of crystallization occurs at significantly lower strains for FGS-filled NR samples compared with CB-filled NR, even at low loadings. Neat-NR exhibits strain-induced crystallization around a strain of 2.25, while incorporation of 1 and 4 wt % FGS shifts the crystallization to strains of 1.25 and 0.75, respectively. In contrast, loadings of 16 wt % CB do not significantly shift the critical strain for crystallization. Two-dimensional (2D) wide angle X-ray scattering patterns show minor polymer chain alignment during stretching, in accord with previous results for NR. Small angle X-ray scattering shows that FGS is aligned in the stretching direction, whereas CB does not show alignment or anisotropy. The mechanical properties of filled NR samples are investigated using cyclic tensile and dynamic mechanical measurements above and below the glass transition of NR. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochem. or energy storage device. [on SciFinder(R)]

Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochem. or energy storage device. [on SciFinder(R)]

The invention refers to a high surface area scaffold to be used for a solar cell, made of a three-dimensional percolated network of functionalized graphene sheets. It may be used in the prepn. of a high surface area electrode by coating with a semiconductive material. Electronic devices can be made therefrom, including solar cells such as dye-sensitized solar cells. [on SciFinder(R)]

We have studied the effect of the oxidation path and the mechanical energy input on the size of graphene oxide sheets derived from graphite oxide. The cross-planar oxidation of graphite from the (0002) plane results in periodic cracking of the uppermost graphene oxide layer, limiting its lateral dimension to less than 30 mu m. We use an energy balance between the elastic strain energy associated with the undulation of graphene oxide sheets at the hydroxyl and epoxy sites, the crack formation energy, and the interaction energy between graphene layers to determine the cell size of the cracks. As the effective crack propagation rate in the cross-planar direction is an order of magnitude smaller than the edge-to-center oxidation rate, graphene oxide single sheets larger than those defined by the periodic cracking cell size are produced depending on the aspect ratio of the graphite particles. We also demonstrate that external energy input from hydrodynamic drag created by fluid motion or sonication, further reduces the size of the graphene oxide sheets through tensile stress buildup in the sheets.

Perchlorate (ClO4-) contamination is a widespread concern affecting water utilities. In the present study, functionalized graphene sheets were employed as the scaffold to synthesize a novel graphene-polypyrrole (Ppy) nanocomposite, which served as an excellent electrically switched ion exchanger for perchlorate removal. Scanning electron microscopy and electrochemical measurements showed that the 3D nanostructured graphene-Ppy nanocomposite exhibited a significantly improved uptake capacity for ClO4- compared with Ppy film alone. X-ray photoelectron spectroscopy confirmed the uptake and release process of ClO4- in graphene-Ppy nanocomposite. In addition, the presence of graphene substrate resulted in high stability of graphene-Ppy nanocomposite during potential cycling. The present work provides a promising method for large scale water treatment.

The lithium-ir battery is one of the most promising technologies among various electrochemical energy storage systems. We demonstrate that a novel air electrode consisting of an unusual hierarchical arrangement of functionalized graphene sheets (with no catalyst) delivers an exceptionally high capacity of 15000 mAh/g in lithium-O-2 batteries which is the highest value ever reported in this field. This excellent performance is attributed to the unique bimodal porous structure of the electrode which consists of microporous channels facilitating rapid O-2 diffusion while the highly connected nanoscale pores provide a high density of reactive sites for Li-O-2 reactions. Further, we show that the defects and functional groups on graphene favor the formation of isolated nanosized Li2O2 particles and help prevent air blocking in the air electrode. The hierarchically ordered porous structure in bulk graphene enables its practical applications by promoting accessibility to most graphene sheets in this structure.

We describe a scalable method for producing continuous graphene networks by tape casting surfactant-stabilized aqueous suspensions of functionalized graphene sheets. Similar to all other highly connected graphene-containing networks, the degree of overlap between the sheets controls the tapes' electrical and mechanical properties. However, unlike other graphene-containing networks, the specific surface area of the cast tapes remains high (>400 m(2).g(-1)). Exhibiting apparent densities between 0.15 and 0.51 g.cm(-3), with electrical conductivities up to 24 kS.m(-1) and tensile strengths over 10 MPa, these tapes exhibit the best combination of properties with respect to density heretofore observed for carbon-based papers, membranes, or films.

We present a general method for characterizing the intrinsic electrochemical properties of graphene sheets, such as the specific double-layer capacitance, in the absence of porosity-related artifacts and uncertainties. By assembling densely tiled monolayers of electrically insulating or conductive functionalized graphene sheets onto electrode substrates (gold and highly oriented pyrolytic graphite), we demonstrate our ability to isolate their intrinsic electrochemical response in terms of surface-specific double-layer capacitance and redox behavior. Using this system, the electrochemical properties of various types of graphene can be directly compared without the need to take into account changes in electrode morphology and electrolyte accessibility arising because of varying material properties.

We studied the local voltage drop in functionalized graphene sheets of sub mu m size under external bias conditions by Kelvin probe force microscopy. Using this noninvasive experimental approach, we measured ohmic current-voltage characteristics and an intrinsic conductivity of about 3.7 x 10(5) S/m corresponding to a sheet resistance of 2.7 k Omega/sq under ambient conditions for graphene produced via thermal reduction of graphite oxide. The contact resistivity between functionalized graphene and metal electrode was found. to be <6.3 x 10(-7) Omega cm(2).

Kelvin probe force microscopy was used to study the impact of contacts and topography on the local potential distribution on contacted, individual functionalized graphene sheets (FGS) deposited on a SiO2/Si substrate. Negligible contact resistance is found at the graphene/Ti interface and a graphene resistance of 2.3 k Omega is extracted for a single sheet with sub-mu m size. Pronounced steps in the topography, which we attribute to a variation of the spacing between graphene and substrate, result in a significant change of the local resistivity.

A functionalized graphene sheet-sulfur (FGSS) nanocomposite was synthesized as the cathode material for lithium-sulfur batteries. The structure has a layer of functionalized graphene sheets/stacks (FGS) and a layer of sulfur nanoparticles creating a three-dimensional sandwich-type architecture. This unique FGSS nanoscale layered composite has a high loading (70 wt%) of active material (S), a high tap density of similar to 0.92 g cm(-3), and a reversible capacity of similar to 505 mAh g(-1) (similar to 464 mAh cm(-3)) at a current density of 1680 mA g(-1) (1C). When coated with a thin layer of cation exchange Nafion film, the migration of dissolved polysulfide anions from the FGSS nanocomposite was effectively reduced, leading to a good cycling stability of 75% capacity retention over 100 cycles. This sandwich-structured composite conceptually provides a new strategy for designing electrodes in energy storage applications.

Carbon-supported precious metal catalysts are widely used in heterogeneous catalysis and electrocatalysis, and enhancement of catalyst dispersion and stability by controlling the interfacial structure is highly desired. Here we report a new method to deposit metal oxides and metal nanoparticles on graphene and form stable metal-metal oxide-graphene triple junctions for electrocatalysis applications. We first synthesize indium tin oxide (ITO) nanocrystals directly on functionalized graphene sheets, forming an ITO-graphene hybrid. Platinum nanoparticles are then deposited, forming a unique triple-junction structure (Pt-ITO-graphene). Our experimental work and periodic density functional theory (DFT) calculations show that the supported Pt nanoparticles are more stable at the Pt-ITO-graphene triple junctions. Furthermore, DFT calculations suggest that the defects and functional groups on graphene also play an important role in stabilizing the catalysts. These new catalyst materials were tested for oxygen reduction for potential applications in polymer electrolyte membrane fuel cells, and they exhibited greatly enhanced stability and activity.

We present a molecular dynamics (MD) simulation study of the structure and energetics of thin films of water adsorbed on solid substrates at 240 K. By considering crystalline silica as a model hydrophilic surface, we systematically investigate the effect of film thickness on the hydrogen bonding, density, molecular orientation, and energy of adsorbed water films over a broad surface coverage range (delta). At the lowest coverage investigated (delta = 1 monolayer, >90% of water molecules form three hydrogen bonds (H-bonds) with surface silanol groups and none with other water molecules; when delta = 1 ML, the most probable molecular orientation is characterized by both the molecular dipole and the OH vectors being parallel to the surface. As 6 increases, water-water and water-surface interactions compete, leading to the appearance of an orientational structure near the solid-liquid interface characterized by the dipole moment pointing toward the silica surface. We find that the water-surface H-bond connectivity and energetics of the molecular layer nearest to the solid liquid interface do not change as delta increases. Interfacial water molecules, therefore, are able to reorient and form water-water H-bonds without compromising water-surface interactions. The surface-induced modifications to the orientational structure of the adsorbed film propagate up to similar to 1.4 nm from the solid-liquid interface when delta = 15.1 ML (a film that is similar to 2.3 run thick). For the thinner adsorbed films (delta <= 4.3 ML, thickness <= 0.8 nm) orientational correlations imposed by the solid liquid and liquid-vapor interfaces are observed throughout.

Functionalized graphene sheets having a C to O molar ratio of at least ∼23:1 and method of prepg. the same. [on SciFinder(R)]

In a nanocomposite compn. having a silicone elastomer matrix having therein a filler loading of greater than 0.05 wt %, based on total nanocomposite wt., the filler is functional graphene sheets (FGS) having a surface area of from 300 m2/g to 2630 m2/g; and a method for producing the nanocomposite and uses thereof. [on SciFinder(R)]

Nanocomposite materials consist of a metal oxide bonded to at least one graphene material. The graphene layer has a carbon to oxygen ratio of (20-500):1 and a surface area of 600-2630 m2/g. The metal oxide can be an oxide of Ti, Sn, Ni, Mn, V, Si, or Co, preferably titania in the form of rutile or anatase, or tin oxide. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate of ⪆10 C. The nanocomposite material is prepd. by providing graphene in a first suspension; dispersing the graphene with a surfactant, esp. sodium dodecyl sulfate; adding a metal oxide precursor to the dispersed graphene to form a second suspension; and pptg. the metal oxide from the second suspension onto at least one surface of the dispersed graphene to form the nanocomposite material. The nanocomposite material can be used in an energy storage device, esp. in a lithium ion battery as electrode material. [on SciFinder(R)]

Nanocomposite materials consists of a metal oxide bonded to at least one graphene material. The graphene layer has a carbon to oxygen ratio of (20-500):1 and a surface area of 600-2630 m2/g. The metal oxide can be an oxide of Ti, Sn, Ni, Mn, V, Si, or Co, preferably titania in the form of rutile or anatase, or tin oxide. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate of ⪆10 C. The nanocomposite material is prepd. by providing graphene in a first suspension; dispersing the graphene with a surfactant, esp. sodium dodecyl sulfate; adding a metal oxide precursor to the dispersed graphene to form a second suspension; and pptg. the metal oxide from the second suspension onto at least one surface of the dispersed graphene to form the nanocomposite material. The nanocomposite material can be used in an energy storage device, esp. in a lithium ion battery as electrode material. [on SciFinder(R)]

Fibers comprise a compn. including a polymer and graphene sheets. The fibers can be further formed into yarns, cords, and fabrics. The fibers can be polyamide, polyester, acrylic, acetate, modacrylic, spandex, lyocell fibers, and the like. Such fibers can take on a variety of forms, including, staple fibers, spun fibers, monofilaments, multifilaments, and the like. [on SciFinder(R)]

The reinforcing component of these articles includes a compn. made from at least one polymer and graphene sheets. [on SciFinder(R)]

A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from ∼300-2600 m2/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as detd. by x-ray diffraction. [on SciFinder(R)]

Tire cords comprising fibers including at least one polymer and graphene sheets. Graphene sheets are added to poly(ethylene terephthalate) (PET) by melt compounding in an extruder to yield a PET compn. comprising about 0.25 wt.% graphene sheets. The PET compn. is then solid phase polymd. at 215° to an IV of about 1 dL/g. The compn. is spun into monofilaments that are then post drawn to a draw ratio of about 4 to 5. After drawing, the filaments have a diam. of about 120 μ. The storage modulus of the monofilaments is then measured as a function of temp. using a dynamic mech. analyzer (DMA). [on SciFinder(R)]

Graphene-based electrodes have recently gained popularity due to their superior electrochemical properties. However, the exact mechanisms of electrochemical activity are not yet understood. Here, we present data from NADH oxidation and ferri/ferrocyanide redox probe experiments to demonstrate that both (i) the porosity of the graphene electrodes, as effected by the packing morphology, and (ii) the functional group and the lattice defect concentration play a significant role on their electrochemical performance.

When applied on the counter electrode of a dye-sensitized solar cell, functionalized graphene sheets with oxygen-containing sites perform comparably to platinum (conversion efficiencies of 5.0 and 5.5%, respectively, at 100 mW cm(-2) AM1.56 simulated light). To interpret the catalytic activity of functionalized graphene sheets toward the reduction of triiodide, we propose a new electrochemical impedance spectroscopy equivalent circuit that matches the observed spectra features to the appropriate phenomena. Using cyclic voltammetry, we also show that tuning our material by increasing the amount of oxygen-containing functional groups can improve its apparent catalytic activity. Furthermore, we demonstrate that a functionalized graphene sheet based ink can serve as a catalytic, flexible, electrically conductive counter electrode material.

Graphene, emerging as a true 2-dimensional material, has received increasing attention due to its unique physicochemical properties (high surface area, excellent conductivity, high mechanical strength, and ease of functionalization and mass production). This article selectively reviews recent advances in graphene-based electrochemical sensors and biosensors. In particular, graphene for direct electrochemistry of enzyme, its electrocatalytic activity toward small biomolecules (hydrogen peroxide, NADH, dopamine, etc.), and graphene-based enzyme biosensors have been summarized in more detail; Graphene-based DNA sensing and environmental analysis have been discussed. Future perspectives in this rapidly developing field are also discussed.

An electrochemical sensor based on the electrocatalytic activity of functionalized graphene for sensitive detection of paracetamol is presented. The electrochemical behaviors of paracetamol on graphene-modified glassy carbon electrodes (GCEs) were investigated by cyclic voltammetry and square-wave voltammetry. The results showed that the graphene-modified electrode exhibited excellent electrocatalytic activity to paracetamol. A quasi-reversible redox process of paracetamol at the modified electrode was obtained, and the over-potential of paracetamol decreased significantly compared with that at the bare GCE. Such electrocatalytic behavior of graphene is attributed to its unique physical and chemical properties, e.g., subtle electronic characteristics, attractive pi-pi interaction, and strong adsorptive capability. This electrochemical sensor shows an excellent performance for detecting paracetamol with a detection limit of 3.2 x 10(-8) M, a reproducibility of 5.2% relative standard deviation, and a satisfied recovery from 96.4% to 103.3%. The sensor shows great promise for simple, sensitive, and quantitative detection and screening of paracetamol. (C) 2010 Elsevier B.V. All rights reserved.

Nitrogen-doped graphene (N-graphene) is obtained by exposing graphene to nitrogen plasma. N-graphene exhibits much higher electrocatalytic activity toward oxygen reduction and H(2)O(2) reduction than graphene, and much higher durability and selectivity than the widely-used expensive Pt for oxygen reduction. The excellent electrochemical performance of N-graphene is attributed to nitrogen functional groups and the specific properties of graphene. This indicates that N-graphene is promising for applications in electrochemical energy devices (fuel cells, metal-air batteries) and biosensors.

A novel electrochemical immunosensor for sensitive detection of cancer biomarker alpha-fetoprotein (AFP) is described that uses a graphene sheet sensor platform and functionalized carbon nanospheres (CNSs) labeled with horseradish peroxidase-secondary antibodies (HRP-Ab2). Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy: first, the synthesized CNSs yielded a homogeneous and narrow size distribution, which allowed several binding events of HRP-Ab2 on each nanosphere. Enhanced sensitivity was achieved by introducing the multibioconjugates of HRP-Ab2-CNSs onto the electrode surface through "sandwich" immunoreactions. Second, functionalized graphene sheets used for the biosensor platform increased the surface area to capture a large amount of primary antibodies (Ab1), thus amplifying the detection response. On the basis of the dual signal amplification strategy of graphene sheets and the multienzyme labeling, the developed immunosensor showed a 7-fold increase in detection signal compared to the immunosensor without graphene modification and CNSs labeling. The proposed method could respond to 0.02 ng mL(-1) AFP with a linear calibration range from 0.05 to 6 ng mL(-1). This amplification strategy is a promising platform for clinical screening of cancer biomarkers and point-of-care diagnostics.

Surfactant or polymer directed self-assembly has been widely investigated to prepare nanostructured metal oxides, semiconductors, and polymers, but this approach is mostly limited to two-phase materials, organic/inorganic hybrids, and nanoparticle or polymer-based nanocomposites. Self-assembled nanostructures from more complex, multiscale, and multiphase building blocks have been investigated with limited success. Here, we demonstrate a ternary self-assembly approach using graphene as fundamental building blocks to construct ordered metal oxide-graphene nanocomposites. A new class of layered nanocomposites is formed containing stable, ordered alternating layers of nanocrystalline metal oxides with graphene or graphene stacks. Alternatively, the graphene or graphene stacks can be incorporated into liquid-crystal-templated nanoporous structures to form high surface area, conductive networks. The self-assembly method can also be used to fabricate free-standing, flexible metal oxide-graphene nanocomposite films and electrodes. We have investigated the Li-ion insertion properties of the self-assembled electrodes for energy storage and show that the SnO2-graphene nanocomposite films can achieve near theoretical specific energy density without significant charge/discharge degradation.

A gas diffusion barrier contains a polymer matrix and a functional graphene which displays no signature of graphite and/or graphite oxide, as detd. by X-ray diffraction. [on SciFinder(R)]