Chemically-reduced Graphene Research Articles

The electrochemical activities of anthraquinone monosulfonate adsorbed on the basal plane of reduced graphene oxide by π–π stacking interaction

The electrochemical properties of anthraquinone monosulfonate (AQS) adsorbed on the basal plane of chemically-reduced graphene oxide (RGO) by π–π stacking interaction were investigated. The AQS/RGO nanocomposites were synthesized via a simple reduction–adsorption method and characterized with various techniques, and the surface concentration of AQS on the basal plane of RGO was estimated to be 1.72 × 10−12 mol cm−2. Electrochemical tests showed that the AQS/RGO nanocomposites accelerated the heterogeneous electron transfer, when ferro/ferricyanide was used as a redox probe, and RGO facilitated the electron transfer between AQS and the surface of glassy carbon electrode, producing a well-defined redox couple centered at −0.490 V versus SCE at neutral medium. Compared with AQS and RGO modified glassy carbon (GC) electrode, the AQS/RGO nanocomposites showed better electrocatalytic activity towards oxygen reduction reaction. Rotating disk electrode data showed that the reduction of O2 on AQS/RGO/GC electrode underwent a two-electron process to H2O2 at low overpotential and shifted to four-electron reduction to H2O at relatively high overpotential. The present work demonstrates that AQS can be an efficient catalyst when noncovalently functionalized on the basal plane of RGO for electrochemical applications.

Morphology controlled high performance supercapacitor behaviour of the Ni–Co binary hydroxide system

The morphology evolution of the Ni–Co binary hydroxides was studied varying from nanosheets, to nanoplate–nanospheres, to nanorods and to a nanoparticle geometry by simply controlling the Co:Ni ratio in the initial reactant. High capacitances of 1030 F g−1 and 804 F g−1 can be achieved in the 1-D nanorod morphology at mass loading of 1 mg cm−2 and 2.8 mg cm−2 at a current density of 3 A g−1, respectively. To demonstrate its practical application, the binary hydroxide electrode was coupled with chemically-reduced graphene (CG) forming an asymmetric supercapacitor in order to improve the potential window and thus energy density. The asymmetric supercapacitor delivers a high energy density of 26.3 Wh kg−1 at the power density of 320 W kg−1. The approach of controlling morphology and crystallinity of the binary system for optimizing supercapacitive performance may be applied developing other promising multiply metal hydroxide/oxide systems for supercapacitor applications.

Self-assembled oligo(phenylene ethynylene)s/graphene nanocomposite with improved electrochemical performances for dopamine determination

In this work, a novel 1,4-bis (4- aminophenylethynyl)benzene (OPE-NH2, a symmetric linear conjugated oligo(phenylene ethynylene)s derive) and chemically-reduced graphene oxide (rGO) nanocomposite (OPE-NH2/rGO) was synthesized by a simple self-assembly method. The OPE-NH2/rGO nanocomposite was stable and water soluble. The formation of OPE-NH2/rGO nanocomposite was ascribed to the π–π stacking interaction between the conjugated structure of OPE-NH2 and rGO as well as the electrostatic force between the amino group of OPE-NH2 and the carboxyl group on rGO, which was characterized by FT-IR, UV–vis spectra and fluorescence spectra. The OPE-NH2/rGO nanocomposite exhibited significantly improved electrocatalytic activity to the oxidization of dopamine (DA) than that of rGO or OPE-NH2. The electrochemical performances of OPE-NH2/rGO were dependent on the OPE-NH2 contents, and OPE-NH2 content of 5wt% exhibited the highest activity. Compared with that of rGO, the nanocomposite presented superior high sensitivity with detection limit of 5nM, excellent selectivity, wide linear range (0.01–60μM) and good stability on the determination of DA. The practical application of the developed OPE-NH2/rGO nanocomposite modified electrode was successfully demonstrated for DA determination in human serum samples.

Preparation and properties of graphene oxide–carbon fiber/phenolic resin composites

Graphene oxide–carbon fiber/phenolic resin, chemically-reduced graphene oxide–carbon fiber/phenolic resin, and thermally-reduced graphene oxide–carbon fiber/phenolic resin composites were prepared by blending a graphene oxide suspension in an ethanol solution of phenolic resin with carbon fibers, followed by vacuum drying and hot pressing. The effects of the type of graphene oxide on structure, compressive performance and friction properties of the composites were investigated. Results showed that the compressive properties of the composites were greatly improved with a 0.1 mass graphene oxide % loading compared with the pure carbon fiber/phenolic resin composite. The compressive strength and modulus of the thermally-reduced graphene oxide/phenolic resin/carbon fiber composites were increased by 178.9%, 129.5%, respectively, and the highest energy storage modulus of the chemically-reduced graphene oxide/phenolic resin/carbon fiber composite was increased by 75.2% compared with the pure carbon fiber/phenolic resin composite. The glass transition temperatures of all the composites containing graphene oxide decreased. [ New Carbon Materials 2012;27(5):377–84 ]

Novel conductive epoxy composites composed of 2-D chemically reduced graphene and 1-D silver nanowire hybrid fillers

In this study, 1-D Ag nanowires (NWs), 2-D chemically reduced graphene (CRG), and hybrid CRG–Ag NW fillers were investigated for use as conductive epoxy composites. By combining the 2-D CRG with 1-D Ag NWs, the percolation limit of the Ag NWs decreased from 30 wt% to 10 wt% and the electrical conductivity was dramatically enhanced because of the decreased tunneling resistance between the Ag NWs due to the thin 2-D conductive CRGs. Their thermal and mechanical properties were also improved due to the chemical crosslinking effects between CRGs and the hardener in the epoxy matrix as well as the physical crosslinking effects between nano-structures and polymer chains. The break strength of the CRG/Ag-NW/epoxy composite was 50% higher than that of the pure epoxy resin.

Composites of chemically-reduced graphene oxide sheets and carbon nanospheres with three-dimensional network structure as anode materials for lithium ion batteries

It is challenging to develop lithium ion batteries (LIBs) possessing simultaneously large reversible capacity, high rate capability, and good cycling stability, which are in turn determined mainly by the component materials of batteries. We designed and synthesized a series of composites of chemically-reduced graphene oxide (CRG) sheets and carbon nanospheres (CNS). It was illustrated that within the as-obtained composites the CNSs were fully cladded and bridged with CRG sheets forming a three-dimensional (3D) network with cavities and pores. Coin cells using the anodes made of the as-obtained composites with appropriate composition exhibit large reversible capacity, high rate capability, and good cycling stability. The highest reversible specific capacity could reach up to 925 mA h g−1 and 604 mA h g−1 at charge–discharge current densities of 5 A g−1 and 10 A g−1, respectively, and faint capacity and rate capability fades were detected even after 200 charge–discharge cycles. The excellent electrochemical performance of the anodes made of the as-obtained composites in the LIBs originates from the unique 3D network structure and the intrinsic properties of CRG and CNS that provide plenty of transportation pathways for electron and Li+, and sufficient tolerant sites for Li/Li+.

Green Approach To Prepare Graphene-Based Composites with High Microwave Absorption Capacity

Chemically reduced graphene (CR-G)/poly(ethylene oxide) (PEO) composites are prepared by a simple aqueous mixing method. Graphite oxide (GO) is prepared by a modified Hummers method and further dispersed in water to form graphene oxide (G-O). The as prepared G-O is mixed with PEO and in situ reduced by l-ascorbic acid. CR-G monolayers are ∼1 nm in thickness and ∼1.5 μm in both length and width as confirmed by AFM, indicating their large aspect ratio of about 1500. G-O is dispersed in PEO at the molecular level due to hydrogen bonding, and PEO acts as a barrier for CR-G layers to prevent agglomeration during the process of reduction. CR-G/PEO composites have high permittivity, resulting from the uniform dispersion of electrically conductive CR-G with high aspect ratio. CR-G/PEO composite (2.6 vol %) shows high microwave absorbing capacity as its minimum reflection loss is −38.8 dB. CR-G sheets form a huge number of electrical pathways which can dissipate microwave energy into heat effectively as well as dielectric relaxation and interface scattering induced by large CR-G/PEO interfaces.

Sensitive detection of rutin based on β-cyclodextrin@chemically reduced graphene/Nafion composite film

An electrochemical sensor based on chemically reduced graphene (CRG) was developed for the sensitive detection of rutin. To construct the base of the sensor, a novel composite was initially fabricated and used as the substrate material by combining CRG and β-cyclodextrin (β-CD) via a simple sonication-induced assembly. Due to the high rutin-loading capacity on the electrode surface and the upstanding electric conductivity of graphene, the electrochemical response of the fabricated sensor was greatly enhanced and displayed excellent analytical performance for rutin detection from 6.0×10−9 to 1.0×10−5molL−1 with a low detection limit of 2.0×10−9molL−1 at 3σ. Moreover, the proposed electrochemical sensor also exhibited good selectivity and acceptable reproducibility and could be used for the detection of rutin in real samples. Therefore, the present work offers a new way to broaden the analytical applications of graphene in pharmaceutical analysis.

Thermomechanical properties of chemically modified graphene/poly(methyl methacrylate) composites made by in situ polymerization

The morphology and thermomechanical properties of composites of poly(methyl methacrylate) (PMMA) and chemically modified graphene (CMG) fillers were investigated. For composites made by in situ polymerization, large shifts in the glass transition temperature were observed with loadings as low as 0.05 wt.% for both chemically-reduced graphene oxide (RG-O) and graphene oxide (G-O)-filled composites. The elastic modulus of the composites improved by as much as 28% at just 1 wt.% loading. Mori–Tanaka theory was used to quantify dispersion, suggesting platelet aspect ratios greater than 100 at low loadings and a lower quality of dispersion at higher loadings. Fracture strength increased for G-O/PMMA composites but decreased for RG-O/PMMA composites. Wide angle X-ray scattering suggested an exfoliated morphology of both types of CMG fillers dispersed in the PMMA matrix, while transmission electron microscopy revealed that the platelets adopt a wrinkled morphology when dispersed in the matrix. Both techniques suggested similar exfoliation and dispersion of both types of CMG filler. Structural characterization of the resulting composites using gel permeation chromatography and solid state nuclear magnetic resonance showed no change in the polymer structure with increased loading of CMG filler.

Supercapacitor based on graphene and ionic liquid electrolyte

A new kind of supercapacitor by using chemical reduced graphene (CRG) as electrode material and ionic liquid with addition of acetonitrile as electrolyte is assembled and investigated. CRG materials with high surface area are prepared by chemical reduction of graphene oxide. The capacitive properties of the supercapacitor composed of the CRG and ionic liquid electrolyte are studied by electrical impedance spectroscopy, cyclic voltammetry and galvanostatic charge–discharge. With the combined advantages of graphene and ionic liquid, the supercapacitor shows perfect performance. The supercapacitor possesses wide cell voltage and good stability. The specific capacitance, energy density, and specific power density of the present supercapacitor are 132 Fg−1, 143.7 Wh kg−1, and 2.8 kW kg−1, respectively. The results demonstrate the potential application of electrical energy storage devices with high performance based on this new kind of supercapacitor.

Thin films of carbon nanotubes and chemically reduced graphenes for electrochemical micro-capacitors

We report the making of chemically reduced graphene (CRG) sheets separated by layer-by-layer-assembled multi-walled carbon nanotubes (MWCNTs) for electrochemical micro-capacitor applications. Submicron thin films of amine-functionalized MWCNTs (MWCNT-NH 2) and CRG derived from graphene oxides, were shown to be cross-linked with amide bonds having high packing densities of ∼70%. These carbon-only electrodes were found to have large volumetric capacitance of ∼ 160 F/cm electrode 3 in an acidic electrolyte (0.5 M H 2SO 4). The electrode capacitance in a neutral electrolyte (1 M KCl) was found much lower, which supported the hypothesis that the observed high capacitances in the acidic electrolyte can be attributed primarily to redox reactions between protons and surface oxygen-containing groups on carbon.

Comparative study of different types of graphenes as electrocatalysts for ascorbic acid

A comparative study regarding the electrocatalytic activity of graphene oxide (GO), chemically-reduced graphene oxide ( crGO) and graphene produced by direct liquid exfoliation ( dG) is presented. Sensors were developed by modifying glassy carbon (GC) electrodes with GO, crGO and dG and ascorbic acid was used as a pilot analyte. GC/GO electrodes offer substantially lower oxidation overpotential, up to 350 mV, compared with GC/ crGO, GC/ dG and unmodified GC electrodes. In addition, the different carbon-to-oxygen atomic ratios in GO, as it occurs depending on the synthetic route, were found to have a remarkable effect on the performance of the sensors. Reduction of GO was achieved by immersing the modified electrodes into a stirred solution of NaBH 4 for 10 min at room temperature. This process was used alternatively of the time consuming and laborious process of hydrazine, and its effectiveness was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Analytical utility of the sensors is demonstrated.

High yield fabrication of chemically reduced graphene oxide field effect transistors bydielectrophoresis

We demonstrate high yield fabrication of field effect transistors (FET) using chemicallyreduced graphene oxide (RGO) sheets. The RGO sheets suspended in water were assembledbetween prefabricated gold source and drain electrodes using ac dielectrophoresis. With theapplication of a backgate voltage, 60% of the devices showed p-type FET behavior, whilethe remaining 40% showed ambipolar behavior. After mild thermal annealing at200 °C, all ambipolar RGO FET remained ambipolar with increased hole andelectron mobility, while 60% of the p-type RGO devices were transformed toambipolar. The maximum hole and electron mobilities of the devices were 4.0 and1.5 cm2 V − 1 s − 1 respectively. High yield assembly of chemically derived RGO FET will have significantimpact in scaled up fabrication of graphene based nanoelectronic devices.

Fabrication of highly conducting and transparent graphene films

Graphene-based transparent conducting films were prepared using the following method. A chemically-reduced graphene dispersion was synthesized and graphene films were prepared from it by transfer printing, followed by thermal treatment. The resulting graphene films possessed an excellent electrical conductivity with a high transparency. A sheet resistance lower than ∼2 KΩ/sq and a transparency well over 80% were achieved at a typical wavelength of 550 nm. These properties are considered quite sufficient for many applications, such as transparent conductor films for touch panels.

Processing of Graphene for Electrochemical Application: Noncovalently Functionalize Graphene Sheets with Water-Soluble Electroactive Methylene Green

To explore graphene applications in various fields, the processability of graphene becomes one of the important key issues, particularly with the increasing availability of synthetic graphene approaches, because the direct dispersion of hydrophobic graphene in water is prone to forming agglomerates irreversibly. Here, a facile method is proposed to increase the dispersity of graphene through noncovalent functionalization graphene with a water-soluble aromatic electroactive dye, methylene green (MG), during chemical reduction of graphene oxide (GO) with hydrazine. Atomic force microscopic and UV-vis spectrophotometric results demonstrate that chemically reduced graphene (CRG) functionalized with MG (CRG-MG) is well-dispersed into water through the coulomb repulsion between MG-adsorbed CRG sheets. The electrochemical properties of the formed CRG-MG are investigated, and the results demonstrate that CRG-MG confined onto a glassy carbon (GC) electrode has lower charge-transfer resistance and better electrocatalytic activity toward the oxidation of NADH, in relation to pristine CRG (i.e., without MG functionalization). This method not only offers a facile approach to dispersing graphene in water but also is envisaged to be useful for investigations on graphene-based electrochemistry.