Reduced Graphene Sheets Research Articles

Large scale production of nanoporous graphene sheets and their application in lithium ion battery

Nanoporous graphene sheets were generated through a simple thermal annealing procedure using composites of ferrocene nanoparticles and graphene oxide sheets as precursors in a large scale. The morphology, composition, and formation mechanism of the as-obtained nanoporous graphene sheets were studied complementarily with scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and other spectroscopy techniques. We found that the density of nanopores on the graphene sheet was determined by the surface distribution of oxygen-containing groups on the original graphene oxide sheets. The coin cells using nanoporous graphene sheets as anode materials showed higher specific lithium ion storage capacity, better discharge/charge rate capability and higher cycling stability when compared to the coin cells with graphene or chemically reduced graphene sheets as anodes.

Rapid one-step synthesis and electrochemical properties of graphene/carbon nanotubes/MnO2 composites

A composite consisting of reduced graphene sheets, multi-walled carbon nanotubes, and MnO2 (RGO/CNT/MnO2) was prepared using a facile and efficient one-step method under microwave irradiation. Graphene oxide could be easily reduced without any additional reducing reagents. Potassium permanganate was used as starting materials for the growth of MnO2 on the graphene sheets and carbon nanotubes. Owing to the synergic effect of the ternary component, the electrode exhibited a high rate capacitance, such as 915Fg−1 of specific capacitance at 0.2Ag−1, as well as excellent cycling stability (98.1% capacitance retention after 1500 cycles). On the other hand, the results suggest that our research opens up the possibility for the fabrication of high-performance energy-storage devices of multi-component electrodes.

Highly Efficient Synthesis of Neat Graphene Nanoscrolls from Graphene Oxide by Well-Controlled Lyophilization

Graphene nanoscroll (GNS) is an important one-dimensional tubular form of graphitic carbon with characteristic open topology. It has been predicted to possess extraordinary properties that are significantly different from the analogical multiwalled carbon nanotubes. However, comprehensive experimental investigations on its properties and applications are still hindered by the lack of its reliable synthesis in high yield. To efficiently transform the scalable graphene oxide sheets into GNSs, here, we proposed a well-controlled lyophilization that comprises four sequential steps: chemical reduction of giant GO, freezing isolation of reduced graphene sheets, freeze-drying, and thermal annealing. The combined method has an extremely high efficiency, up to the record 92%. Systemic control experiments and cryo-SEM inspections revealed that the topological transformation from 2D sheet to 1D scroll is the sublimation-induced scrolling of individually confined graphene sheets in ice, which was controlled by chemic...

Fabrication of water-dispersible and highly conductive PSS-doped PANI/graphene nanocomposites using a high-molecular weight PSS dopant and their application in H2S detection.

This work describes the fabrication of poly(4-styrenesulfonic acid)-doped polyaniline/graphene (PSS-doped PANI/graphene) nanocomposites and their use as sensing elements for hydrogen sulfide (H2S) detection. PSS with a weight-average molecular weight (Mw) of 1.96 × 10(6) was synthesized using low-temperature free-radical polymerization. The PSS was used as both a doping agent and a binding agent for the polymerization of aniline monomers in a biphasic system (water-chloroform) at -50 °C. The high Mw of PSS resulted in relatively large particle sizes and smooth surfaces of the PSS-doped PANI. These physical characteristics, in turn, resulted in low interparticle resistance and high conductivity. In addition, the PSS allowed homogeneous dispersion of reduced graphene sheets through electrostatic repulsion. The prepared PSS-doped PANI/graphene solutions showed good compatibility with flexible poly(ethylene terephthalate) (PET) substrates, making them suitable for flexible sensor electrodes. Changes in the charge-transport properties, such as protonation level, conjugation length, crystalline structure, and charge-transfer resistance, of the electrode materials were the main factors influencing the electrical and sensor performance of the PSS-doped PANI-based electrodes. PSS-doped PANI/graphene composites containing 30 wt% graphene showed the highest conductivity (168.4 S cm(-1)) and the lowest minimum detection level (MDL) for H2S gas (1 ppm). This result is consistent with the observed improvements in charge transport in the electrode materials via strong π-π stacking interactions between the PANI and the graphene sheets.

Synthesis of boron and nitrogen doped graphene supporting PtRu nanoparticles as catalysts for methanol electrooxidation

In this study, we demonstrate a single-step heat treatment approach to synthesize boron and nitrogen doped graphene supporting PtRu electrocatalysts for methanol electro-oxidation reaction. The reduction of graphene oxide, boron or nitrogen doping of graphene and loading of PtRu nanoparticles happened simultaneously during the reaction process. The morphologies and microstructures of the as-prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic methanol oxidation activity and durability of the obtained catalysts were evaluated by the cyclic voltammetry and chronoamperometric techniques. The results reveal that the boron and nitrogen doped graphene supporting PtRu electrocatalysts can be successfully prepared by the single step heat treatment technique, and the introduction of boron or nitrogen containing function groups into the reduced graphene sheets could modulate the particle size and dispersion of the supporting PtRu nanoparticles and improve the electrocatalytic performance of methanol oxidation reaction. The optimal annealing temperature is 800°C, the preferable heat treatment time is 60min for the nitrogen-doped catalysts and 90min for the boron-doped catalysts, and the catalysts prepared under such conditions present superior catalytic activities for methanol oxidation than those prepared under other heat treatment conditions.

Synthesis of silanized maghemite nanoparticles onto reduced graphene sheets composites

Novel γ-Fe2O3@APTES@rGO composites are successfully synthesized by using graphene oxide and silanized maghemite nanoparticles. Graphene oxide and maghemite were obtained by Hummers and Massart methods, respectively. The silanization process was done to functionalize maghemite surface with a controllable quantity of amino groups. Then, by adding aqueous graphene oxide suspension, the bonding between graphene oxide and silanized maghemite nanoparticles was done in refluxing conditions. Afterwards, chemical reduced graphene oxide reaction was realized by addition of hydrazine solution. The characterization of γ-Fe2O3@APTES@rGO composites was studied by X-ray Diffraction, Fourier Transformed Infrared Spectroscopy, thermogravimetric analysis and scanning electron microscopy.

Facile structural tuning and compositing of iron oxide-graphene anode towards enhanced supacapacitive performance

Hydrothermal has been demonstrated to effectively tune the various morphologies of nanostructured Fe2O3 materials from 0D nanoparticles, 1D nanorods to self-assembled nanorods which form 3D ovoid architecture. Subsequently, compositing and reduction of graphene oxide (GO) were carried out simultaneously via facile base reduction. The as-synthesized nanocomposite was fabricated into an electrode material of hybrid supercapacitor and characterized by cyclic voltammetry (CV), and galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS). The synergistic effects of highly uniform 1D Fe2O3 nanorods of low internal resistance, enhanced ion diffusion as well reduced graphene sheets incorporation lead to superior electrochemical performances. The nanocomposite exhibits pseudocapacitive properties of high specific capacitance ~504Fg−1 at 2mA/cm2. Although many metal oxide and reduced GO hybrid systems have been investigated as electrode materials, this study demonstrates simple and effective tuning of Fe2O3 nanostructures morphologies to significantly impact the pseudocapacitive performances.

Facile Growth of Cu2O Nanowires on Reduced Graphene Sheets with High Nonenzymatic Electrocatalytic Activity Toward Glucose

In this work, we demonstrate the fabrication of a unique hybrid structure by directly growing ultrathin Cu2O nanowires (about 5 nm in diameter) onto reduced graphene oxide (rGO) sheets via a facile solvothermal method. This is a facile process carried out at 120°C for 6 h, in which only cupric acetate and rGO sheets are used as initiating materials, ethylene glycol as the solvent and reducing agent, and soldium acetate as precipitator, without employing any additional surfactant. Furthermore, the as‐obtained nanocomposites‐modified glassy carbon electrode (GCE) shows significantly improved electrochemical performance in nonenzymatic amperometric glucose detection, exhibiting the good linear behavior with glucose concentrations ranging from 10 μM to 0.1 mM with a high gradient of 80.17 μA/mM. More importantly, interference from the oxidation of common interfering species under physiological conditions, such as uric acid, dopamine, and ascorbic acid, is effectively avoided. Therefore, these nanocomposites may be a promising electrode material for the determination of glucose.

Synthesis of graphene-based Co-B catalyst via simultaneous chemical reduction for hydrolysis of sodium borohydride

Co-B nanoparticles are deposited on graphene sheets by simultaneous chemical reduction of Co+2 and graphite oxides using NaBH4 as the reducing agent. The reduced Co−B/graphene nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results show that after reduction, not only considerable amount of functional groups has been removed but also exhibited formation of Co-B alloy on the graphene sheets. The catalytic activity of nanocomposites was investigated by the hydrolysis of NaBH4 in aqueous solution. Graphene support material greatly enhances the hydrolysis of NaBH4 with respect to graphite and active carbon supports, and chemical reduced graphene sheets can readily form stable aqueous colloids through electrostatic stabilization. The present method is promising for the synthesis of effective supported catalysts for hydrolysis of NaBH4.

Reduced Graphene Oxide/InGaZn Mixed Oxide Nanocomposite Photocatalysts for Hydrogen Production

A series of reduced graphene oxide and indium-gallium-zinc mixed oxide (RGO/IGZ) nanocomposites were successfully synthesised by a simple one-step hydrothermal method. The as-synthesised nanocomposites were characterised by crystallographic, microscopic, and spectroscopic methods to explore the robust photocatalytic activity of the prepared materials. XRD patterns confirmed the formation of highly pure, single-phase, hexagonal In2 Ga2 ZnO7 with no impurity-related peaks. All the photocatalysts absorbed visible light as observed from the diffuse reflectance UV/Vis spectra. The electron-hole recombination is effectively minimised by the formation of an RGO/metal oxide nanocomposite, which was successfully derived from a photoluminescence (PL) study and photoelectrochemical measurements. The decoration of IGZ nanocrystals onto reduced graphene sheets leads to significant quenching of its luminescent intensity, dramatically improved photocurrent generation (33 times more than neat IGZ) and significantly enhanced photostability. The high photocatalytic activity for H2 production is explained by the strong interaction between the IGZ nanocrystals with RGO sheets, low PL intensity, high photocurrent and large surface area.

Super-Hydrophobic Film Prepared with Reduced Graphene Sheets and its Application as Corrosion Barrier to Copper

Electrophoretic deposition is proposed to fabricate super-hydrophobic film on copper surface with reduced graphene sheets (RGSs). The resulted film was characterized with contact angle meter, scanning electron microscopy and so on. It is found that the film presents super-hydrophobic property with water contact angle of 150.4°. Air can be trapped in the island-like structure and intensify the wettability of film. Electrochemical measurements prove that super-hydrophobic film can inhibit corrosion process of underlying copper by inducing both anodic and cathodic current density. This method for super-hydrophobic film fabrication is facial and time-saving, and it will expand the application of RGSs in mechanical engineering.

Thermal Reduction of Graphene Oxide in Organic Solvents for Producing Colloidal Suspensions of Reduced Graphene Oxide Sheets

A new method for preparing graphene colloidal suspension is studied by thermal reducing graphene oxide in N-methylpyrrolidone (NMP) and γ-Butyrolactone (GBL) at 200°. Without assistance of polymeric or surfactant stabilizers, thermal reduction and dispersion of reduced graphene sheets are performed in one pot, and stable suspensions are confirmed by transmission electron microscope (TEM) and atomic force microscope (AFM) technic. Experimental results such as thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman indicate bulk cleavage of oxygen-containing functional groups and restoration of graphite structure on reduced graphene oxide sheets. The study contributes to the preparation of graphene-based nanocomposites using this quick and low-cost processing technique.

Photochemical Synthesis of Noble Metal (Ag, Pd, Au, Pt) on Graphene/ZnO Multihybrid Nanoarchitectures as Electrocatalysis for H2O2 Reduction

For the first time, a series of noble metal (Ag, Au, Pd, and Pt) nanoparticles (NPs) based on new functional graphene were successfully achieved via UV-assisted photocatalytic reduction by ZnO nanorods. The whole preparation strategy for constructing noble metal deposited graphene sheets/ZnO (GS/ZnO) was elucidated in detail in this work. First, graphene oxide based two-dimensional carbon nanostructures served as a support to disperse ZnO nanorods through a hydrothermal route. The ZnO nanorods were self-assembled onto the surface of graphene sheets, forming GS/ZnO nanocomposite, and the graphene oxide was reduced, yielding reduced graphene sheets in this synthetic procedure. Second, the GS/ZnO films were further employed as supporting materials for the dispersion of metal nanoparticles. Photogenerated electrons from UV-irradiated ZnO were transported across GS to stepwise and respectively reduce v μL metal ions (Ag(+), Pd(2+), AuCl4(-), PtCl6(2-), 20 mg/mL) into metal (Ag, Pd, Au, Pt) NPs at a location distinct from the ZnO anchored site, forming five graphene-based hybrid nanocomposites designated as GS/ZnO, GS/ZnO@Agv, GS/ZnO@Pdv, GS/ZnO@Auv, GS/ZnO@Ptv, respectively. The obtained mutihybrid nanoarchitectured materials were clearly characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). According to the diameters and distribution, the four metal NPs on GS/ZnO were divided into two categories: Ag&Au and Pd&Pt. Their difference was rooted in the rival abilities of gathering electron between graphene and different metal islands in the photochemical reduction process. The electrochemical behaviors of the five resultant hybrid nanocomposites were investigated in H2O2 as well as in potassium ferricyanide (Fe(CN)6(3-/4-)) and displayed distinct electrocatalytic activity.

Synthesis of reduced graphene oxide/ZnO nanorods composites on graphene coated PET flexible substrates

In this work, reduced graphene oxide (rGO)/ZnO nanorods composites were synthesized on graphene coated PET flexible substrates. Both chemical vapor deposition (CVD) graphene and reduced graphene oxide (rGO) films were prepared following by hydrothermal growth of vertical aligned ZnO nanorods. Reduced graphene sheets were then spun coated on the ZnO materials to form a three dimensional (3D) porous nanostructure. The morphologies of the ZnO/CVD graphene and ZnO/rGO were investigated by SEM, which shows that the ZnO nanorods grown on rGO are larger in diameters and have lower density compared with those grown on CVD graphene substrate. As a result of fact, the rough surface of nano-scale ZnO on rGO film allows rGO droplets to seep into the large voids of ZnO nanorods, then to form the rGO/ZnO hierarchical structure. By comparison of the different results, we conclude that rGO/ZnO 3D nanostructure is more desirable for the application of energy storage devices.

Thermodynamic and Structural Insights into Nanocomposites Engineering by Comparing Two Materials Assembly Techniques for Graphene

Materials assembled by layer-by-layer (LBL) assembly and vacuum-assisted flocculation (VAF) have similarities, but a systematic study of their comparative advantages and disadvantages is missing. Such a study is needed from both practical and fundamental perspectives aiming at a better understanding of structure-property relationships of nanocomposites and purposeful engineering of materials with unique properties. Layered composites from polyvinyl alcohol (PVA) and reduced graphene (RG) are made by both techniques. We comparatively evaluate their structure, mechanical, and electrical properties. LBL and VAF composites demonstrate clear differences at atomic and nanoscale structural levels but reveal similarities in micrometer and submicrometer organization. Epitaxial crystallization and suppression of phase transition temperatures are more pronounced for PVA in LBL than for VAF composites. Mechanical properties are virtually identical for both assemblies at high RG contents. We conclude that mechanical properties in layered RG assemblies are largely determined by the thermodynamic state of PVA at the polymer/nanosheet interface rather than the nanometer scale differences in RG packing. High and nearly identical values of toughness for LBL and VAF composites reaching 6.1 MJ/m(3) observed for thermodynamically optimal composition confirm this conclusion. Their toughness is the highest among all other layered assemblies from RG, cellulose, clay, etc. Electrical conductivity, however, is more than 10× higher for LBL than for VAF composites for the same RG contents. Electrical properties are largely determined by the tunneling barrier between RG sheets and therefore strongly dependent on atomic/nanoscale organization. These findings open the door for application-oriented methods of materials engineering using both types of layered assemblies.

Graphene-Patched CNT/MnO2Nanocomposite Papers for the Electrode of High-Performance Flexible Asymmetric Supercapacitors

MnO2 has been widely studied as the pseudo-capactive electrode material of high-performance supercapacitors for its large operating voltage, low cost, and environmental friendliness. However, it suffers from low conductivity and being hardly handle as the electrodes of supercapacitors especially with flexibility, which largely limit its electrochemical performance and application. Herein, we report a novel ternary composite paper composed of reduced graphene sheet (GR)-patched carbon nanotube (CNT)/MnO2, which has controllable structures and prominent electrochemical properties for a flexible electrode of the supercapacitor. The composite paper was prepared by electrochemical deposition of MnO2 on a flexible CNT paper and further adsorption of GR on its surface to enhance the surface conductivity of the electrode and prohibit MnO2 nanospheres from detaching with the electrode. The presence of GR was found remarkably effective in enhancing the initial electrochemical capacitance of the composite paper from 280 F/g to 486.6 F/g. Furthermore, it ensures the stability of the capacitance after a long period of charge/discharge cycles. A flexible CNT/polyaniline/CNT/MnO2/GR asymmetric supercapacitor was assembled with this composite paper as an electrode and aqueous electrolyte gel as the separator. Its operating voltage reached 1.6 V, with an energy density at 24.8 Wh/kg. Such a composite structure derived from a multiscale assembly can offer not only a robust scaffold loading MnO2 nanospheres but also a conductive network for efficient ionic and electronic transport; thus, it is potentially promising as a novel electrode architecture for high-performance flexible energy storage devices.

Low percolation threshold of graphene/polymer composites prepared by solvothermal reduction of graphene oxide in the polymer solution.

Graphene/polyvinylidene fluoride (PVDF) composites were prepared using in-situ solvothermal reduction of graphene oxide in the PVDF solution. The electrical conductivity of the composites was greatly improved by doping with graphene sheets. The percolation threshold of such composite was determined to be 0.31 vol.%, being much smaller than that of the composites prepared via blending reduced graphene sheets with polymer matrix. This is attributed to the large aspect ratio of the SRG sheets and their uniform dispersion in the polymer matrix. The dielectric constant of PVDF showed a marked increase from 7 to about 105 with only 0.5 vol.% loading of SRG content. Like the other conductor-insulator systems, the AC conductivity of the system also obeyed the universal dynamic response. In addition, the SRG/PVDF composite shows a much stronger nonlinear conduction behavior than carbon nanotube/nanofiber based polymer composite, owing to intense Zener tunneling between the SRG sheets. The strong electrical nonlinearity provides further support for a homogeneous dispersion of SRG sheets in the polymer matrix.

Phosphorus-Doped Exfoliated Graphene for Supercapacitor Electrodes

Graphene, a single atom thick carbon material with high surface area and electrical conductivity provides an ideal platform for designing high performance electrochemical devices. This paper reports the synthesis of phosphorous doped graphene from reduced graphene sheets, its characterization by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy and its use for supercapacitor applications. The specific capacitance was found to be 367 Fg(-1) from electrochemical measurements. These samples show a high power density of 9 kW kg(-1) and energy density of 59 Wh kg(-1) in an aqueous electrolyte solution, which is much higher than other graphene-based supercapacitors. The phosphorus-doped graphene showed a high potential for use in low cost energy storage devices.

Hierarchically porous hybrids of polyaniline nanoparticles anchored on reduced graphene oxide sheets as counter electrodes for dye-sensitized solar cells

Hierarchically porous polyaniline–reduced graphene oxide hybrids have been developed via oxidative polymerization of aniline by MnO2 on reduced graphene sheets under acidic conditions (named M-PANI@rGO). The formation mechanism of the above hybrids indicates that the MnO2 undergoes oxidative disintegration and results in the porous structure of polyaniline (PANI) nanoparticle formation on the reduced graphene oxide (rGO) surface. The scanning electron microscopy (SEM) images and Brunauer–Emmett–Teller (BET) nitrogen sorption–desorption measurement clearly showed the nanoporous nature of the M-PANI@rGO hybrids. TEM-EDX confirmed the complete removal/degradation of MnO2 during the oxidative polymerization of aniline. Just for comparison, PANI–rGO hybrids have also been prepared via conventional polymerization using (NH4)2S2O8 as the oxidant (named C-PANI@rGO). When these different architectural PANI@rGO hybrids were applied as the counter electrode for dye-sensitized solar cells (DSSCs), the short-circuit current density (Jsc) and power-conversion efficiency (η) of the DSSCs with C-PANI@rGO hybrids are measured to be 11.64 mA cm−2 and 5.62%, respectively, while the corresponding values are 12.88 mA cm−2 and 6.15% for the DSSCs with M-PANI@rGO hybrids, which is comparable to 6.73% for the cell with a Pt counter electrode under the same experimental conditions. The hierarchically porous M-PANI@rGO hybrid is thus a promising candidate to replace platinum as a counter electrode for DSSCs.

ZnO nanorods on reduced graphene sheets with excellent field emission, gas sensor and photocatalytic properties

In the flexible devices' fabrication, highly ordered nanoscale texturing such as semiconductor metal oxide nanorod arrays on the flexible substrates is critical for optimal performance. Herein, a simple and general hydrothermal route has been developed to result in a large-scale growth of ZnO nanorod arrays on double sides of the flexible reduced graphene sheets (rGss) forming sandwichlike heterostructures of ZnO/G/ZnO, and on a single side of the flexible rGss forming two-layered heterostructures of ZnO/G. The diameter and density of the ZnO nanorods grown on the rGss can be easily tuned as required by varying the seed-solution concentration. Due to the outstanding mechanical and electrical properties of the rGss, two-layered ZnO/G heterostructures were demonstrated to possess excellent field emission properties (turn-on field as low as 2.1 V μm−1, the emitting current ∼470 μA cm−2 at 3 V μm−1) and gas sensing (three times the ZnO nanorods); the sandwichlike ZnO/G/ZnO heterostructures have much higher photocatalytic activity under UV irradiation than those of ZnO nanorods and ZnO/G heterostructures, suggesting a promising candidate for photocatalytic decontamination. This would open up possibilities for the extensive study of the physical and chemical properties from these most promising nanostructures and extend their practical applications.