The Preparation of Compressible and Fire‐Resistant Sponge‐Supported Reduced Graphene Oxide Aerogel for Electromagnetic Interference Shielding

We here report a facile method to fabricate a sponge‐supported reduced graphene oxide aerogel (S‐RGOA) using a commercial melamine sponge and graphene oxide (GO). Firstly, GO sheets were self‐assembled within the melamine sponge by the assistance of a chemical cross‐linking agent; and then, freeze‐drying and thermal treatment were adopted to prepare S‐RGOA, in which continuous porous reduced graphene oxide (RGO) network formed between the skeleton. The resulting S‐RGOA exhibited a high electromagnetic interference shielding effectiveness (EMI SE) of 20.4‐27.3 dB in 8–12 GHz and the specific EMI SE could reach 1437 dB?cm³g^?1. The mechanical test suggests that the lightweight S‐RGOA is compressible and possesses low energy dissipation. Burning and TGA measurements indicate that S‐RGOA is fire‐resistant and has excellent thermal stability. Our work provides an economical and environmentally‐friendly method to fabricate RGO aerogels for using as electromagnetic interference materials.     

Electrochemical capacitors based on the composite of graphene and nickel foam

An improved Hummers method was developed for the simple and efficient production of high-quality graphene oxide(GO), and the composite of GO and nickel foam(NF)(GO/NF) was fabricated by ultrasonication-vacuum-assisted deposition of an aqueous solution of GO on NF. After chemical or thermal reduction, the composite of reduced GO and nickel foam(r GO/NF) was obtained. The electrochemical capacitance performance of r GO/NF was investigated using cyclic voltammetry and galvanostatic charge/discharge measurements. The chemically reduced r GO/NF composite(C-r GO/NF) exhibited high specific capacitance of 379 F/g at 1.0 A/g and 266.5 F/g at 10 A/g. We also prepared thermally reduced graphene oxide at 473 K in order to illuminate the difference in effect between the chemical and low-temperature thermal reduction methods on electrochemical properties. The cycling performance of thermally reduced r GO/NF composite(T-r GO/NF) and C-r GO/NF had ~91% and ~95% capacitance retention after 2000 cycles in a 6 mol/L KOH electrolyte, respectively. Electrochemical experiments indicated that the obtained r GO/NF has very good capacitive performance and could be used as a potential application of electrochemical capacitors. Our work revealed high electrochemical capacitor performance of r GO/NF composite and provided a facile method of r GO/NF preparation.     

Preparation of porous polyimide/in‐situ reduced graphene oxide composite films for electromagnetic interference shielding

Herein we report an easy and efficient approach to prepare lightweight porous polyimide (PI)/reduced graphene oxide (RGO) composite films. First, porous poly (amic acid) (PAA)/graphene oxide (GO) composite films were prepared via non‐solvent induced phase separation (NIPS) process. Afterwards PAA was converted into PI through thermal imidization and simultaneously GO dispersed in PAA matrix was in situ thermally reduced to RGO. The GO undergoing the same thermal treatment process as thermal imidization was characterized with thermogravimetric analysis, Raman spectra, X‐ray photoelectron spectroscopy and X‐ray diffraction to demonstrate that GO was in situ reduced during thermal imidization process. The resultant porous PI/RGO composite film (500‐µm thickness), which was prepared from pristine PAA/GO composite with 8 wt% GO, exhibited effective electrical conductivity of 0.015 S m^?1 and excellent specific shielding efficiency value of 693 dB cm² g^?1. In addition, the thermal stability of the porous PI/RGO composite films was also dramatically enhanced. Compared with that of porous PI film, the 5% weight loss temperature of the composite film mentioned above was improved from 525°C to 538°C. Moreover, tensile test showed that the composite film mentioned above possessed a tensile strength of 6.97 MPa and Young's modulus of 545 MPa, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Conducting polystyrene/polyaniline blend through template-assisted emulsion polymerization

Electrically conducting polystyrene (PS)/polyaniline blends have been prepared through a one-step “anilinium-surfactant template”-assisted emulsion polymerization at room temperature. The self-assembled cylindrical An⁺PDPSA^? micelle formed inside the PS matrix can act as a structure directing template cum dopant. Morphological observation under scanning electron microscopic studies revealed that during the progress of polymerization, the initially formed nanostructured conducting polyaniline was changed into cubic/hexagonal/lamellar particles and finally transformed into a percolated structure inside the PS matrix. Blend was further characterized by UV-Vis spectroscopy, FTIR spectroscopy, X-ray diffraction, electrical conductivity, thermal stability, dielectric property, rheological property, and electromagnetic shielding efficiency. The key finding of this work is that the conductive blend prepared through micelle-guided polymerization exhibited superior electrical conductivity (9.6 S/m) with low percolation threshold concentration (5 wt%), excellent thermal stability, electromagnetic interference (EMI) SE of 1–10 dB which makes it a promising candidate for EMI shielding and antistatic discharge matrix for the encapsulation of microelectronic devices.     

Activated carbon/graphene composites with high-rate performance as electrode materials for electrochemical capacitors

Glucose-derived activated carbon (GAC)/reduced graphene oxide (RGO) composites are prepared by pre-carbonization of the precursors (aqueous mixture of glucose and graphene oxide) and KOH activation of the pyrolysis products. The effect of the mass ratio of graphene oxide (GO) in the precursor on the electrochemical performance of GAC/RGO composites as electrode materials for electrochemical capacitors is investigated. It is found that the thermally reduced graphene oxide sheets serves as a wrinkled carrier to support the activated carbon particles after activation. The pore size distribution and surface area are depended on the mass ratio of GO. Besides, the rate capability of GAC is improved by the introduction of GO in the precursor. The highest specific capacitance of 334 F g^?1 is achieved for the GAC/RGO composite prepared from the precursor with a GO mass ratio of 3 %.     

Effect of carbonaceous support between graphite oxide and reduced graphene oxide with anchored Co<Subscript>3</Subscript>O<Subscript>4</Subscript> microspheres as electrode-active materials in a solid-state electrochemical capacitor

Hydrothermally synthesized Co₃O₄ microspheres were anchored to graphite oxide (GO) and thermally reduced graphene oxide (rGO) composites at different cobalt weight percentages (1, 10, and 100 wt%). The composite materials served as the active materials in bulk electrodes for two-electrode cell electrochemical capacitors (ECCs). GO/Co₃O₄–1 exhibited a high energy density of 35 W kg^?1 with a specific capacitance (C _sp) of 196 F g^?1 at a maximum charge density of 1 A g^?1. rGO/Co₃O₄-100 presented high specific power output values of up to 23.41 kW h kg^?1 with linear energy density behavior for the charge densities applied between 0.03 and 1 A g^?1. The composite materials showed Coulombic efficiencies of 96 and 93 % for GO/Co₃O₄–1 and rGO/Co₃O₄–100 respectively. The enhancement of capacitive performance is attributed to the oxygenated groups in the GO ECC and the specific area in the rGO ECC. These results offer an interesting insight into the type of carbonaceous support used for graphene derivative electrode materials in ECCs together with Co₃O₄ loading to improve capacitance performance in terms of specific energy density and specific power.

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Superior Lithium‐Ion Storage Properties of Mesoporous CuO–Reduced Graphene Oxide Composite Powder Prepared by a Two‐Step Spray‐Drying Process

Mesoporous CuO–reduced graphene oxide (rGO) composite powders were prepared by using a two‐step spray‐drying process. In the first step, hollow CuO powders were prepared from a spray solution of copper nitrate trihydrate with citric acid and were wet milled to obtain a colloidal spray solution. In the second step, spray drying of the colloidal solution that contained dispersed GO nanosheets produced mesoporous CuO–rGO composite powders with particle sizes of several microns. Thermal reduction of GO nanosheets to rGO nanosheets occurred during post‐treatment at 300 °C. Initial discharge capacities of the hollow CuO, bare CuO aggregate, and CuO–rGO composite powders at a current density of 2 A g^?1 were 838, 1145, and 1238 mA h g^?1, respectively. Their discharge capacities after 200 cycles were 259, 380, and 676 mA h g^?1, respectively, and their corresponding capacity retentions measured from the second cycle were 67, 48, and 76 %, respectively. The mesoporous CuO–rGO composite powders have high structural stability and high conductivity because of the rGO nanosheets, and display good cycling and rate performances.     

Towards efficient electromagnetic interference shielding performance for polyethylene composites by structuring segregated carbon black/graphite networks

An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.     

Flower-like SnO2 nanoparticles grown on graphene as anode materials for lithium-ion batteries

Tin oxide (SnO₂)/graphene composite was synthesized from SnCl₂?·?2H₂O and graphene oxide (GO) by a wet chemical-hydrothermal route. The GO was reduced to graphene nanosheet (GNS) and flower-like SnO₂ nano-crystals with size about 40 nm were homogeneously distributed on the surface of GNS. The SnO₂/graphene composites delivered a superior first discharge capacity of 1941.9 mAhg^?1 with a reversible capacity of 901.7 mAhg^?1 at the current density of 100 mAg^?1. Moreover, even at higher densities of 200 and 500 mAg^?1, the SnO₂/graphene composite still maintained enhanced cycling stability. After 40 cycles, the discharge capacity was still maintained at 691.1 mAhg^?1 at the current density of 100 mAg^?1. The SnO₂/graphene composite displayed an outstanding Li-battery performance with large reversible capacity and enhanced rate performance, which can be attributed to the highly uniform distribution of SnO₂ nanoparticles and high reduction degree of graphene. This result strongly indicates that the SnO₂/graphene composite was a promising anode material in high-performance lithium-ion batteries.     

Evaluation of graphene oxide and reduced graphene oxide in the immobilization of laccase enzyme and its application in the determination of dopamine

Bioelectrodes were developed based on a simple deposition of graphene oxide (GO) or reduced graphed oxide (rGO) and laccase (Lac) on a glassy carbon (GC) electrode surface. The morphology and electrochemical behavior of the biosensors were characterized by scanning electron microscopy and cyclic voltammetry. These results demonstrated that only rGO was successfully applied for the immobilization of the laccase enzyme, improving the analytical signal for the determination of dopamine. The GC/rGO/Lac biosensor was applied to the detection of dopamine in synthetic urine and plasmatic serum samples, achieving a detection limit of 91.0 nmol L^?1.     

Low‐Temperature Solid‐State Microwave Reduction of Graphene Oxide for Transparent Electrically Conductive Coatings on Flexible Polydimethylsiloxane (PDMS)

Microwaves (MWs) are applied to initialize deoxygenation of graphene oxide (GO) in the solid state and at low temperatures (～165 °C). The Fourier‐transform infrared (FTIR) spectra of MW‐reduced graphene oxide (rGO) show a significantly reduced concentration of oxygen‐containing functional groups, such as carboxyl, hydroxyl and carbonyl. X‐ray photoelectron spectra confirm that microwaves can promote deoxygenation of GO at relatively low temperatures. Raman spectra and TGA measurements indicate that the defect level of GO significantly decreases during the isothermal solid‐state MW‐reduction process at low temperatures, corresponding to an efficient recovery of the fine graphene lattice structure. Based on both deoxygenation and defect‐level reduction, the resurgence of interconnected graphene‐like domains contributes to a low sheet resistance (～7.9×10⁴ Ω per square) of the MW‐reduced GO on SiO₂‐coated Si substrates with an optical transparency of 92.7 % at ～547 nm after MW reduction, indicating the ultrahigh efficiency of MW in GO reduction. Moreover, the low‐temperature solid‐state MW reduction is also applied in preparing flexible transparent conductive coatings on polydimethylsiloxane (PDMS) substrates. UV/Vis measurements indicate that the transparency of the thus‐prepared MW‐reduced GO coatings on PDMS substrates ranges from 34 to 96 %. Correspondingly, the sheet resistance of the coating ranges from 10⁵ to 10⁹ Ω per square, indicating that MW reduction of GO is promising for the convenient low‐temperature preparation of transparent conductors on flexible polymeric substrates.     

Multi-layered graphene-Fe3O4/poly (vinylidene fluoride) hybrid composite films for high-efficient electromagnetic shielding

A flexible and multi-layered graphene nanosheets (GNSs)-Fe₃O₄/poly (vinylidene fluoride) hybrid composite film with high-efficient electromagnetic interference (EMI) shielding was fabricated via a facile layer-by-layer coating. The well-designed multi-layered and hybrid electromagnetic fillers endow the prepared film with good surface impedance matching and prominent internal multiple absorption, which forms “absorb-reflect-reabsorb” electromagnetic transmission pattern and results in highly efficient electromagnetic shielding effectiveness (EMI SE). The resultant composite film exhibits an exceptional EMI SE of 52.0 dB at a thickness of 0.3 mm. What is more important is that the prepared film exhibits excellent flexibility and EMI stability, and the retention rate of efficient EMI SE is high as 91.9% after 1000 bending-release cycles. This study provides a feasible strategy for designing high-efficient EMI shielding film with excellent flexibility and ultra-thin thickness that suitable for next-generation intelligent protection devices.     

Core–Shell LiFePO4/Carbon‐Coated Reduced Graphene Oxide Hybrids for High‐Power Lithium‐Ion Battery Cathodes

Core‐shell carbon‐coated LiFePO₄ nanoparticles were hybridized with reduced graphene (rGO) for high‐power lithium‐ion battery cathodes. Spontaneous aggregation of hydrophobic graphene in aqueous solutions during the formation of composite materials was precluded by employing hydrophilic graphene oxide (GO) as starting templates. The fabrication of true nanoscale carbon‐coated LiFePO₄‐rGO (LFP/C‐rGO) hybrids were ascribed to three factors: 1) In‐situ polymerization of polypyrrole for constrained nanoparticle synthesis of LiFePO₄, 2) enhanced dispersion of conducting 2D networks endowed by colloidal stability of GO, and 3) intimate contact between active materials and rGO. The importance of conducting template dispersion was demonstrated by contrasting LFP/C‐rGO hybrids with LFP/C‐rGO composites in which agglomerated rGO solution was used as the starting templates. The fabricated hybrid cathodes showed superior rate capability and cyclability with rates from 0.1 to 60 C. This study demonstrated the synergistic combination of nanosizing with efficient conducting templates to afford facile Li⁺ ion and electron transport for high power applications.     

Electrochemistry-assisted microstructuring of reduced graphene oxide-based microarrays with adjustable electrical behavior

An electrochemistry-assisted microstructuring process is developed for fabricating well-aligned reduced graphene oxide (rGO)-based micropatterns on arbitrary substrates using a combined method of photolithography, electrochemical reduction and wet etching techniques. The dimension of special-shaped rGO microarrays localized in an insulating GO matrix is effectively adjusted by changing GO reduction time without multi-mask patterning. The increased conductivity of rGO micropatterns by several orders of magnitude is achieved by controlling GO thickness and reduction time. The electrochemical activity of rGO micropatterns as microarray electrodes is confirmed by using ferricyanide in aqueous solution as the redox probe. The present method could be a scalable technology to conventional photolithography for fabricating arbitrary rGO micropatterns in an insulating GO matrix for their potential applications in next generation electronic and electrochemical devices.     

Electrically conductive carbon nanofiber/polyethylene composite: effect of melt mixing conditions

The effect of melt mixing conditions on the morphological, rheological, electrical, electromagnetic interference (EMI) shielding effectiveness (SE), and tensile properties of 7.5 vol% vapor grown carbon nanofiber (VGCNF)/polyethylene composites were investigated. 7.5 vol% VGCNF was used because such loading is required to obtain a composite with satisfactory EMI SE. The composites were compounded by melt mixing and the parts were prepared by hot‐compression molding. The dispersion and distribution of nanofibers were enhanced by increasing the mixing energy, i.e. mixing time and/or rotation speed. The influence of mixing energy on the electrical and EMI SE properties was found to be a function of rotation speed, i.e. shear stress. For composites compounded at 20 rpm, increasing the mixing energy from 70 to 2300 J/ml decreased the EMI SE from 29.5 to 23.9 dB. However, for composites prepared at 100 rpm, increasing the mixing energy from 600 to 1700 J/ml decreased the EMI SE from 25.4 to 18.6 dB. No considerable influence on the yield stress, Young's modulus, and strain at break were found for different processing conditions. Copyright © 2009 John Wiley & Sons, Ltd.     

Free‐standing Graphene/Poly(methylene blue)/AgNPs Composite Paper for Electrochemical Sensing of NADH

Highly flexible graphene/poly(methylene blue)/AgNPs composite paper was successfully prepared for amperometric biosensing of NADH. For this purpose, a dispersion including graphene oxide (GO), methylene blue (MB) and silver nanoparticles (AgNPs) was prepared and GO/MB/AgNPs paper was acquired by vacuum‐filtration of this dispersion through a suitable membrane. After peeling it off from membrane, it was transformed to rGO/MB/AgNPs paper by performing reduction with hydriodic acid. In a three‐electrode cell, which is containing 0.1 M phosphate buffer solution (pH: 9.0), rGO/MB/AgNPs paper was used as working electrode and rGO/poly(MB)/AgNPs composite paper was generated by surface‐confined electropolymerization of MB using successive cyclic voltammetry approach in a suitable potential window. Characterization of this composite paper was carried out by using scanning electron microscopy, scanning tunneling microscopy, X‐ray photoelectron spectroscopy, powder X‐ray diffraction spectroscopy, Raman spectroscopy, four‐point probe conductivity measurement and cyclic voltammetry techniques. Flexible rGO/poly(MB)/AgNPs composite paper has demonstrated high sensitivity, wide linear range and low detection limit for amperometric quantification of NADH.     

A novel ε-HNIW-based insensitive high explosive incorporated with reduced graphene oxide

A novel ε-HNIW-based explosive formula with low sensitive and high energy was developed by systematically researching the processes of recrystallization, granularity gradation, and coating of ε-HNIW and option of energetic deterrents. The grain size and morphology of HNIW crystals were modified by solvent/antisolvent recrystallization. The ε-HNIW particles were graded and coated by emulsion polymerization method with 551 glue. The binder reduced the mechanical sensitivity of ε-HNIW significantly and showed good compatibility with ε-HNIW, but also weakened the decomposition enthalpy. With the purpose of developing new energetic deterrents in insensitive high explosive formulations, novel carbon materials graphene oxide (GO) and reduced graphene oxide (rGO) were prepared and incorporated in plastic-bonded explosive (PBX) formulations. For comparison, the effects of conventional deterrent flake graphite were also involved. It turned out that the mechanical sensitivities of ε-HNIW/551 glue have all reduced to some extent with the incorporation of graphite, GO, and rGO. Flake graphite induced the PBX decompose earlier slightly and weaken the heat output. The addition of GO resulted in noticeable antedating decomposition of ε-HNIW/551 glue although remarkably increased the decomposition heat. The formula of ε-HNIW/551 glue/rGO provided a moderate growth in decomposition heat and best thermal stability. In slow cook-off tests, the formulas of ε-HNIW/551 glue and ε-HNIW/551 glue/rGO showed good thermal stability and might be qualified to apply safely under 200 °C. Comprehensively considering the mechanical sensitivity, thermals stability, energy performance, and practical application, ε-HNIW/551 glue/rGO is supposed to be an eligible insensitive high-energy PBX formula.     

Enhancing Hematite Photoanode Activity for Water Oxidation by Incorporation of Reduced Graphene Oxide

Two effective methods to prepare reduced graphene oxide (rGO)/hematite nanostructured photoanodes and their photoelectrochemical characterization towards water splitting reactions are presented. First, graphene oxide (GO) is reduced to rGO using hydrazine in a basic solution containing tetrabutylammonium hydroxide (TBAOH), and then deposited over the nanostructured hematite photoanodes previously treated at 750 °C for 30 min. The second method follows the deposition of a paste containing a mixture of hematite nanoparticles and rGO sheets by the doctor‐blade method, varying the rGO concentration. Since hematite suffers from low electron mobility, a low absorption coefficient, high recombination rates and slow reaction kinetics, the incorporation of rGO in the hematite can overcome such limitations due to graphene's exceptional properties. Using the first method, the rGO incorporation results in a photocurrent density increase from 0.56 to 0.82 mA cm^?2 at 1.23 V_RHE. Our results indicate that the rGO incorporation in the hematite photoanodes shows a positive effect in the reduction of the electron–hole recombination rate.     

Flexible poly(dimethyl siloxane) composites enhanced with 3D porous interconnected three-component nanofiller framework for absorption-dominated electromagnetic shielding

A new poly(dimethyl siloxane) (PDMS) composite was developed based on the 3D porous interconnected framework that is fabricated from reduced graphene oxide (rGO) and Dy₂O₃ decorated single-walled carbon nanotube (Dy₂O₃@SWNT). Despite merely containing ~0.6 wt% fillers, the composite prepared by backfilling 3D framework (3D-Dy₂O₃@SWNT-rGO) with PDMS prepolymer acquires as high as 32.9 dB of absorption-dominated (92.3%–96.9%) electromagnetic interference (EMI) shielding effectiveness in X-band, and up to 47% and 52% increments of respective compressive strength and modulus at 50% strain relative to PDMS. These performances result from the excellent combination of electrical conductivity (up to 0.317 S cm⁻¹), magnetism (up to 7.1 × 10⁻⁵ emu g⁻¹ of susceptibility), and mechanical toughness (complete recovery after 80% compression) in a single three-component filler system of 3D-Dy₂O₃@SWNT-rGO. Moreover, the organic integration of mechanical flexibility of PDMS with shape-tunable ability of 3D-Dy₂O₃@SWNT-rGO enables PDMS composites developed here to EMI-shield any shape surfaces.     

Preparation of silver/graphene/polymer hybrid microspheres and the study of photocatalytic degradation

Three-dimensional silver/graphene/polymer hybrid microspheres were prepared to depress the aggregation of two-dimensional graphene. Graphene oxide (GO) sheets were successfully wrapped on the surface of amine-functionalized polystyrene-poly (glycidyl methacrylate) (PS-PGMA) microspheres (～3 μm in diameter) to form graphene oxide/amino-microsphere (GO/AMS) core–shell structure. Subsequently, the wrapped GO sheets were reduced by using hydrazine hydrate as the reducing agents, meanwhile decorated with silver nanoparticles on the wrinkled surface to form Ag-rGO/AMS hybrid microspheres with monodisperse distributions in shape and diameter. The resulting materials were characterized by power X-ray diffraction, scanning electron microscope, Raman spectra, and ultraviolet–visible (UV–vis) absorption spectra. Since Ag nanoparticles behave surface plasmon resonance effect and rGO structure can improve the separation of photogenerated electrons and holes, the Ag-rGO/AMS composites present good photocatalytic activities for the degradation of methylene blue (MB) as 93 % MB were degraded after 2.5 h under irradiation.