Conversion of pencil graphite to graphene/polypyrrole nanofiber composite electrodes and its doping effect on the supercapacitive properties

Graphene platelets were synthesized from pencil flake graphite and commercial graphite by chemical method. The chemical method involved modified Hummer's method to synthesize graphene oxide (GO) and the use of hydrazine monohydrate to reduce GO to reduced graphene oxide (rGO). rGO were further reduced using rapid microwave treatment in presence of little amount of hydrazine monohydrate to graphene platelets. Chemically modified graphene/polypyrrole (PPy) nanofiber composites were prepared by in situ anodic electropolymerization of pyrrole monomer in the presence of graphene on stainless steel substrate. The morphology, composition, and electronic structure of the composites together with PPy fibers, graphene oxide (GO), rGO, and graphene were characterized using X‐ray diffraction (XRD), laser‐Raman, and scanning electron microscopic (SEM) methods. From SEM, it was observed that chemically modified graphene formed as a uniform nanocomposite with the PPy fibers absorbed on the graphene surface and/or filled between the graphene sheets. Such uniform structure together with the observed high conductivities afforded high specific capacitance and good cycling stability during the charge–discharge process when used as supercapacitor electrodes. A specific capacitance of supercapacitor was as high as 304 F g^?1 at a current density of 2 mA cm^?1 was achieved over a PPy‐doped graphene composite. POLYM. ENG. SCI., 55:2118–2126, 2015. © 2014 Society of Plastics Engineers     

Electrical conductivity studies on water‐soluble polypyrrole–graphene oxide composites

Polypyrrole (PPy)–graphene oxide (GO) composites are synthesized via a soft‐chemical in situ method at different GO concentrations (10, 20, 30, 40, and 50 wt%) and with ammonium persulfate (APS) as the oxidant. The synthesized composites were characterized using Fourier transform infrared (FTIR) and ultraviolet‐visible light (UV–vis) spectroscopic studies, and their surface properties were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Characterization and surface morphology results indicate that PPy is adsorbed onto the graphene surfaces and/or fills the GO sheets. The temperature‐dependent DC conductivity of the polymer composite films in the 300–500 K range indicates a semiconducting behavior with increasing GO concentration in the PPy polymer. Based on morphological and conductivity studies, the large surface area and high aspect ratio of the in situ‐generated GO may have played an important role in the noticeable improvement in the electrical conductivity of the prepared composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Synthesis of polypyrrole-reduced graphene oxide composites by in-situ photopolymerization and its application as a supercapacitor electrode

A highly conductive polypyrrole (PPy)-reduced graphene oxide (RGO) composite with an electrical conductivity of 610 S m⁻¹ was successfully synthesized by the in-situ photopolymerization of pyrrole in a graphene oxide suspension. Graphene oxide (GO) played the role of an electron acceptor and was reduced as it accepted electrons. The reduction of GO was confirmed by the increase in the C/O ratio of RGO with the UV irradiation time as well as the high electrical conductivity of PPy-RGO composite. Through the thermogravimetric analysis, it has been found that the PPy-RGO composite exhibited high thermal stability compared to the GO and PPy. This material was used as an electrode in a supercapacitor cell and showed excellent performance for electrical energy storage. The composite exhibited a specific capacitance of 376 F g⁻¹ at a scan rate of 25 mV s⁻¹.     

Polypyrrole coated graphene nanoplatelets and the effect of rare earth ions with nanocomposites

PPy/graphene/rare earth ions (PPy/GR/La³⁺, PPy/GR/Sm³⁺, PPy/GR/Eu³⁺, PPy/GR/Gd³⁺ and PPy/GR/Tb³⁺) are fabricated via in-situ polymerization using p-toluenesulfonic acid as a dopant and FeCl₃ as an oxidant. The surface morphology of the PPy/GR/La³⁺, PPy/GR/Sm³⁺, PPy/GR/Eu³⁺, PPy/GR/Gd³⁺ and PPy/GR/Tb³⁺ composites were characterized by using transmission electron microscopy. The maximum conductivity of PPy/GR/La³⁺, PPy/GR/Sm³⁺, PPy/GR/Eu³⁺, PPy/GR/Gd³⁺ and PPy/GR/Tb³⁺ composites found with 1 wt.% GR and 2 wt.% La³⁺, Sm³⁺, Eu³⁺, Gd³⁺ and Tb³⁺ at room temperature.     

Synthesis,characterization and supercapacitors of electrically conductive PPy/graphene/rare earth ions composites

PPy/graphene/rare earth ions (PPy/GR/RE³⁺) were prepared using an in situ chemical polymerization of the monomer in the presence of FeCl₃ oxidant and p-toluenesulfonic acid dopant. The PPy/GR/RE³⁺ composites were characterized by FT-IR spectroscopy, four-point probe conductivity, scanning electron microscopy and transmission electron microscopy. The maximum conductivity of PPy/GR/Gd³⁺ composites is about 9.71 S/cm found with 1 wt% GR and 2 wt% Gd³⁺ at room temperature. The capacitance of the composite electrodes was investigated with cyclic voltammetry. As results of this study, the PPy/GR/Gd³⁺ was effective to obtain fully reversible and very fast faradaic reaction. Hence, the PPy/GR/Gd³⁺ could contribute to the pseudo-capacitive charge storage. The PPy/GR/Gd³⁺ exhibited higher specific capacitance of ~238 F/g at 1 A/g current density. Thermal gravimetric analysis demonstrates an improved thermal stability of PPy in the PPy/GR/Gd³⁺ composites.     

One‐pot synthesis,characterization, and field emission investigations of composites of polypyrrole with graphene oxide,reduced graphene oxide,and graphene nanoribbons

Pyrrole monomer was polymerized by a chemical oxidative route in the presence of graphene oxide (GO), reduced GO (rGO), and graphene nanoribbons (GNR) separately to prepare composites of polypyrrole (PPy) as PPy–GO, PPy–rGO, and PPy–GNR, respectively. The morphological, chemical, and structural characterization of the as‐synthesized products was carried out using scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. Field emission studies of the PPy–GO, PPy–rGO, and PPy–GNR emitters were performed at the base pressure of 1 × 10^?8 mbar in a planar “diode” configuration. The turn‐on field values, corresponding to an emission current density of 1 µA/cm², are observed to be 1.5, 2.2, and 0.9 V/µm for the PPy–GO, PPy–rGO, and PPy–GNR emitters, respectively. The maximum emission current density of 2.5 mA/cm² is drawn from PPy–GO at an applied electric field of 3.2 V/µm, 1.2 mA/cm² at 3.6 V/µm from the PPy–rGO, and 8 mA/cm² at 2.2 V/µm from the PPy–GNR emitters. All of the composites exhibit good emission stability over more than 2 h. The results indicate the potential for a facile route for synthesizing composites of conducting polymers and graphene‐based materials, with enhanced functionality. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45170.     

Graphene nanosheets-polypyrrole hybrid material as a highly active catalyst support for formic acid electro-oxidation

A novel electrode material based on graphene oxide (GO)-polypyrrole (PPy) composites was synthesized by in situ chemical oxidation polymerization. Palladium nanoparticles (NPs) with a diameter of 4.0 nm were loaded on the reduced graphene oxide(RGO)-PPy composites by a microwave-assisted polyol process. Microstructure analysis showed that a layer of coated PPy film with monodisperse Pd NPs is present on the RGO surface. The Pd/RGO-PPy catalysts exhibit excellent catalytic activity and stability for formic acid electro-oxidation when the weight feed ratio of GO to pyrrole monomer is 2:1. The superior performance of Pd/RGO-PPy catalysts may arise from utilization of heterogeneous nucleation sites for NPs and the greatly increased electronic conductivity of the supports.     

Graphene‐based composite with microwave absorption property prepared by in situ reduction

Binary composite of graphene/poly(ethylene oxide) (PEO) with microwave absorption property is prepared by in situ reduction process. Graphite oxide (GO) is prepared from flake graphite by modified Hummers' method and further dispersed in distilled water to get GO solution. Then, PEO powder is slowly added into GO solution to get GO/PEO solution, and graphene/PEO composites is prepared via a facile and quick reduction process in GO/PEO solution. PEO and graphene/PEO composites are characterized by scanning electron microscopy, atomic force microscopy, thermo gravimetric analysis, and vector network analyzer. The results show that graphene is uniformly dispersed in PEO matrix because GO and PEO can be uniformly dispersed at molecular level due to their water‐solubility and the agglomeration of graphene can be prevented by PEO macromolecular chains during in situ reduction process. Graphene/PEO composite has better thermal stability than PEO, which can be explained by the graphene restoration of sp² bonded carbon structure. Meanwhile, graphene/PEO composite shows excellent microwave absorption property at low grapheme content. The minimum reflection loss of graphene/PEO composite is up to −20.0 dB when the content of graphene is only 1 wt%. POLYM. COMPOS., 35:461–467, 2014. © 2013 Society of Plastics Engineers     

Electrochemically synthesized graphene/polypyrrole composites and their use in supercapacitor

Composite films consisting of polypyrrole (PPy) and graphene oxide (GO) were electrochemically synthesized by electrooxidation of 0.1 M pyrrole in aqueous solution containing appropriate amounts of GO. Simultaneous chronoamperometric growth profiles and frequency changes on a quartz crystal microbalance showed that the anionic GO was incorporated in the growing GO/PPy composite to maintain its electrical neutrality. Subsequently, the GO was reduced electrochemically to form a reduced GO/PPy (RGO/PPy) composite by cyclic voltammetry. Specific capacitances estimated from galvanostatic discharge curves in 1 M H₂SO₄ at a current density of 1 A g^?1 indicated that values for the RGO/PPy composite were larger than those of a pristine PPy film and the GO/PPy composite. In the case of 6 mg mL^?1 GO for the preparation of GO/PPy, a high specific capacitance of 424 F g^?1 obtained at the electrochemically prepared RGO/PPy composite indicated its potential for use as an electrode material for supercapacitors.     

Unusual functionalization of reduced graphene oxide for excellent chemical surface-enhanced Raman scattering by coupling with ZnO

A low-cost noble metal-free substrate comprised of annealed graphene oxide (GO)/ZnO composites is prepared to demonstrate an efficient chemical surface-enhanced Raman scattering effect. A high enhancement factor of about 10⁴, better than those reported for reduced GO (rGO)/Au and GO/Ag composites, is mainly attributed to the unusually abundant oxygen-containing groups generated on surface of rGO by coupling with ZnO nanoparticles at moderate temperature. High-resolution transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy are employed to examine the evolution of ZnO as well as reduction and functionalization of GO after different heat treatments.     

高电活性石墨烯/聚苯胺纳米复合材料的制备和表征

采用了一种简单有效地方法制备了高电活性的石墨烯/聚苯胺复合材料。首先,将苯胺在氧化石墨烯（GO）的水性分散液中氧化聚合,制备了氧化石墨烯/聚苯胺（GO/PANI）,再将GO/PANI与水合肼反应,制得还原-氧化石墨烯/聚苯胺（R（GO/PANI））。利用透射电子显微镜（TEM）,热失重分析（TGA）和循环伏安法（CV）对GO/PANI和R（GO/PANI的形貌,热稳定性和电化学性能进行了分析研究。结果表明,GO表面存PANI,且R（GO/PANI）的热稳定性和电活性都明显高于GO/PANI。     

Flexible Supercapacitor Based on Inkjet‐Printed Graphene@Polyaniline Nanocomposites with Ultrahigh Capacitance

This work describes the fabrication of high‐performance all‐solid‐state supercapacitors based on covalently‐anchored reduced graphene oxide (RGO)@polyaniline (PANI) composites via an inkjet printing method. Morphological and chemical characterization data show that PANI nanoparticles are immobilized on graphene oxide (GO) nanosheets via covalent bonds. Sandwich‐structured and interdigitated supercapacitors are fabricated by printing the as‐prepared GO@PANI composites on flexible substrates, followed by a chemical reduction. The devices display high volumetric capacitances (258.5 F cm^?3 at 1 mV s^?1 for sandwich‐structured ones and 554 F cm^?3 at 1 mV s^?1 for interdigitated ones) and excellent cycling retention (2000 cycles >90%). Moreover, at the bending state, there are no significant changes on the device capacitances, indicating their great flexibility. The high‐performance devices can be further designed to produce special geometries and patterns. The work may provide a novel strategy to fabricate RGO@PANI composite‐based supercapacitors, which allows the end users to precisely deposit active materials according to their designs, for miniature and wearable electronics.     

石墨烯复合功能材料及其在重金属离子检测的电化学研究与应用

石墨烯(GR)是典型的单原子碳纳米材料,具有独特的二维共辄平面结构,其高活性的比表面积和突出的导电性能,在电催化和敏感材料制备领域已得到广泛的应用。氧化石墨烯(GO)作为GR的前驱体,存在大量的含氧官能团,具有良好的水溶分散性。大量GO含氧官能团的介入会破坏其K-7T共辘结构,导致其电学性能变差。GO通过化学、水热合成或直接电化学还原方法可有效修复其共辄平面结构,得到导电性良好的还原氧化石墨烯(rGO),即GR.单组分的GR材料在实际应用中仍存在某些局限性,如电学活性相对较弱,与其它材料加工复合性能较差等。将GR、G O材料与其它功能材料进行复合,可进一步改善复合物的物理或化学性能,如分散性、加工修饰和电催化活性等。综述了石墨烯材料与金属及其氧化物纳米粒子、聚合物、掺杂原子、导电离子液体、碳纳米材料等功能材料复合后,能形成可调控的微结构,具有改性的化学性质和协同发挥的电学效应,表现出显著的电子传递能力及其功能性作用。论述了GR功能化修饰的复合材料作为敏感界面,构筑基于重金属离子检测的电化学生物传感器,可以实现对Pb2+,Hg2+,C『+等多种重金属离子的同时或分别检出,提出了GR复合制备材料的纳米结构特征、功能修饰作用对于提高传感器的电催化活性和选择性性能等方面的应用,并对该研究领域进行了总结与展望。     

Synthesis of conducting graphene/Si3N4 composites by spark plasma sintering

Graphene/silicon nitride (Si₃N₄) composites with high fraction of few layered graphene are synthesized by an in situ reduction of graphene oxide (GO) during spark plasma sintering (SPS) of the GO/Si₃N₄ composites. The adequate intermixing of the GO layers and the ceramic powders is achieved in alcohol under sonication followed by blade mixing. The reduction of GO occurs together with the composite densification in SPS, thus avoiding the implementation of additional reduction steps. The materials are studied by X-ray photoelectron and micro-Raman spectroscopy, revealing a high level of recovery of graphene-like domains. The SPS graphene/Si₃N₄ composites exhibit relatively large electrical conductivity values caused by the presence of reduced graphene oxide (∼1 S cm⁻¹ for ∼4 vol.%, and ∼7 S cm⁻¹ for 7 vol.% of reduced-GO). This single-step process also prevents the formation of highly curved graphene sheets during the thermal treatment as the sheets are homogeneously embedded in the ceramic matrix. The uniform distribution of the reduced GO sheets in the composites also produces a noticeable grain refinement of the silicon nitride matrix.     

Facile synthesis of reduced graphene oxide/MWNTs nanocomposite supercapacitor materials tested as electrophoretically deposited films on glassy carbon electrodes

This paper reports on a facile synthesis method for reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWNTs) nanocomposites. The initial step involves the use of graphene oxide to disperse the MWNTs, with subsequent reduction of the resultant graphene oxide/MWNTs composites using l-ascorbic acid (LAA) as a mild reductant. Reduction by LAA preserves the interaction between the rGO sheets and MWNTs. The dispersion-containing rGO/MWNTs composites was characterized and electrophoretically deposited anodically onto glassy carbon electrodes to form high surface area films for capacitance testing. Pseudo capacitance peaks were observed in the rGO/MWNTs composite electrodes, resulting in superior performance with capacitance values up to 134.3 F g^?1 recorded. This capacitance value is higher than those observed for LAA-reduced GO (LAA-rGO) (63.5 F g^?1), electrochemically reduced GO (EC-rGO) (27.6 F g^?1), or electrochemically reduced GO/MWNTs (EC-rGO/MWNTs) (98.4 F g^?1)-based electrodes.     

Glass fiber coated with graphene constructed through electrostatic self‐assembly and its application in poly(lactic acid) composite

A method to construct glass fiber/graphene material via the electrostatic self‐assembly was proposed. The graphene oxide (GO) nanosheets were firstly prepared from graphite according to Hummer's methods. Oppositely charged GO is successfully introduced to the surface of the GF cationized by 3‐aminopropyltriethoxysilane (APTES) treatment in the solution with mild agitation. Sequently, glass fibers coated with graphene (GF/CRG) were obtained after chemical reduction. The graphene content was characterized by TGA and XPS tests and the value of about 0.7 wt % was obtained. Composites of poly(lactic acid) and GF/CRG were prepared through melt blending. Thermogravimetric analysis (TGA) results shows that more than 50% graphene remains on the surface of GF after processing, which indicates a strong binding between GF and graphene. GF/CRG has significant influences on crystallization and mechanical property of PLA: the crystallinity of PLA increases from 27.61 to 51.29%; the tensile strength of the PLA–GF/CRG composite is about 63% larger than the pure PLA at the GF/CRG content of 10 wt %. This new method can apply to making composites with high performance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43296.     

Interfacial synthesis of polypyrrole/graphene composites and investigation of their optical,electrical and electrochemical properties

We report the development of a novel route for the synthesis of polypyrrole/graphene (PPy/GR) composites by liquid ? liquid interfacial polymerization, where GR and the initiator were dispersed in the aqueous phase and the monomer was dissolved in the organic phase. The synthesized samples were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, X‐ray diffraction, thermogravimetric analysis, electrochemical and electrical conductivity measurements. Structural analysis reveals a uniform dispersion of GR sheets in the PPy matrix. The composites showed noticeable improvement in thermal stability and electrical conductivity (8.45 S cm^?1) and excellent electrochemical reversibility in comparison with pure PPy. A specific capacitance of 260 F g^?1 at a current density of 100 mA g^?1 was achieved for the composite during the charge–discharge process. © 2013 Society of Chemical Industry     

Effects of treatment temperature on the reduction of GO under alkaline solution during the preparation of graphene/geopolymer composites

Homogeneously dispersed reduced-graphene-oxide (rGO) reinforced geopolymer composites were successfully prepared through in-situ reduction of graphene oxide (GO) under alkaline geopolymeric condition. The effects of treatment temperatures on the reduction of GO under the alkaline solution during the rGO/geopolymer preparation process were characterized systematically. The results showed that GO could be in situ reduced under alkaline geopolymer solution at various temperatures (25–80 °C) for 3 h. The reduction degree of rGO was improved with increasing the reaction temperature. The rGO was well dispersed, and the rGO/geopolymer composites showed amorphous structure.     

Fabrication of polypyrrole/graphene oxide nanocomposites by liquid/liquid interfacial polymerization and evaluation of their optical,electrical and electrochemical properties

A novel route has been developed to synthesize polypyrrole (PPy)/graphene oxide (GO) nanocomposites via liquid/liquid interfacial polymerization where GO and initiator was dispersed in the aquous phase and the monomer was dissolved in the organic phase. The synthesized samples were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), ultraviolet–visible absorption (UV–vis), X-ray diffraction (XRD), electrochemical and electrical conductivity measurements. A good dispersion of the GO sheets within the PPy matrix was observed from the morphological analysis. The composites exhibited noticeable improvement in thermal stability and electrical conductivity in comparison to pure polypyrrole. The composites showed excellent electrochemical reversibility at the scan rate of 0.1 V/s and good cyclic stability even up to 100th cycle. Newly developed graphene oxide based polypyrrole composite could be applied in electrochemical energy storage device.     

Synergistic effects of boron nitride sheets and reduced graphene oxide on reinforcing the thermal conduction,SERS performance and thermal property of polyimide composite films

Polyimide (PI) composite films with hybrid fillers containing hBN (hexagonal boron nitride) sheets and rGO (reduced graphene oxide) were successfully fabricated by in-situ polymerization. Herein, hBN sheets and rGO were obtained by ball milling and chemical reduction, respectively. In PI composite films, hBN can be tightly attached onto the surface of rGO via π-π interaction, which can benefit the construction of heat-conduction pathways and reduce boundary of heat resistance. The results show that the addition of rGO and hBN could enhance the thermal conductivity by synergistic effects. Specially, hBN and rGO are at the weight ratio of 1:1 and at the total loading of 33 wt%, thermal conductivity of PI composites can reach up to 1.19 Wm⁻¹ K⁻¹, which is 5.61 times higher than that of pure PI. Thermal property and dynamic mechanical property of composite films were also investigated. Besides, compared with pure PI, mixed fillers have obvious surface-enhanced Raman scattering signals, indicating the synergistic effect of the mixed fillers. Overall, this study gives insights into heat dissipative and high sensitivity analysis components which may be used in the field of high-temperature micro fabrication.