Supercapacitor device performances of polycarbazole/graphene and polycarbazole/nanoclay/graphene nanocomposites

In this study, graphene oxide (GO) is chemically reacted with sodium borohydride (NaBH₄) to form reduced graphene oxide (rGO). rGO, polycarbazole (PCz)/rGO and PCz/nanoclay/rGO materials were obtained by chemical polymerisation method. These three materials were characterised by Fourier-transform infra-red spectroscopy-attenuated transmission reflectance, scanning electron microscopy, energy-dispersive X-ray analysis, cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy. The PCz/nanoclay/rGO nanocomposite shows significantly improved capacitance (C_sp?=?187.78?F?g^?1) compared to that of PCz/rGO (C_sp?=?74.18?F?g^?1) and rGO (C_sp?=?20.78?F?g^?1) at the scan rate of 10?mV?s^?1 by CV method. The supercapacitor device performance results show high power density (P?=?1057.81?W?kg^?1) and energy density (E?=?1.7?Wh?kg^?1) obtained from Ragone plot for PCz/nanoclay/rGO material. Stability tests were also examined by the CV method for 1000 cycles.     

One-step electrosynthesis of MnO2/rGO nanocomposite and its enhanced electrochemical performance

We present a facile one-step electrochemical approach to generate MnO₂/rGO nanocomposite from a mixture of Mn₃O₄ and graphene oxide (GO). The electrochemical conversion of Mn₃O₄ into MnO₂ through potential cycling is expedited in the presence of GO while the GO is reduced into reduced graphene oxide (rGO). The MnO₂ nanoparticles are evenly distributed on the rGO nanosheets and act as the spacer to prevent rGO nanosheets from restacking. This unique structure provides high electroactive surface area (1173?m² g^?1) that improves ions diffusion within the MnO₂/rGO structure. As a result, the MnO₂/rGO nanocomposite exhibits high specific capacitance of 473?F?g^?1 at 0.25?A?g^?1, which is remarkably higher (3 times) than the Mn₃O₄/GO prior conversion. In addition, the electrosynthesized nanocomposite shows higher conductivity and excellent potential cycling stability of 95% at 2000 cycles.     

Preparation of manganese monoxide@reduced graphene oxide nanocomposites with superior electrochemical performances for lithium-ion batteries

Manganese monoxide (MnO) nanowire@reduced graphene oxide (rGO) nanocomposites are synthesized using a simple hydrothermal method combined with a calcination process. The structural and morphological characterization of the composites indicates that the MnO nanowires homogeneously anchor on both sides of the cross-linked rGO. The nanocomposites exhibit a high surface area of 126.5?m² g^?1. When employed as an anode material for lithium-ion batteries, the nanocomposites exhibit a reversible capacity of 1195 mAh g^?1 at a current density of 0.1?A?g^?1, with a high charge-discharge efficiency of 99.2% after 150 cycles. The three-dimensional architecture of the present materials exhibits high porosity and electron conductivity, significantly shortening the diffusion path of lithium ions and accelerating their reaction with the electrolyte, which greatly improves the lithium-ion storage properties. These excellent electrochemical performances make the composite a promising electrode material for lithium-ion batteries.     

Electrochemical behavior of CuO/rGO nanopellets for flexible supercapacitor,non-enzymatic glucose,and H2O2 sensing application

In the present article, graphene oxide (GO) sheets and monoclinic copper oxide (CuO) nanocrystals are connected with each other and result in the formation of CuO/rGO nanopellets, and these nanopellets synthesized using coprecipitation method. The nanopellet structured CuO/rGO composite on carbon cloth, which act as current collector exhibits specific capacitance of 188 F g^?1 at a current density of 0.2 A g^?1 and up to 96.3% capacity retention after 2000 charge-discharge cycles. It shows a maximum energy density of 7.32 Wh kg^?1 and power density of 53 W kg^?1. The glucose sensing characteristics of CuO/rGO nanopellet is investigated on carbon cloth and ITO substrate. It shows glucose sensitivity of 0.805 mA mM^?1 cm^?2 and 0.2982 mA mM^?1 cm^?2 for a bundle like structured CuO/rGO composite on carbon cloth and ITO substrate, respectively. Further H₂O₂ sensing is studied on ITO substrate, which manifests H₂O₂ sensitivity of 84.39 μA mM^?1 cm^?2. The results indicate that nanopellet structured CuO/rGO composite could be a promising electrode material for supercapacitor, glucose, and H₂O₂ sensor.     

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.     

Al-doping driven electronic structure of α-NiS hollow spheres modified by rGO as high-rate electrode for quasi-solid-state capacitor

Developing an optimized electronic structure of α-NiS electrode material is critical for its high-rate electrochemical performance of quasi-solid-state capacitor. Herein, Al³⁺ have been doped into α-NiS lattice and the reduced graphene oxide (rGO) is employed to modify Al-doping α-NiS, to alleviate the low-mobility charge of α-NiS. The electronic structure and electrochemical properties of α-NiS hollow spheres induced by Al-doping and rGO modification are investigated, both experimental characterization and theoretical results confirm Al-doping affect the electronic structure and electrochemical performance of α-NiS hollow spheres. In the composite of Al-doping α-NiS and rGO (named as Al_xNi_1-xS/rGO), the doped heteroatom improves the intrinsic electronic structure of α-NiS and the rGO provides a good electric conducting network, leading to an enhanced electrochemical performance of α-NiS as high-rate electrode material. After evaluation, the optimized Al_0.2Ni_0.8S/rGO composite shows a superior reversible capacity of 1096 C g^?1 at 2 A g^?1, and retains a capability of 471 C g^?1 at a high-rate of 30 A g^?1. Moreover, an asymmetric quasi-solid-state hybrid capacitors assembled by Al_0.2Ni_0.8S/rGO and activated carbon presents a high energy density of 30.6 Wh kg^?1. This work provides a foundational strategy for the modification of α-NiS through Al-doping and combining with rGO, which has a positive effect on α-NiS electrode material in quasi-solid-state hybrid capacitors.     

Li0.95Na0.05MnPO4/C nanoparticles compounded with reduced graphene oxide sheets for superior lithium ion battery cathode performance

Sodium-substituted LiMnPO₄/C/reduced graphene oxide (LNMP@rGO) was synthesized in this study via freeze drying and carbon thermal reduction method with graphene oxide as carbon source. Sodium ion doping is optimized and rGO effects are evaluated by XRD, SEM, TEM, BET, Raman, and electrochemical performance measurements. Well-distributed nanoparticles with average size of ~50?nm are evenly distributed on the surface or intercalation between rGO layers, resulting in a porous ion/electronic conductive network. Compared to 122.3?mA?h?g^?1 in unmodified LNMP, the best LNMP@rGO (20?mg rGO) exhibits an excellent initial discharge capacity of 150.4?mA?h?g^?1 at 0.05?C at 122.9% of the initial capacity. The capacity retention rate is 95.8% of the initial capacity after 100 cycles at 1?C. Capacity of 101.2?mA?h?g^?1 is preserved even at rates as high as 10?C.     

V2O3/rGO composite as a potential anode material for lithium ion batteries

V₂O₃ is a promising anode material and has attracted the interests of researchers because of its high theoretical capacity of 1070?mAh?g^?1, low discharge potential, inexpensiveness, abundant sources, and environmental friendliness. However, the development and application of V₂O₃ have been hindered by the low conductivity and drastic volume change of V₂O₃ composites. In this work, V₂O₃/reduced graphene oxide (rGO) nanocomposites are successfully prepared through a facile solvothermal method and annealing process. In this synthesis protocol, V₂O₃ nanoparticles (NPs) are encapsulated by rGO. This unique structure enables rGO to inhibit volume changes and improve the ion and electronic conductivity of V₂O₃. In addition, V₂O₃ NPs, which exhibit sizes of 5–40?nm, are uniformly dispersed on rGO sheets without aggregation. The Li⁺ storage behavior of V₂O₃/rGO is systematically investigated in the potential range 0.01–3.0?V. The V₂O₃/rGO nanocomposite can achieve a high reversible specific capacity of 823.4?mAh?g^?1 under the current density of 0.1?A?g^?1, and 407.3 mAh g^?1 under the high current density of 4.0?A?g^?1. The results of this study provide insight into the fabrication of rGO-based functional materials with extensive applications.     

Vertically aligned,polypyrrole encapsulated MoS2/graphene composites for high-rate LIBs anode

Ultrathin MoS₂ nanosheets were vertically anchored on the reduced graphene oxide (MoS₂/rGO) via hydrothermal method. To further engineering the surface conductivity, ultrathin polypyrrol (PPy) layer was coated on the MoS₂/rGO composite via in situ polymerization to form a bi-continuous conductive network with a sandwich-like structure. The graphene nanosheets and the PPy coating can facilitate the electrons transfer rate, while the ultrathin MoS₂ nanosheets can enhance the utilization efficiency of the active materials. The obtained MoS₂/rGO-10 composite exhibits high reversible specific capacity (970?mAh?g^?1 at 0.1?A?g^?1) and rate capability (capacity retention of 64% at 3.2?A?g^?1). Moreover, the PPy@MoS₂/rGO hybrids reveal lower specific capacity but better rate capability, and a “trade-off” effect between electrons and ions transfer resistance was observed. This easy-scalable PPy surface conductivity engineering strategy may be applied in the preparation of high-performance LIBs active materials.     

Hexagonal boron nitride nanosheet/carbon nanocomposite as a high-performance cathode material towards aqueous asymmetric supercapacitors

The two-dimensional hexagonal boron nitride (h-BN) has garnered tremendous interest due to its unique mechanical, thermal and electronic properties. However, the application of h-BN has been restricted as electrode materials for supercapacitors because of its wide band gap and rather low conductivity. Herein, a carbon-modified hexagonal boron nitride nanosheet (h-BN/C) nanocomposite is prepared through a facile and scalable solid-state reaction. Interestingly, the h-BN/C nanocomposite as cathode material exhibits a pair of distinct and reversible redox peaks in 2?M KOH aqueous electrolyte. Because of the enhanced electrical conductivity derived from the modified carbon and the increased specific surface area, the h-BN/C nanocomposite presents a high specific capacitance of 250?F?g^?1 at the current density of 0.5?A?g^?1. More importantly, the fabricated aqueous asymmetric supercapacitor with the h-BN/C as cathode and activated carbon as anode displays an operating voltage of 1.45?V, an energy density of 17?Wh?kg^?1 at a power density of 245?W?kg^?1, and high stability up to 1000 cycles. Therefore, h-BN/C nanocomposite would promisingly be a cathode material for aqueous asymmetric supercapacitors.     

Simultaneous reduction and surface functionalization of graphene oxide for enhancing flame retardancy and thermal conductivity of mesogenic epoxy composites

Graphene oxide (GO ) is reduced and surface functionalized by 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide simultaneously. This functional reduced graphene oxide (F‐rGO ) with better thermal stability can be used as a nano‐filler to improve the flame retardancy, mechanical properties and thermal conductivity of mesogenic epoxy (EO ). Due to the presence of an oriented structure, EO is an intrinsic highly thermal conductive polymer compared with common polymer. After being filled with F‐rGO , the ordered domains in the EO matrix are connected by F‐rGO . As a result, the thermal conductivity coefficient of F‐rGO /EO composite is increased by 30.8% compared with pure EO . The dynamic mechanical analysis results indicate that E ' of F‐rGO /EO is 26.7% higher than that of EO . Because of the stable structure of F‐rGO , F‐rGO /EO is self‐extinguishing. The total heat release of F‐rGO /EO ‐15 is 24.1 kJ g^?1, which is 5.6 kJ g^?1 lower than that of EO . © 2016 Society of Chemical Industry     

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     

Robust and conductive mesoporous reduced graphene oxide-silica hybrids achieved by printing and the sol gel route

Reduced graphene oxide (rGO) scaffoldings are used as templates to create lightweight 3D rGO/silica and rGO/silico-aluminate hybrids by a simple impregnation route and the sol-gel method. The printed rGO assemblies are infiltrated by the corresponding alkoxide precursor solution and gelled by exposure to ammonia vapours, producing an hybrid replica of the rGO structure. The hybrids show a significant prevalence of mesopores, with total porosity above 94 %, density of ～ 0.1 g?cm^?3 and high specific surface area (≥ 190 m²?g^?1). As a result, the 3D composite materials show enhanced water adsorption capacity and hydrophilicity, display compressive strengths in the range 0.1 – 0.4 MPa, which scale with the proportion of silica (or Al-modified silica) on the hybrid scaffold, and electrical conductivities are above 60 S?m^?1. These properties are very attractive for applications in the removal of pollutants, water filtering, catalysis, drug delivery, or energy production and storage.     

Wrapping mesoporous Fe2O3 nanoparticles by reduced graphene oxide: Enhancement of cycling stability and capacity of lithium ion batteries by mesoscopic engineering

The fast capacity fading at high current density turns out to be one of the key challenges limiting the broad applications of transition metal oxide-based electrodes. Herein, Fe₂O₃ nanoparticles with well-defined mesopores wrapped by reduced graphene oxide (RGO) have been synthesized via a facile hydrothermal strategy. The as-prepared nanocomposites were systematically characterized. XPS and Raman analyses confirm the co-existence of Fe₂O₃ and RGO in the nanocomposite system. SEM and TEM reveal that the mesoporous Fe₂O₃ nanoparticles have a size of 20–60?nm and are uniformly dispersed and tightly wrapped by RGO. When used as the anode in lithium ion batteries, the mesoporous-Fe₂O₃/RGO electrode exhibits excellent cycling stability (1098?mA?h?g^?1 after 500 cycles at 1?A?g^?1) and superior rate capability (574?mA?h?g^?1 at 5?A?g^?1). The excellent electrochemical performance can be mainly ascribed to the unique mesoscopic architecture that serves as a cushion to alleviate volume change of Fe₂O₃ during discharge/charge cycles, provides a sustainably large contact area with the electrolyte, and improves electrical conductivity. This unique nanocomposite electrode holds great potential as an anode material for advanced lithium ion batteries.     

In situ co-deposition of nickel hexacyanoferrate nanocubes on the reduced graphene oxides for supercapacitors

A facile co-precipitation strategy is developed to prepare nickel hexacyanoferrate nanocubes (NiHCF NBs) supported on the reduced graphene oxide (rGO) in the presence of poly(diallyldimethylammonium chloride) (PDDA). The NiHCF NBs are uniformly deposited on the rGO by electrostatic interaction. Their size can be tuned from 10 nm to 85 nm by changing their content from 32.6% to 68.2%. Under the optimal condition, NiHCF/PDDA/rGO hybrids are composed of 51.4% NiHCF NBs with an average size of 38 nm. The specific capacitance of NiHCF/PDDA/rGO hybrids reaches up to 1320 F g⁻¹ at a discharge density of 0.2 A g⁻¹, more than twice that of the pure NiHCF, as well as slight capacitance decay by 15% at 0.2 A g⁻¹ and excellent cycling stability with 87.2% of its initial capacitance after 10,000 discharge/charge cycles. More importantly, NiHCF/PDDA/rGO hybrids exhibit an ultrahigh energy density of 58.7 Wh kg⁻¹ at the power density of 80 W kg⁻¹. The superior storage energy performance of NiHCF/PDDA/rGO hybrids, such as high specific capacitance, good rate capacity and long cycling stability, positions them as a promising candidate for supercapacitor materials.     

Synthesis of reduced graphene oxide/tungsten trioxide nanocomposite electrode for high electrochemical performance

A facile and well-controllable reduced graphene oxide/tungsten trioxide (rGO/WO₃) nanocomposite electrode was successfully synthesized via an electrostatic assembly route at 350 rpm for 24 h. In this study, hexagonal-phase WO₃ (h-WO₃) nanofiber was well distributed on rGO sheets by applying optimal processing parameters. The as-synthesized rGO/WO₃ nanocomposite electrode was compared with pure h-WO₃ electrode. A maximum specific capacitance of 85.7 F g⁻¹ at a current density of 0.7 A g⁻¹ was obtained for the rGO/WO₃ nanocomposite electrode, which showed better electrochemical performance than the WO₃ electrode. The incorporation of WO₃ into rGO could prevent the restacking of rGO and provide favourable surface adsorption sites for intercalation/de-intercalation reactions. The impedance studies demonstrated that the rGO/WO₃ nanocomposite electrode exhibited lower resistance because of the superior conductivity of rGO that improved ion diffusion into the electrode. To evaluate the contribution of WO₃ to the rGO/WO₃ nanocomposite, the influence of mass loading of WO₃ on the capacitance was investigated.     

Three-dimensional graphene layers prepared by a gas-foaming method for supercapacitor applications

Inspired by baking bread, our research group demonstrates a novel method for baking three-dimensional (3D) graphene layers with an open porous network, pore size in the range of dozens of nanometers to several hundred nanometers, and a pore wall thickness of about 10 nm. Such continuously cross-linking structures not only effectively overcome the restacking and agglomeration of graphene nanosheets but also possess more channels between nanosheets to lower the resistance for electron access to the inter-space. Compared with reduced graphene oxide (rGO) prepared at the same temperature, the unique 3D porous-structured graphene layers also contain 4.3 at.% nitrogen. When the 3D graphene layers are employed as an active electrode material for a supercapacitor, a high specific capacitance (SC) of 231.2 F g⁻¹ at 1 A g⁻¹ is displayed after electrochemical activation, approximately two times that of rGO. Only <1.0% of the capacitance degrades after 8000 cycles, exhibiting its excellent cycle stability; furthermore, it liberates a high energy density of 32.1 Wh kg⁻¹ at a power density of 500 W kg⁻¹. The attractive performances of 3D graphene layers make them a promising candidate as an electrode material for supercapacitors.     

Multiwalled carbon nanotubes/polypyrrole/graphene/nonwoven fabric composites used as electrodes of electrochemical capacitor

The reduced graphene oxide/nonwoven fabric (rGO/NWF) composites have been fabricated through heating the NWF coated with the mixture of GO and HONH₂·HCl at 130°C, during which the GO is chemically reduced to rGO. Then the composites of polypyrrole (PPy)/rGO/NWF have been prepared through chemically polymerizing pyrrole vapor by using the FeCl₃·6H₂O adsorbed on rGO/NWF substrate as oxidant. Finally, multiwalled carbon nanotubes (MWCNTs) are used as conductive enhancer to modify PPy/rGO/NWF through dip‐dry process to obtain MWCNTs/PPy/rGO/NWF. The prepared composites have been characterized and their capacitive properties have been evaluated in 1.0M KCl electrolyte by using two‐electrode symmetric capacitor test. The results reveal that MWCNTs/PPy/rGO/NWF possesses a maximum specific capacitance (C_sc) of about 319 F g^?1 while PPy/rGO/NWF has a C_sc of about 277.8 F g^?1 at the scan rate of 1 mV s^?1 and that optimum MWCNTs/PPy/rGO/NWF retains 94.5% of initial C_sc after 1000 cycles at scan rate of 80 mV s^?1 which is higher than PPy/rGO/NWF (83.4%). Further analysis reveals that the addition of MWCNTs can increase the charger accumulation at the outer and inner of the composites, which is favorable to improve the stability and the rapid charge‐discharge capacity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41023.     

Facile preparation of Ni-doped MnCO3 materials with controlled morphology for high-performance supercapacitor electrodes

Doping homogeneous elements and conducting morphological adjustment as commonly-used modification methods are both effective to promote the electrochemical properties of electrode materials. In this work, nickel-doped manganese carbonate with 3D flower-like structure was synthesized by a one-step hydrothermal method, and the corresponding growth mechanism was investigated. The electrochemical characteristics of as-fabricated electrode materials were measured, among which 3D self-assembled Ni_0.2Mn_0.8CO₃ nanoflower with large surface area exhibited superior areal capacitance of 583.5?F?g^?1 at 1?A?g^?1 (fourfold more than MnCO₃ microcubes), excellent electrical conductivity as well as satisfactory cycling stability (84.78% capacitance retention after 2000 cycles at 2?A?g^?1). In addition, the asymmetric supercapacitor assembled with Ni_0.2Mn_0.8CO₃ as cathode and commercial activated carbon as anode displayed a high energy density of 24.1?Wh?kg^?1 at the power density of 0.74?kW?kg^?1 and showed a desirable cycle life. In summary, the unique 3D flower-like Ni_0.2Mn_0.8CO₃ nanomaterial could be regarded as a promising electrode material for high-performance supercapacitors.     

A new As3Mo8V4/PANi/rGO composite for high performance supercapacitor electrode

Herein, [As₂^IIIAs^VMo₈^VIV₄^IVO₄₀]₂[Cu^ICu₂^II(pz)₄]₂·9H₂O/polyaniline/reduced graphene oxide (pz = pyrazine, abbreviated to As₃Mo₈V₄/PANi/rGO) composite is first assembled, characterized and systematically explored for its supercapacitor performance. As₃Mo₈V₄/PANi/rGO composite shows a exceptional specific capacitance (2351 F g^?1 at 1 A g^?1) and outstanding cyclic stability (96.9% after 5000 cycles). The symmetric supercapacitor exhibits high specific capacitance of 1295 F g^?1 at 1 A g^?1 and excellent energy density of 88.1 Wh kg^-1 at power density of 349.6 W kg^-1, while maintaining a notable capacitance retention of 85.7% after 5000 cycles at 2 A g^-1. The above results confirm the potential application of As₃Mo₈V₄/PANi/rGO composite in energy storage devices.