Search

Refereed/Peer-reviewed Graphene spheres confining fullerene C60 are quantitatively formed under high-shear and continuous-flow processing using a vortex fluidic device (VFD). This involves intense micromixing a colloidal suspension of graphite in DMF and an o-xylene solution of C60 at room temperature in the absence of surfactants and other auxiliary substances. The diameters of the composite spheres, C60@graphene, can be controlled with size distributions ranging from 1.5 to 3.5 μm, depending on the VFD operating parameters, including rotational speed, flow rate, relative ratio of C60 to graphite, and the concentration of fullerene. An electrode of the composite material has high cycle stability, with a high areal capacitance of 103.4 mF cm–2, maintaining its capacitances to 24.7 F g–1 and 86.4 mF cm–2 (83.5%) at a high scan rate of 100 mV s–1.

Compounds and composites with high dielectric performance are in high demand in electronic industry due to their ability to store more charge and lower energy dissipation. In this paper we present synthesis of flexible three phase nanocomposite films of graphene/titania/polydimethylsiloxane with reasonably high real part of permittivity and very low imaginary part of permittivity. Dielectric permittivity of polydimethylsiloxane was raised by addition of graphene and rutile titania used as conducting and ceramic additives, respectively added in various weight ratios. Dielectric studies of synthesized three phase graphene/titania/polydimethylsiloxane nanocomposite films with weight/weight of 2:15:20 exhibits dielectric permittivity of 34.8 even at very high frequency of 2 MHz. While loss tangent of the same three phase graphene/titania/polydimethylsiloxane nanocomposite film is as low as 0.01 and its AC conductivity is 4.3 × 10⁻⁵ Sm⁻¹. Complex impedance and complex electric modulus of three phase graphene/titania/polydimethylsiloxane nanocomposite films also confirm its capacitive behaviour. Based on these properties and results we propose that these type of three phase graphene/titania/polydimethylsiloxane nanocomposite films can be used as useful dielectric materials in energy storage devices. Refereed/Peer-reviewed

Recently, transition metal phosphates (TMPs) are demonstrated as promising candidates for supercapacitors due to their good conductivity and long-term stability. Herein, we have inrtoduced cobalt cyclotetraphosphate (Co2P4O12) as novel supercapacitive electrode material, which deliver a capacitance of 437 F/g with good stability over 3000 cycles (around 90%). To display the practical relevance, we have fabricated asymmetric device using activated carbon and Co2P4O12 as negative and positive electrodes, respecitvely, which can be operated up to 1.4 V. The introduction of redox-active moieties (such as potassium iodide (KI)) in parent KOH solution enhances the capacitance from 120 F/g to 156 F/g for Co2P4O12//AC cell with extended voltage window (1.8 V). Owing to the additional voltage and advancement in the capacitance, the cell delivers battery-level energy of 70 Wh/kg at power density of 2.3 kW/kg. It should be emphasized that even at high power (7.6 kW/kg), the cell maintained very good specific energy of 48 Wh/kg, suggesting excellent rate performance. The asymmetric device further showed long cycling stability with negligible loss and excellent Coulombic efficiency over 5000 cycles. Thus, metal cyclotetraphosphate can be employed as a promising electrode material in energy storage systems.

Composites of multi-walled carbon nanotubes (MWCNTs) and superparamagnetic magnetite nanoparticles, Fe3O4@MWCNT, were synthesized in DMF in a vortex fluidic device (VFD). This involved in situ generation of the iron oxide nanoparticles by laser ablation of bulk iron metal at 1064 nm using a pulsed laser, over the dynamic thin film in the microfluidic platform. The overall processing is a three-step in one operation: (i) slicing MWCNTs, (ii) generating the superparamagnetic nanoparticles and (iii) decorating them on the surface of the MWCNTs. The Fe3O4@MWCNT composites were characterized by transmission electron microscopy, scanning transmission electron microscope, TG analysis, X-ray diffraction and X-ray photoelectron spectroscopy. They were used as an active electrode for supercapacitor measurements, establishing high gravimetric and areal capacitances of 834 F g-1 and 1317.7 mF cm-2 at a scan rate of 10 mV s-1, respectively, which are higher values than those reported using similar materials. In addition, the designer material has a significantly higher specific energy of 115.84 W h kg-1 at a specific power of 2085 W kg-1, thereby showing promise for the material in next-generation energy storage devices. Refereed/Peer-reviewed

Graphene is extensively utilized in energy storage devices because of its high surface area and electronic conductivity as well as ease of electrode fabrication. But graphene sheets often stack themselves in polymeric matrices leading to poor capacitive performance. This problem was addressed herein by developing and inserting respectively two types of nano-sized conducting polymers into graphene interlayer spacing. The resulting hydrogel composite electrodes demonstrated efficient electron transfer for fast and reversible Faradaic reactions at the interface. Theoretical modelling by the density functional theory suggested that the reduction involve 2H + transfer steps from polyaniline to graphene oxide: the first step would be an epoxy-ring opening process after activation of the C-O bond, and the second step would be C-O rupture leading to a de-epoxidation process. This binder-free electrode demonstrated high cycling performance and ultrahigh volumetric capacitance of 612 F cm −3 , being 10 times higher than the activated carbon used in the current industry. The study represents a step forward towards the fabrication of flexible, high-energy density super capacitors. Refereed/Peer-reviewed

A new method based on scanning atmospheric plasma for an ultrafast reduction of graphene oxide (GO) and preparation of highly conductive graphene films and patterns is presented. This simple method is shown to provide a direct and scalable fabrication of graphene films on flexible and shaped substrates with a variety of patterns for broad applications. An effective and ultrafast (similar to 60 s) reduction of GO films into highly conductive graphene films at room temperature is demonstrated by this process that is impossible to achieve by conventional wet chemical and thermal reduction process. The software controlled x-y scanning unit allows fabrication of graphene films with variety of patterns on different substrates including glass, plastic, ceramics and metals with complex shapes required for flexible and wearable electronics and devices. Characterization results confirmed that a thin transparent graphene film can be produced with a surface sheets resistance of 22 k Omega/sq at the transparency of 88%, and a thick film (similar to 25 mu m) with a sheet resistance of 186 Omega/sq. A practical application of plasma fabricated graphene films was demonstrated for a supercapacitor devices able to deliver an outstanding volumetric capacitance of 536.55 F/cm(3) at a current density of 1 A/g. (C) 2017 Elsevier Ltd. All rights reserved. Refereed/Peer-reviewed

It remains a formidable challenge to develop supercapacitors having both high stretchability and electrochemical performance. A ternary polymer composite was herein developed by engineering graphene platelets (GnPs), poly (3,4-ethylenedioxythiophene) (PEDOT) and manganese dioxide (MnO2) into a kitchen sponge. Cost-effective GnPs having an electrical conductivity of 1460 S cm−1 were deposited onto the sponge pore surface by a simple dipping and drying process, followed by in situ polymerization of 3,4-ethylenedioxythiophene. MnO2 was then deposited onto the GnPs and PEDOT layers through soaking the GnP/PEDOT sponge into KMnO4 solution. When the composite was used as the electrodes for a flexible, stretchable supercapacitor, we obtained not only high specific capacitance but a high stretchability up to 400%. The supercapacitor demonstrated a specific capacitance of 802.99 F g−1 and an energy density of 55.76 Wh kg−1, with 99% capacitance retention over 1000 stretching cycles; these are attributed to the synergy between the composite components as well as the wavy device structure. The mass and thickness of the MnO2 layer was found to increase with the soak, leading to the enhancement of electrochemical performance of GnP/PEDOT/MnO2 sponge electrodes, i.e. 368.96 F g−1 for 5 min and 740.25 F g−1 for 10 min. Keywords: Graphene, Poly (3,4-ethylenedioxythiophene), Manganese oxide, Ternary composites, Stretchable supercapacitor

Flexible electronics have gained eminent importance in recent years due to their high mechanical strength and resistance to environmental conditions, along with their effective energy storage and energy generating abilities. In this work, graphene/ceramic/polymer based flexible dielectric nanocomposites have been prepared and their dielectric properties were characterized. The composite was formulated by combining graphene with rutile and anatase titania, and polyvinylidene fluoride in different weight ratios to achieve optimized dielectric properties and flexibility. After preparation, composites were characterized for their morphologies, structures, functional groups, thermal stability and dielectric characterizations by using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis and impedance spectroscopy. Dielectric results showed that prepared flexible composite exhibited dielectric constant of 70.4 with minor leakage current (tan&delta, ) i.e., 0.39 at 100 Hz. These results were further confirmed by calculating alternating current (AC) conductivity and electric modulus which ensured that prepared material is efficient dielectric material which may be employed in electronic industry for development of next generation flexible energy storage devices.

Refereed/Peer-reviewed In the present paper, synthesis and characterizations of flexible dielectric and ferroelectric polymer films combining different ratios of graphene, barium titanate and polydimethylsiloxane are presented. Broad range of characterization techniques were carried out to confirm their, morphological, structural, chemical, thermal and mechanical (flexibility, stretching, bending and twisting) characteristics. Dielectric studies showed that a high dielectric constant of the nanocomposite was dependent on the ratio of graphene:bariumtitanate:polydimethylsiloxane, showing that ratio of 15:25:100 had a high dielectric constant at high frequency range and the ratio 15:30:100 at the low frequency range. At 2 Hz the ratio 15:30:100 showed a dielectric constant of 116.9 which decreased to 30.6 at 2 MHz, thus showing capacitive nature at full frequency range. Meanwhile dielectric loss was very low i.e., 1.3 at 20 Hz and 0.02 at 2 MHz and AC conductivity was 1.6 × 10−7 S/m. Ferroelectric properties like energy density, energy loss and efficiency were calculated and compared. At an electric field of 0.92 kV/cm, remanant polarization and coercive field were 3.9 × 10−4 μC/cm2 and15.82 kV/cm, respectively. Energy density of 0.64 J/m3, energy loss 0.358 J/m3 and efficiency 64.2% were confirmed respectively. Results indicate that the nanocomposite films having desirable performances such as flexibility, thermal stability, high dielectric constant, high energy density are good candidates to be considered in energy storage and memory device applications.

Electrically conductive and robust composite hydrogel films are the increasing demand for compact and portable energy storage systems and biosensor. We herein present a simple route for electrically conductive and strong graphene/poly(vinyl alcohol) (PVA) composite hydrogel films by a casting method using processable graphene sheets. Both pure PVA and graphene/PVA composite hydrogel films were characterized by various techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), electrical, and mechanical measurements. High-quality, processable graphene sheets effectively enhanced the composite's electrical conductivity; a percolation threshold was achieved at 4.6 vol% of graphene mass loading. At 10 wt% nanomaterials loading, Young's modulus, and tensile strength improved by 369% and 930%, respectively, compared with neat PVA hydrogel films. The significant reinforcement found in composite films containing water attributed to strong interface between water, high-quality graphene sheets, and PVA polymer chains. As supercapacitor electrodes, composite hydrogel film delivered a gravimetric capacitance of 9.5 F/g. This work provides a new approach for fabricating electrically conductive hydrogel films using nonconducting polymer for supercapacitor Refereed/Peer-reviewed

This paper presents a new and facile method to prepare molybdenum disulfide (MoS2)/graphene composites and their inks based on an improved ball milling process. The developed method is cost effective, environmentally friendly, and scalable, producing few-layer MoS2 material and MoS2/graphene-based inks. The prepared inks after characterization by SEM, Raman, XRD, FTIR, CA and rheology were used to fabricate electrodes for supercapacitors by adopting two designs: 2D printed and sandwiched electrodes. The electrodes showed excellent electrochemical performance with a specific capacitance of 392 Fg−1 at 5 mV s−1 and low equivalent resistance of 0.41 Ω, which outperforms the properties of graphene electrodes. The specific capacitance of electrodes prepared by 2D printing using MoS2/graphene ink was 76 Fg−1 at 5 mV s−1 with an areal capacitance of 58.5 mF/cm−2 at 0.77 mg/cm−2, demonstrating high energy storage capability. The performance of the MoS2/graphene composites and their inks highlights their promising application as electrode materials for high-performance energy storage devices.

Potassium (K) ion storage technology is recently receiving a great attention due to their low-cost and enormous abundance on the earth compared to lithium. However, the technology is still at a scientific research stage and exploring suitable electrode materials is a key challenge. Herein, we have engineered nitrogen doped carbon nanotubes (N-CNTs) as a promising anode material for K-ion storage through pyrolytic decomposition of polyaniline nanotubes (PAni-NTs). These N-CNTs delivers high reversible capacity with good rate performance and cycling stability. Taking advantage of these features, a potassium-ion hybrid capacitor (KIHC) is constructed using N-CNTs as battery-type anode and 3-dimensional (3D) laser scribed graphene (LSG) as capacitor-type cathode electrodes. The device displays a high energy density of 65 W h/kg, a high power output of 1000 W/kg, as well as a long cycling life (91% capacity retention over 5000 cycles). Thus, such an advanced energy storage system can satisfy the requirements of high power and high energy densities simultaneously in diverse applications at low-cost Refereed/Peer-reviewed

Supercapacitors (SCs) due to their high energy density, fast charge storage and energy transfer, long charge discharge curves and low costs are very attractive for designing new generation of energy storage devices. In this work we present a simple and scalable synthetic approach to engineer ternary composite as electrode material based on combination of graphene with doped metal oxides (iron oxide) and conductive polymer (polypyrrole) with aims to achieve supercapacitors with very high gravimetric and areal capacitances. In the first step a binary composite with graphene mixed with doped iron oxide (rGO/MeFe2O4) (Me = Mn, Ni) was synthesized using new single step process with NaOH acting as a coprecipitation and GO reducing agent. This rGO/MnFe2O4 composite electrode showed gravimetric capacitance of 147 Fg−1 and areal capacitance of 232 mFcm−2 at scan rate of 5 mVs−1. In the final step a conductive polypyrrole was included to prepare a ternary composite graphene/metal doped iron oxide/polypyrrole (rGO/MnFe2O4/Ppy) electrode. Ternary composite electrode showed significantly improved gravimetric capacitance and areal capacitance of 232 Fg−1 and 395 mFcm−2 respectively indicating synergistic impact of Ppy additives. The method is promising to fabricate advanced electrode materials for high performing supercapacitors combining graphene, doped iron oxide and conductive polymers.

To address the limitations of piezoelectric polymers which have a low dielectric constant andto improve their dielectric and ferroelectric efficiency for energy storage applications, we designed and characterized a new hybrid composite that contains polyvinylidene fluoride as a dielectric polymer matrix combined with graphene platelets as a conductive and barium titanite as ceramic ferroelectric fillers. Different graphene/barium titanate/polyvinylidene fluoride nanocomposite films were synthesized by changing the concentration of graphene and barium titanate to explore the impact of each component and their potential synergetic effect on dielectric and ferroelectric properties of the composite. Results showed that with an increase in the barium titanate fraction, dielectric efficiency ofthe nanocomposite was improved. Among all synthesized nanocomposite films, graphene/barium titanate/polyvinylidene fluoride nanocomposite in the weight ratio of 0.15:0.5:1 exhibited thehighest dielectric constant of 199 at 40 Hz, i.e., 15 fold greater than that of neat polyvinylidene fluoride film at the same frequency, and possessed a low loss tangent of 0.6. However, AC conductivity and ferroelectric properties of graphene/barium titanate/polyvinylidene fluoride nanocomposite films were enhanced with an increase in the graphene weight fraction. Graphene/barium titanate/polyvinylidene fluoride nanocomposite films with a weight ratio of 0.2:0.1:1 possessed a high AC conductivity of 1.2 &times, 10&minus, 4 S/m at 40 Hz. While remanent polarization, coercive field, and loop area of the same sample were 0.9 &mu, C/cm2, 9.78 kV/cm, and 24.5 &mu, C/cm2&middot, V, respectively. Our results showed that a combination of graphene and ferroelectric ceramic additives are an excellent approach to significantly advance the performance of dielectric and ferroelectric properties of piezoelectric polymers for broad applications including energy storage.

A novel porous 3D-structured carbon composite material with a unique architecture by combining graphene and carbonized metal-organic framework (C-MOF) (HKUST-1) microrods for high performing supercapacitors has been synthesised and characterised. The HKUST-1 microrods were prepared by a new method, converting their diamond-like shape into microrods via mechanical shear mixing in an aqueous solution. Grinding of HKUST-1 and graphene oxide (GO) resulted in the formation of a 3D GO-MOF composite with intercalated HKUST-1 microrods between GO sheets. The composite film was treated by a laser scribing method and created a highly porous, a high surface area (>600 m²/g) and conductive 3D nanostructured composite film (L-rGO-C-MOF) used as electrodes for supercapacitor applications. The prepared film showed a high capacitance of 390 F/g at 5 mV/s, and a cyclic stability of 97.8% at 10 A/g after 5000 cycles. The symmetrical supercapacitor delivered an excellent power density of 8037.5 W/kg with an outstanding energy density of 22.3 Wh/kg confirming a new pathway to design new 3D porous graphene-MOF composites for high-performance energy storage devices. Refereed/Peer-reviewed

Layered double hydroxide (LDH) nanoparticles have tremendous anion-intercalating property. Co–Fe LDH has been synthesized using the ball milling method. Characterization of Co–Fe LDH was done by XRD, SEM, TEM and FT-IR. The prepared LDH was used, for the first time, as a catalyst for multi-walled carbon nanotubes (MWCNTs) via chemical vapor deposition (CVD) of acetylene at different temperatures (400–700 °C). Also, the ability of Co–Fe LDH as an adsorbent was investigated for the removal of Cd2+ ions from aqueous solutions. Various physicoechemical parameters such as pH, initial metal ion concentration, and time were studied. To get the adsorption isotherms, the concentrations of the metal ions ranging from 6 to 18 mg/l were used. The adsorption process follows pseudo-second-order reaction kinetics, as well as Langmuir adsorption isotherms. Interestingly, Co–Fe LDH demonstrated 95% Cd2+ removal at pH 9 and 6 h which could be applied in wastewater treatment characterized by a high efficiency and low cost. Refereed/Peer-reviewed

Background: The nature of graphene makes it a highly sought after material for transparent and non transparent electrodes and double electrode designs for supercapacitors. It has been well documented that graphene can be used for transparent electrodes in flat panel displays, tough screens, and solar cells. In this case of supercapacitors, transparency is less important than energy storage capacity. However, even in this application, graphene has the potential to excel. A significant number of very recent inventions disclose the use of graphene as various electrodes for such applications and are compiled in this review article. Objective: This review article covers the existing knowledge and patent base for manufacturing of graphene as well as the very recent patent base for the use of graphene as transparent electrode for application such as display devices and touch screen and the manufacturing of such devices and graphene based components. Method: The US Patent Base was thoroughly searched in order to review the existing patents on graphene based transparent electrodes for flat panel display devices as well as supercapacitors and their fabrication. Results: A large number of patents disclose the application and fabrication of graphene based flat panel display devices and supercapacitors and their fabrication. In some cases, graphene is not specifically mentioned, but carbon containing materials which include graphene. Just the very recent existing patent base disclosed a wide range of applications based on graphene including flat panel display devices, touch panel devices, and supercapacitors. The article covers more than 40 patents from the period between 2015 and 2017. Conclusion: The significant number of literature and patents, which discloses numerous methods to prepare graphene, fabricate and apply components based on graphene, and manufacture devices based on such components, makes it evident that graphene is considered to be an important material for the next generation of transparent and non transparent electrodes and supercapacitors. Refereed/Peer-reviewed

Combined convection and radiation in simultaneously developing laminar flow and heat transfer is numerically considered with a discrete-direction method. Coupled heat transfer in absorbing emitting but not scattering gases is presented in some cases of practical situations such as combustion of natural gas, propane and heavy fuel. Numerical calculations are performed to evaluate the thermal radiation effects on heat transfer through combustion products flowing inside circular ducts. The radiative properties of the flowing gases are modeled by using the absorption distribution function (ADF) model. The fluid is a mixture of carbon dioxide, water vapor, and nitrogen. The flow and energy balance equations are solved simultaneously with temperature dependent fluid properties. The bulk mean temperature variations and Nusselt numbers are shown for a uniform inlet temperature. Total, radiative and convective mean Nusselt numbers and their axial evolution for different gas mixtures produced by combustion with oxygen are explored.

Polyaniline (PANi)/graphene nanocomposites have attracted tremendous interest because of their great potential in electrochemical energy storage applications, especially supercapacitors. We herein focus on the composite synthesis, device fabrication and particularly various techniques for the improvement of electrochemical performance. It is imperative to take close control of the interface in these nanostructured composites, which thus would lead to the desired synergistic effects and cyclic stability with the efficient diffusion of electrolyte ions and electrons. Challenges and perspectives are discussed for the development of highly efficient PANi/graphene electrodes for supercapacitors. Refereed/Peer-reviewed

Three types of compressible, electrically conductive aerogels have been developed in this study usingpoly(3,4-ethylenedioxythiophene) - polystyrene sulfonate (PEDOT-PSS). The crosslinking between PEDOT-PSS and polyethylene oxide (PEO) promoted the formation of welded fibre-like morphology, which was explained through the purpose-designed experiment and characterization. Single-walled carbon nanotubes (SWCNTs) were added to further improve the electrical conductivity and thus the electrochemical performance. The PEDOT-PSS/PEO/SWCNT aerogel was used to fabricate a flexible supercapacitor which exhibited a specific capacitance of 362 F g1 at a scan rate of 20 mV s1; it demonstrated an energy density of 67.7 Wh kg1 and a power density of 13.5 kW kg1 at 100 mV s1 with 0e1.8 V potential window. When bent at 60, the supercapacitor exhibited 318 F g1 at 100 mV s1.The flexible supercapacitor showed a 94.6% retention after 5000 cycles at 5 A g1. Refereed/Peer-reviewed

High volumetric capacitance is vital for the development of wearable and portable energy storage devices. We herein introduce a novel simple route for the fabrication of a highly porous, binder-free and free-standing polyaniline/reduced graphene oxide composite hydrogel (PANi/graphene hydrogel) as an electrode with a packing density of 1.02 g cm−3. PANi played critical roles in gelation, which include reduction, crosslinking, creation of pseudocapacitance and as a spacer preventing graphene sheets from stacking. The composite hydrogel film delivered a volumetric capacitance of 225.42 F cm−3 with a two-electrode supercapacitor configuration, which was enhanced to 592.96 F cm−3 in a redox-active electrolyte containing hydroquinone. This new strategy will open a new area for using conducting polymer derivatives in the development of flexible graphene electrodes towards many applications such as batteries, sensors and catalysis. Refereed/Peer-reviewed

We in this study used a commercial grade kitchen sponge as the scaffold where both graphene platelets (GnPs) and polyaniline (PANi) nanorods were deposited. The high electrical conductivity of GnPs (1460 S cm-1) enhances the pseudo-capacitive performance of PANi grown vertically on the GnPs basal planes; the interconnected pores of the sponge provide sufficient inner surface between the GnPs/PANi composite and the electrolyte, which thus facilitates ion diffusion during charge and discharge processes. When the composite electrode was used to build a supercapacitor with two-electrode configuration, it exhibited a specific capacitance of 965.3 F g-1 at a scan rate of 10 mV s-1 in 1.0 M H2SO4 solution. In addition, the composite Nyquist plot showed no semicircle at high frequency corresponding to a low equivalent series resistance of 0.35 Ω. At 100 mV s-1, the supercapacitor demonstrated an energy density of 34.5 Wh kg-1 and a power density of 12.4 kW kg-1 based on the total mass of the active materials on both electrodes. To demonstrate the performance, we built an array consisting of three cells connected in series, which lit up a red light emitting diode for five minutes. This simple method holds promise for high-performance yet low-cost electrodes for supercapacitors. Refereed/Peer-reviewed