Flexible Graphite Sheet Research Articles

Enhancing the electrochemical performance of graphite sheet electrodes for ketamine detection

Flexible graphite sheets (GS) have been a promising material for developing electrochemical sensors. In this work, we showed that the electrochemical activation protocol (+1.4 V followed by -1.0 V vs. Ag|AgCl|KCl(sat.) both at 200 s) in alkaline medium (0.5 mol l-1 NaOH) enhances the electrochemical activity of GS. Before the treatment, cyclic voltammetric profile of inner-sphere [Fe(CN)6]3-/4- redox couple at 50 mV s-1 exhibited an ill-defined voltammetric profile (ΔEp = 800 mV) while an increase in the reversibility was achieved (ΔEp = 225 mV) after the treatment. Additionally, the lower charge transfer resistance (Rct) measured by Electrochemical Impedance Spectroscopy (EIS) and a higher heterogeneous electron transfer constant (k0) corroborate with the enhancement in the electrochemical performance of treated GS electrodes. The SEM images revealed an irregular pattern with number of grooves, indicating a partially surface exfoliation and AFM analysis displayed an increase in the roughness. These findings agreed with the estimation of electroactive area which increased 3-times after the treatment. As proof of concept, ketamine (KET), an anesthetic often used as drug of abuse, was determined in synthetic saliva and veterinary pharmaceutical samples using treated GS electrodes and square wave voltammetric measurements. Linear range of 5.0–100.0 µmol l-1 with a limit of detection value of 2.1 µmol l-1 was obtained for KET. Appropriate recovery values (∼105 %) for the analysis of samples were achieved.

Evaluating the role of current collectors in supercapacitor electrodes with NiCo2O4 nanospheres

Supercapacitor as an electrochemical energy storage device is well known for delivering high power density than batteries but faces the challenge of lower electrical energy density. To overcome this limitation, researchers are exploring new and advanced nanostructured electrode materials, particularly metal oxides, and composites. Most of the supercapacitor research is focused on investigating electrode materials, which are important in determining the device's electrochemical performance. Along with this premise, this study says that a current collector (CC) plays an essential part in an electrode's electrochemical performance and is just as important as the electrode material. It is crucial to investigate the role of current collectors in supercapacitor electrode electrochemical performance. In this study, four different current collectors are used to deposit NiCo2O4 (NCO) as the active electrode material: nickel foam (Ni), flexible graphite sheet (FG), copper foil (Cu), and stainless-steel foil (SS). The electrochemical tests are performed with and without active material loaded on different CCs and investigated for the contribution made by each CC. Results indicate that Ni foam possesses its own specific capacity of 128 Fg-1 and as an electrode, NCO–Ni delivered the highest specific capacity of 960 Fg-1 at a current density of 1 Ag-1, compared with NCO-FG (237 Fg−1), NCO–Cu (169 Fg−1), and NCO-SS (64 Fg−1) electrodes.

Long-Term Performance of Semimetallic Gaskets

Abstract Flexible graphite-based gaskets are used extensively in high-temperature applications as a replacement for asbestos-based gaskets. The effects of aging and temperature exposure on flexible graphite sheet gaskets were the subject of a previous work (Derenne et al., 1997, “Elevated Temperature Characterization of Flexible Graphite Sheet Materials for Bolted Flanged Joints,” Welding Research Council Bulletin, Issue 419, pp. 1–87.). In this paper, the effects of aging on flexible graphite under a confined-gasket configuration will be examined as they are yet unknown. This study outlines the performance evaluation of the elevated temperature behavior of flexible graphite-based gaskets under a confined configuration and long-term exposure employing a high-temperature aged leakage relaxation (HALR) fixture. This aged relaxation leakage adhesion test (ARLA)-like fixture retains the mechanical features of the aged tensile relaxation screening (ATRS)/high-temperature aged tensile relaxation (HATR) while enabling cold leakage rate and weight loss measurements. Four distinct semimetallic gaskets with different graphite-confined configurations, namely, corrugated metal, spiral wound, kammprofile, and double jacketed, were evaluated within a temperature range of 800–1200 °F (430–650 °C) for an exposure time of 2500 h. Graphite weight loss, gasket thickness change, leakage and tightness parameters, and creep and relaxation measurements were taken at regular intervals for each gasket style. To better assess the aging process, these critical mechanical and leakage properties were scrutinized; the influence of the degradation process, related mainly to graphite oxidation, was emphasized.

Manganese – iron coated flexible graphite sheet having wide potential window for energy storage devices

Due to their high-power density, manganese-based electrodes have been studied for energy storage systems. However, they are not stable over high potential windows limiting their use as supercapacitor electrode materials. Manganese was electrodeposited with iron to increase the potential window because manganese-based electrodes are electroactive in the positive region (in Na2SO4 electrolyte) whereas iron-based electrodes are electroactive in the negative region. Graphite was coated potentiostatically with Mn-Fe alloys in a deep eutectic solvent (DES) ionic liquid, Ethaline. The effect of deposition potential on surface morphology, chemical structure, and electrochemical behavior was investigated. XRD, Raman, FTIR, CV and SEM were utilized to characterize bare graphite and alloy deposited graphite. The areal capacitance of the alloy-coated graphite electrode was determined to be 1.66 F cm−2 at 5 mV s−1. The potential window of the alloy-based coating electrodeposited from Ethaline DES was 2.0 V (from −1.0 to +1.0 V). The Mn-Fe-coated graphite electrode material reacts with the neutral electrolyte via a combination of surface-controlled and diffusion-controlled mechanisms. The production of Mn-Fe-coated graphite electrodes from ionic liquid (Ethaline) media allowed for flexible, easy-to-prepare, and cheap electrodes with wide potential windows for supercapacitor applications.

Low-Cost Flexible Graphite Monopole Patch Antenna for Wireless Communication Applications

This research investigates a monopole patch antenna for Wi-Fi applications at 2.45 and 5.2 GHz, and WiMax at 3.5 GHz. A low-cost and flexible graphite sheet with good conductivity, base on graphite conductive powder and glue is used to create a radiator patch and ground plane. Instead of commercially available conductive inks or graphite sheets, we use our self-produced graphite liquid to create the graphite sheet because it is easy to produce and inexpensive. The antenna structure is formed using a low-cost and easy hand-screen printing approach that involved placing graphite liquid on a bendable polyester substrate. This research focuses on designing and developing a low-cost, thin, light, and flexible patch antenna for wireless communication and smart glass applications. The proposed antenna utilizes CST microwave software for simulations to improve the parameters before fabrication and measurement. The simulation and measurement results for the reflection coefficients at 2.45 GHz, 3.5 GHz, and 5.20 GHz are reliable and cover the required resonance frequencies, antennas gain are 1.91, 1.98, and 1.87 dB, respectively. Additionally, the radiation patterns of both results are omnidirectional. In the experiments, bending the proposed patch antenna along with the cylinder with the radii of 60, 40, and 25 mm yielded the same measurement results as the unbent patch antenna.

New Thermal Design Strategy to Achieve an 80-kg-Class Lightweight X-Band Active SAR Small Satellite S-STEP

The main objective of the S-STEP (the Small Synthetic Aperture Radar (SAR) Technology Experimental Project (S-STEP)) mission is developing an 80-kg-class active X-band SAR observation small satellite. For lighter, smaller, better, and cheaper development of the S-STEP system, a new thermal design strategy is essential. Therefore, we proposed a new thermal design strategy in this study. The main features of the proposed thermal design involve the minimization of heater power consumption by optimizing environmental heat fluxes on the satellite, the provision of long-term SAR imaging duration in both right- and left-looking modes, and the use of a lightweight flexible graphite sheet as a thermal interface for some high-power instruments. These features contribute to minimizing the satellite’s mass budget through heater power minimization and achieving on-orbit system performance of S-STEP. The effectiveness of the proposed thermal design was numerically verified by on-orbit thermal analysis of the S-STEP system. In addition, the thermal design on a key payload component and the multifunctional transmit/receive module structure were verified through a space-simulated thermal vacuum test.

Three-dimensional Si / vertically oriented graphene nanowalls composite for supercapacitor applications

Three-dimensional (3D) carbon nanostructures are promising architectures to improve both specific capacity and power density of electrochemical energy storage systems. Their open structure and porosity provide a large space for active sites and high ion diffusion rates. To further increase their specific capacity, they can be combined with metal oxides. However, this combination often results in the loss of cycling stability and power density. Among the different electrode materials being studied, vertically oriented graphene nanowalls (VG) have recently been put forward as a potential candidate. Here, we report the use of VG covered by Si for increased supercapacitor performance. VG were grown on flexible graphite sheet (FGS) substrate by inductively coupled plasma chemical vapor deposition (ICP-CVD). Furthermore, silicon (Si) was deposited by magnetron sputtering on VG and the electrochemical performance studied in ionic liquid (IL) electrolyte. The incorporation of Si in VG/FGS provides an areal capacitance up to 16.4 mF cm−2, which is a factor 2 and 1.4 greater than that of bare substrate and VG/FGS, respectively. This increase in capacitance does not penalize the cycling stability of Si/VG/GS, which remains outstanding up to 10,000 cycles in IL. In addition, the relaxation time constant decreases from 9.1 to 0.56 ms after Si deposition on VG/FGS.

Vertically Aligned ZnO/MnO2/Pedot Core-Shell Electrode in 3-D Nano-Architecture for High Energy-Power Density Pseudocapacitive Electrochemical Energy Storage

Electrochemical capacitors have emerged as the favored energy storage technology in diverse applications like hybrid electric vehicles, portable electronics, communication and smart grids. The key challenge is to increase the energy density alongside the high power density. The structured carbons based electrical double layer capacitors are common but fail to meet this requirement. The Faradaic charge storage mechanism based pseudo-capacitors offer enticing opportunities to bridge the energy and power density functionality gap between the battery and supercapacitors. One approach is to use conducting polymers (CPs), poly 3,4-ethylenedioxythiophene (pedot), polypyrrole and polyaniline etc wherein Faradaic processes are visualized as doping-dedoping of counter ions across vast interface with electrolyte. The other approach is to utilize reversible redox process exhibited by transition metal oxides (TMO) such as RuO2, MnO2 NiO, V2O5 etc which due to multivalent cation states and fast ions/electron kinetics can exhibit high charge storage capability. TMOs could have specific capacitance > 1000 Fg-1 but low electrical conductivity and low cycle stability are the main impediments. Conducting polymers have high electrical conductivity, but have poor mechanical strength and cyclic ability. Most past researches have tried to overcome these deficiencies in TMOs and ECPs by forming composite with carbon nanotubes, graphene etc. In this work we have investigated the metal oxide and conducting polymer composite electrode created in a specific nano-architecture that takes advantage of synergy of their potent properties coupled with the short ion diffusion paths and efficient electron exchange during redox processes.By hierarchical integration, supercapacitor electrodes in the 3-dimensional core-shell nanostructure have been designed based on ZnO nanorods at the core, redox active MnO2 layer and surface electro-polymerized pedot conducting polymer as shell. The vertically aligned ZnO nanorods array were hydrothermally grown over flexible graphite sheets to form the core template (Fig 1a). The ZnO nanorods were decorated with a thin ~120 nm layer of MnO2 nanoflakes by KMnO4+MnSO4 solution dip process to form an initial shell nanostructure. A microporous 250 nm thin layer of pedot was molecularly formed by insitu electro-pulsed polymerization over MnO2 surface to create a bi-layer shell (Fig 1b). The pedot shell with controlled porosity was achieved by short 10 ms high current (4 mA.cm-2) pulsed polymerization in aqueous solution of edot monomer, LiClO4 dopant and sodium dodecyl sulfate (SDS) surfactant. The ZnO / MnO2/ pedot core-shell nanostructure electrode shortens the ion diffusion path for fast ionic transport and renders large electroactive sites due to vast surface area. Pedot shell facilitates electronic transfer and ZnO core and imparts structural stability beside large surface area. The electrochemical energy storage performance of ZnO core, ZnO/MnO2 and ZnO/MnO2/Pedot core-shell electrodes was analyzed by cyclic voltammetry (CV), impedance spectroscopy (EIS), charge-discharge (CD) and long term cyclic tests in a three-electrode cell with Pt sheet as counter and Ag/AgCl as reference electrode in aqueous 1M sodium sulfate mediumThe Raman spectra analysis shows MnO2 shell forms in birnessite Mn(IV) state uniformly over ZnO nanorods. The pedot is highly conjugated (ClO4 ions) with sufficient micro-porosity for MnO2 to access electrolyte (LiClO4) and possible Li-ion incursion in pedot and MnO2. CV analysis establishes redox behavior of ZnO-MnO2 core-shell and with pedot shell further increase in areal capacitance >1090 F.g-1 with near rectangular CV plots (Fig 2a). The scan rate dependent study of surface charge and ion diffusion limitation shows that pedot layer mitigates poor electronic conduction in MnO2 shell and provided diffusive pathways for the ions thus enhancing capacitive properties (Fig 2b). This is further affirmed from the Nyquist plots showing nonexistent Warburg region indicating inconsequential diffusion limitation and the near vertical imaginary impedance indicating high pseudocapacitance. The 1.0- 3.0 mA cm-2 CD plots of ZnO/MnO2/pedot core-shell electrodes are triangular with minimal resistive drop and ~91% Coulomb efficiency. The ZnO/MnO2/core-shell shows energy density of 25.6 Wh kg-1 and power density 2.6 kW kg-1 and a significantly improved rate capability is realized with added pedot shell as evidenced by power density 20.8 kW.kg-1 corresponding to energy density of 37.9Wh.kg-1 .The cyclic stability tested over 6000 CD cycles show the usual capacitance fading for 900 cycles and highly stable performance thereafter and perhaps beyond 6000 cycles as the CD plots were in triangular without any change in resistive drops (Fig 2c). The supercapacitor device based on two symmetrical ZnO/MnO2/core-shell electrodes was similarly investigated. This paper will report on the significant research findings on the synergistic electrochemical action of nano MnO2 with molecularly integrated microporous pedot over ZnO nanorod array in a 3-dimensional nanoarchitecture Figure 1

Spatially localized measurement of isotropic and anisotropic thermophysical properties by photothermal radiometry

This work presents the development of a new photothermal radiometry (PTR) setup using a mix between frequency and spatial domain scans, along with a three-dimensional (3D) heat diffusion model. This newly developed PTR system, with a spatial resolution of 33 μm, is used to measure thermophysical properties of several kinds of materials. These properties include the thermal diffusivity, a, of homogeneous semi-infinite materials, thermal boundary resistance, Rth, and thermal anisotropy of membranes. The measured properties for homogeneous semi-infinite materials and two-layered systems are in good agreement with the literature values. In addition, it was possible to obtain an anisotropic factor of 24.6 between the in-plane and cross-plane thermal diffusivity of a 25 μm anisotropic flexible graphite sheet. Furthermore, it was also possible to measure, both directly and independently, the anisotropic thermal diffusivities for a 1 μm titanium membrane. It is suggested that this new hybrid technique can help us to fill the gap between conventional PTR and other photothermal and thermoreflectance techniques. Using this PTR setup, it is possible to experimentally measure isotropic and anisotropic thermophysical properties of bulk and thin materials, including membranes, with high precision through accurate characterization of the pump beam spots size. This is accomplished without the need for an optical transducer layer.

Functionalization of Self-supporting Graphene with a High Grafting Yield for Hydrophilicity Improvement

Abstract The functionalization of self-supporting graphene (SSG) which in-situ grows on a flexible graphite sheet is performed by an electrochemical exfoliation in a HCl solution and then a diazonium reaction using p-aminobenzenesulfonic acid. The functionalized SSG is defined as F-SSG. The grafting yield of benzenesulfonic acid groups on F-SSG is up to 7.5%. The conductivity of the F-SSG is 502.7 S/cm. The water contact angle of F-SSG is only 28.6°, which is much smaller than that of SSG, displaying good hydrophilicity.

Amorphous NiFe–OH/Ni–Cu–P supported on self-supporting expanded graphite sheet as efficient bifunctional electrocatalysts for overall water splitting

With the serious intensification of energy shortage and greenhouse effect, people begin to look for the sustainable energy sources to replace fossil energy sources. Herein, self-supporting expanded graphite sheet (SSEGS) was developed as an ideal catalyst support through electrochemically intercalating flexible graphite sheet in alkaline solution. Electroless deposition was employed to synthesize Ni–Cu–P alloy on SSEGS and then an amorphous NiFe hydroxide/Ni–Cu–P/SSEGS (NiFe–OH/Ni–Cu–P/SSEGS) composite catalyst was further constructed through electrodeposition. Benefitting from the unique structural advantage of SSEGS and the synergistic effect between two amorphous Ni-based materials (Ni–Cu–P alloy and NiFe–OH), the resulting electrode exhibited superior bifunctional electrocatalytic performance in 1 M KOH. For H2 evolution reaction and O2 evolution reaction, the NiFe–OH/Ni–Cu–P/SSEGS composite catalyst could reach 10 mA cm−2 at low overpotentials of 75 and 240 mV, respectively. Remarkably, the two-electrode system driven by NiFe–OH/Ni–Cu–P/SSEGS as the anode and cathode could afford 10 mA cm−2 at a low cell voltage of 1.56 V vs. RHE. And after the 12 h stability test, the cell voltage at 10 mA cm−2 increased by only 7 mV, indicating that the two-electrode system had excellent stability. The preparation of NiFe–OH/Ni–Cu–P/SSEGS material with superior bifunctional electrocatalytic performance has a significance influence to the development and expansion of hydrogen production technology.

Simultaneous electrochemical preparation and reduction of graphene with low oxygen content and its electrochemical properties for high-performance supercapacitors

Graphene with low oxygen content via an electrochemically anode exfoliation is desired. Here, an electrochemical exfoliation method to realize the simultaneous electrochemical preparation and reduction of graphene with low oxygen content is proposed using a flexible graphite sheet (FGS). Under water bath, the FGS is soaked into a NaBH4 solution under an electric field of 3 V/cm for 3, 9, 15 or 21 h (Gr-3/Gr-9/Gr-15/Gr-21). The C/O ratios of the FGS, Gr-3, Gr-9, Gr-15 and Gr-21 increase in turn by the X-ray photoelectron spectroscopy. The comparison between the electrochemical properties of the FGS, Gr-3, Gr-9, Gr-15 and Gr-21 indicates that the Gr-15 possesses a specific capacitance of 181 F/g and capacitance retention of 93.8% over 3000 cycles, which shows better electrochemical performances than the FGS, Gr-3, Gr-9 and Gr-21. The symmetric supercapacitor based on the Gr-15 achieves an energy density as high as 22.56 Wh/kg at a power density of 0.85 kW/kg.

Preparation and performance of electrochemical glucose sensors based on copper nanoparticles loaded on flexible graphite sheet

A flexible graphite sheet can be used as a self-supported substrate material for sensors owing to its excellent conductivity and flexibility. Copper nanoparticle/flexible graphite sheet self-supporting enzyme-free glucose sensors were prepared by a hydrothermal method using copper sulfate as the elemental copper source and ascorbic acid as the reducing agent. Results indicate that both the molar ratio of copper sulfate to ascorbic acid and the hydrothermal temperature affect the microstructure and sensor performance. The optimal sensor obtained with a ratio of 1:0.5 at 150 oC has a low detection limit of 1.05 μmol/L, and high sensitivities of 7 254.1 μA·mM-1·cm-2R2 = 0.996 1 from 0.1 to 3.4 mmol/L and 3 804.5 μA·mM-1·cm-2 (R2 = 0.999 5) from 3.4 to 5.6 mmol/L The sensor possesses excellent anti-interference properties against sodium chloride, acetaminophenol, ascorbic acid, dopamine, and uric acid, and has good reproducibility.

Application of Atmospheric-Pressure-Plasma-Jet Modified Flexible Graphite Sheets in Reduced-Graphene-Oxide/Polyaniline Supercapacitors.

In this study, flexible and low-cost graphite sheets modified by atmospheric pressure plasma jet are applied to reduced-graphene-oxide/polyaniline supercapacitors. Surface treatment by atmospheric pressure plasma jet can make the hydrophobic surface of graphite into a hydrophilic surface and improve the adhesion of the screen-printed reduced-graphene-oxide/polyaniline on the graphite sheets. After the fabrication of reduced-graphene-oxide/polyaniline supercapacitors with polyvinyl alcohol/H2SO4 gel electrolyte, pseudo-capacitance and electrical double capacitance can be clearly identified by the measurement of cyclic voltammetry. The fabricated supercapacitor exhibits specific capacitance value of 227.32 F/g and areal capacitance value of 28.37 mF/cm2 with a potential scan rate of 2 mV/s. Meanwhile, the capacitance retention rate can reach 86.9% after 1000-cycle cyclic voltammetry test. A light-emitting diode can be lit by the fabricated reduced-graphene-oxide/polyaniline supercapacitors, which confirms that the supercapacitors function well and can potentially be used in a circuit.

Improved electrochemical performance of pyrolytic graphite paper: Electrochemical versus reactive cold-plasma activation

Flexible pyrolytic graphite sheets or graphite paper (GP) are a promising source of disposable (low-cost) electrochemical sensors. This work demonstrates the improvement in the electrochemical performance of graphite paper either after a simple electrochemical activation in acid media using cyclic voltammetry or after cold reactive plasma treatment using CO2 and O2 gases. Cyclic voltammetry of the redox probe ferri-ferrocyanide showed higher electrochemical reversibility on the treated surfaces, which was corroborated by the electrochemical impedance spectroscopy (lower charge transfer resistance). Scanning electron microscopy revealed a high number of grooves on the treated surfaces after both electrochemical and plasma treatments and Raman spectroscopy showed more structural defects (higher D/G ratios), which may explain the improved cyclic voltammetric response of the redox probe. As a proof-of-concept, the graphite paper was evaluated for dopamine detection using cyclic voltammetry and amperometry under flow conditions. Improved performance on treated surfaces, especially after CO2-plasma treatment, was verified. The electrochemical activation is a simple strategy to improve the sensing properties of graphite paper; however, cold-plasma treated surfaces provided better sensing properties probably due to the production of higher number of structural defects.

Thermal decomposition and gas release properties of metal chloride-graphite intercalation compounds prepared utilizing polyimide film-derived graphite sheets

Abstract We have reported that metal chloride-graphite intercalation compounds (GICs) prepared from flexible polyimide film-derived graphite sheets, such as CuCl2-, MoCl5-, and AlCl3-CuCl2-GICs, demonstrate excellent air stability. In this work, the high-temperature thermal stability and gas release properties of those GICs were investigated. MoCl5- and AlCl3-CuCl2-GICs were unstable at high temperatures, exhibiting weight losses at 150 °C and 100 °C, respectively, which accompanied the release of HCl and Cl2 gases. In contrast, the CuCl2-GIC demonstrated relatively high thermal stability in inert atmospheres at temperatures below 400 °C, showing neither weight loss nor gas release. After heat treatment at 600 °C at a heating rate of 5 °C/min, only a slight decrease in the electrical conductivity was observed.

Beneficiation of ultra-large flake graphite and the preparation of flexible graphite sheets from it

Beneficiation of ultra-large flake graphite and the preparation of flexible graphite sheets from it

An electrochemical paper based nano-genosensor modified with reduced graphene oxide-gold nanostructure for determination of glycated hemoglobin in blood

Hemoglobin A1c (HbA1c) is a standard biomarker to measure long-term average glucose concentration for diagnosis and monitoring of diabetes. Various methods have been reported for measuring HbA1c, however, portable and precise determination is still challenging. Herein, a new highly sensitive electrochemical nanobiosensor is developed for the specific determination of HbA1c. A nanocomposite of reduced graphene oxide (rGO) and gold with hierarchical architecture structure was electrochemically deposited on a cheap and flexible graphite sheet (GS) electrode. The nanocomposite increased the surface area, improved the electron transfer on the electrode surface and augmented the signal. It also provided a suitable substrate for linkage of thiolated DNA aptamer as a bioreceptor on the electrode surface by strong covalent bonding. The quantitative label free detection was carried out by differential pulse voltammetry (DPV) in a phosphate-buffered saline (PBS) solution containing redox probe Fe(CN)63−/4-. The detection is based on insulating the surface in presence of HbA1c and decreasing the current, which is directly related to the HbA1c concentration. The nanobiosensor demonstrated high sensitivity of 269.2 μA. cm−2, wide linear range of 1 nM–13.83 μM with a low detection limit of 1 nM. The biosensor was successfully used for measuring HbA1c in blood real sample. Furthermore, it is promising to use it as a part of a point of care device for low-invasive screening and management of diabetes.

Solid-state graphene-based supercapacitor with high-density energy storage using ionic liquid gel electrolyte: electrochemical properties and performance in storing solar electricity

The electrochemical properties and high-density energy storage performance of graphene nano-platelet-based solid-state electrical double-layer supercapacitor device are reported. The graphene device is fabricated with electrolyte comprising of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) room temperature ionic liquid and LiClO4 dopant entrapped within polymer matrix formulated as a gel. The mesoporous graphene electrode was formed via dispersion in amorphous polyvinylidene (PVdF2) host over flexible graphite sheets with minimal graphene layer (< 5-layer) stacking. Exploiting the abundance of charge ion species in the ionic liquid gel electrolyte and pervasive accesses to the graphene platelets via voids, high double-layer specific capacitance of 214 Fg−1 was realized based on cyclic voltammetry data. Impedance studies show a low (0.79 Ω cm2) charge transfer resistance and a short Warburg range indicating highly diffusive ionic transport capability in the ionic liquid gel electrolyte. The Bode analysis showed high figure of merit for pulse power with 1145 ms response time and high-density (27 kWkg−1) pulsed power capability of the graphene supercapacitor. The charge–discharge data show graphene supercapacitor by availing high (~ 2 V) stable potential window in ionic liquid electrolyte gel greatly boosted the energy density to 33.3 Whkg−1 at power density 3 kWkg−1 with minimal decrement to 24.7 Whkg−1 at high ~ 3 Ag−1 discharge current density. By integration with solar cells, direct storage of light-generated electricity and discharge behavior of ionic liquid electrolyte graphene supercapacitor is reported.

Ferrous sulfate as an in-situ anodic coagulant for enhanced bioelectricity generation and COD removal from landfill leachate

Landfill Leachate is a heavily contaminated wastewater. MFCs (Microbial Fuel cells) are unique bioreactors, which utilize the catalytic activity of microbes for converting the chemical energy stored in organic-rich streams for bioelectricity production. MFCs represent an auspicious technology to treat landfill leachate and generate bioelectricity. Here, we evaluated the addition of ferrous sulfate as anodic coagulant as well as a media component to enhance the MFC performance. The Box-Behnken Design model of Response surface methodology (RSM) was found suitable for the determination of optimal conditions for the removal of chemical oxygen demand (COD). COD removal of 78.6% was achieved with coagulation alone at pH 8, reaction time of 90 min, and a coagulant dose of 3 g/L. Ferrous sulfate addition to MFC, significantly improved COD removal. 99.6% removal of total COD was achieved from 75% of landfill leachate, at a retention period of four days; whereas, with 100% leachate as anodic feed, 98.7% COD was removed on the third day. The volumetric power density of 6644.6 mW/m3 was achieved without any catalyst using flexible graphite sheets as electrodes. This study revealed that the integration of coagulation with MFC technology enhanced the treatment efficiency as well as power generation for landfill leachate.