Exfoliated Graphite Electrode Research Articles

Exfoliated Graphite: A Surface Renewed Electrode for Environmental Applications

Exfoliated graphite is a 2D carbon material that has recently received great attention owing to its remarkable analytical merits such as fast electron migration, ease of surface regeneration, high-temperature resistance, ability to withstand high-current density, excellent conductivity, and sensitivity. Due to its excellent analytical signature, an exfoliated graphite electrode has been reportedly used in the construction of sensors and biosensors for various applications. This electrode can be used alone or blended with several nanomaterials/semiconductors for the degradation of various organic pollutants in wastewater. Despite the outstanding results reported in the use of exfoliated graphite electrodes for various analytical applications, very few reports were documented in the literature. Therefore, this review elaborated on the importance of exfoliated graphite electrodes for electrochemical analysis.

Dependence of capacitive properties of an EDLC on exfoliation time of graphite electrodes

The scientific focus has been directed through the production and application of “wonder material-graphene” after its discovery in 2004. But the mass production cost has become a huge disadvantage towards commercializing graphene-based manufactures. As alternative low-cost material, exfoliated graphite (EG) has emerged to be a novel nanostructured carbon material with a potential for electrochemical energy storage device applications owed to its unique characteristics similar to graphene. In this study a series of EG samples were prepared by a surfactant-mediated liquid-phase exfoliation method by changing the exfoliation time. Electrochemical double-layer capacitors (EDLCs) were fabricated using different EG samples as an electrode material and a gel polymer electrolyte (GPE). They were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge discharge (GCD) techniques. EDLC having EG electrodes of 10 h exfoliation time showed the highest results with single-electrode specific capacitance (Csc) of 4.12 F g−1, single-electrode specific discharge capacitance (Csd) of 1.10 F g−1, and relaxation time of 0.22 s from CV, GCD, and EIS, respectively.

Methanol Oxidation in Alkaline Media with Pt-Au/fMWCNTs and Pt-Pd/fMWCNTs Electrocatalysts on an Exfoliated Graphite Electrode

The poisoning of pure platinum electrodes has propelled the improvement of platinum-based alloy catalysts. In this work, we report the application of exfoliated graphite electrode as an anode platform for binary platinum-based electrocatalysts for methanol oxidation in alkaline media. Platinum-based binary electrocatalysts comprising of Pt-Au and Pt-Pd nanoparticles on functionalized multi-walled carbon nanotubes (MWCNTs) support were synthesized via polyol process. The nanocomposite electrocatalysts (Pt-Au/fMWCNTs and Pt-Pd/fMWCNTs) were characterized by transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffractometer (XRD). The electrochemical activity of the Pt-Pd/fMWCNTs and the Pt-Au/fMWCNTs electrocatalysts was assessed utilizing cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in the presence of methanol. The nanoparticles were in the size regime of 3 to 5 nm and the XRD affirmed successful functionalization of the MWCNT and its impregnation with the binary Pt nanoparticles. The electrooxidation of methanol in alkaline conditions was seen with a high current density of about 26.1 mA cm−2 on Pt-Au/fMWCNTs and 13.52 mA cm−2 on Pt-Pd/fMWCNTs electrocatalysts deposited on exfoliated graphite working electrodes. The exfoliated graphite platform is a promising electrode for fuel cell application.

Exfoliated Graphite Electrodes for Organic Single-Crystal Field-Effect Transistor Devices

In this work, exfoliated graphite was used as an electrode for organic single-crystal field-effect transistor (FET) devices, and the electrode performance was demonstrated. The reduced rigidity of ...

An Exfoliated Graphite-Based Electrochemical Immunosensor on a Dendrimer/Carbon Nanodot Platform for the Detection of Carcinoembryonic Antigen Cancer Biomarker.

An electrochemical immunosensor for the quantification of carcinoembryonic antigen (CEA) using a nanocomposite of polypropylene imine dendrimer (PPI) and carbon nanodots (CNDTs) on an exfoliated graphite electrode (EG) is reported. The carbon nanodots were prepared by pyrolysis of oats. The nanocomposites (PPI and CNDTs) were characterized using X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The proposed immunosensor was prepared on an exfoliated graphite electrode sequentially by drop coating CNDTs, the electrodeposition of G2-PPI (generation 2 poly (propylene imine) dendrimer), the immobilization of anti-CEA on the modified electrode for 80 min at 35 °C, and dropping of bovine serum albumin (BSA) to minimize non-specific binding sites. Cyclic voltammetry was used to characterize each stage of the fabrication of the immunosensor. The proposed immunosensor detected CEA within a concentration range of 0.005 to 300 ng/mL with a detection limit of 0.00145 ng/mL by using differential pulse voltammetry (DPV). The immunosensor displayed good stability and was also selective in the presence of some interference species such as ascorbic acid, glucose, alpha-fetoprotein, prostate-specific antigen and human immunoglobulin. Furthermore, the fabricated immunosensor was applied in the quantification of CEA in a human serum sample, indicating its potential for real sample analysis.

Si(-silicide) embedded in highly elastic exfoliated graphite nanocomposite anode materials produced by high-energy mechanical milling for lithium-ion secondary batteries

Silicon-based nanocomposite materials have attracted noteworthy attention as a potential anode material for the lithium-ion rechargeable batteries. However, volume changes of the Si during the lithiation/delithiation result in inferior capacity retention and poor coulombic efficiency. In this work, we report a novel nanocomposite Si-FeSi2/EG in which nano-scale Si-FeSi2 powders encapsulated in the exfoliated graphite (EG) synthesized by a scalable two-stage high-energy mechanical milling. Structure and microstructure of the nanocomposite are investigated by XRD, FE-SEM, and HR-TEM. The morphology of the Si-FeSi2/EG nanocomposite reveals the random distribution of Si-FeSi2 in the EG. The nano-indentation results revealed that the Si-FeSi2/EG electrode exhibited significant elastic recoverable energy as compared to the Si and the Si-FeSi2. Remarkably, the Si-FeSi2/EG nanocomposite demonstrates a stable reversible capacity of ∼1002 mAh g−1 even at 50th cycle with a coulombic efficiency ∼99.8%. The irreversible capacity loss of Si-FeSi2/EG anode after the 1st, 3rd and 50th cycle was 21, 2.2 and 0.2, respectively. The significant cyclic performance was mainly ascribed to the silicon crystal size reduction and highly elastic Si-FeSi2/EG nanocomposite due to encapsulation of the Si-FeSi2 in the exfoliated graphite.

Voltammetric Analysis of As(III) at a Cobalt Nanoparticles/Reduced Graphene Oxide Modified Exfoliated Graphite Electrode

Voltammetric Analysis of As(III) at a Cobalt Nanoparticles/Reduced Graphene Oxide Modified Exfoliated Graphite Electrode

Hybrid Iron Oxide on Three‐Dimensional Exfoliated Graphite Electrode with Ultrahigh Capacitance for Energy Storage Applications

AbstractElectrode materials with low cost, large theoretical capacity, and fast ion/electron transport rate are highly desirable for capacitive applications. Pseudocapacitive iron oxide materials (e. g., Fe2O3, Fe3O4) satisfy the first two aspects, but are electrically/ionically insulating, hindering their practical applications in energy storage. Here, hybrid mesoporous iron oxide (Fe2O3/Fe3O4) materials are integrated with a three‐dimensional electrochemically exfoliated graphite substrate (EG) using an electrodeposition coupled with a post‐chemical transition strategy. The hybrid Fe2O3/Fe3O4 materials on EG exhibit an ultrahigh specific capacitance of 1530 F g−1 at current density of 1 A g−1. This material with such high capacitance ranks on the top of the reported iron oxide materials for capacitive applications. In addition, the assembled device with EG@Fe2O3/Fe3O4 as anode can deliver a high gravimetric energy density of 21.6 Wh kg−1 at a power density of 225 W kg−1, based on the total mass of the two electrodes (including the mass of the current collectors). This system can power various electronic devices, suggesting its great potential for energy storage applications.

Towards wastewater treatment: Photo-assisted electrochemical degradation of 2-nitrophenol and orange II dye at a tungsten trioxide-exfoliated graphite composite electrode

The degradation of organics in water treatment by electrochemical and photo-assisted electrochemical processes was carried out using a photoanode consisting of tungsten trioxide (WO3) and exfoliated graphite (EG). The WO3-EG nanocomposite was characterised using voltammetry, X-ray diffractometry, Raman and FTIR spectroscopy, and scanning electron microscopy connected to energy dispersive X-ray spectrometry. The applicability of the WO3-EG as photoanode material was investigated by the degradation of 2-nitrophenol and orange II dye as model organic pollutants in a 0.1M Na2SO4 solution, using a 10mAcm−2 current density. The removal efficiencies and the extent of mineralisation of the dye and 2-nitrophenol were monitored using a UV–Visible spectrophotometer and a TOC analyser respectively. The results showed that the WO3-EG nanocomposite electrode gave a higher removal efficiency (82% for 2-nitrophenol and 95% for orange II dye) and a higher degree of mineralisation (69% for 2-nitrophenol and 67% for orange II dye) in comparison to the EG electrode. Furthermore, efforts were made to evaluate the degradation intermediates which indicated the formation of carboxylic acids that were further degraded by hydroxyl radicals.

Metal Free Composite Electrodes for Hydrogen Evolution Reaction

Hydrogen production by splitting of water, employing various energy sources has been studied intensely. To date, the cathode (H2 production electrode) used for electrochemical method of water splitting has been platinum. Use of platinum hampers the commercialization of such devices due to overall high expense. Under such a scenario, polythiophene and its derivatives coated over exfoliated graphite (EFG) were considered as an alternative to platinum electrode. This can improve both the efficiency in water splitting as well as the cost-factor. Thiophene and its derivatives were electropolymerized over flexible exfoliated graphite electrode. Scanning Electron Micrographs confirmed the presence of polymerized layer over EFG. The electrochemical results showed considerable enhancement in protection against carbon oxidation in exfoliated graphite and also an overall lowering of the onset potential of water splitting under light irradiation.

Electrochemical co-detection of As(III), Hg(II) and Pb(II) on a bismuth modified exfoliated graphite electrode

The applicability of a bismuth modified exfoliated graphite (EG) electrode for the co-detection of heavy metal ions -As(III), Hg(II) and Pb(II)-in water samples using square wave anodic stripping voltammetry (SWASV) is reported. Bismuth nanoparticles were deposited on an EG electrode potentiostatically at −1000mV for 300s to form EG-Bi electrode. The Bi modified EG electrode was characterised in 5mM ferrocene and used to as an electrochemical sensor for Pb(II) and Hg(II) individually in 0.1M acetate buffer solution (pH 5) with detection limits (LODs) of 0.83μgL−1., 0.46μgL−1 and limit of quantification of 2.8μgL−1 and 1.5μgL−1 respectively. Simultaneous detection of Pb(II), As(III) and Hg(II) was also performed with LODs of 0.053μgL−1, 0.014μgL−1, 0.081μgL−1 and LOQs of 0.18μgL−1, 0.047μgL−1 and 0.27μgL−1 for Pb(II), As(III) and Hg(II) respectively. All the detections were performed under optimised experimental conditions. The stability of the EG-Bi sensor was tested and the electrode was applied to environmental samples. The results found with this method were comparable with those obtained with inductively coupled plasma – optical emission spectrometric technique.

An Exfoliated Graphite Based Electrochemical Sensor for As(III) in Water

AbstractIn this work, we present the application of an exfoliated graphite electrode modified with gold nanoparticles (AuNPs) for the detection of As(III) in acidic media. Gold nanoparticles were deposited on the surface of an exfoliated graphite electrode by electrodeposition at a potential window of −0.2 V to 1.2 V. This was followed by activation in 0.5 M H2SO4 with 10 cycles from 0.6 V to 1.4 V. The modification of exfoliated graphite (EG) showed an increased electroactive surface area of the electrode and improved peak current output in a Fe(CN)63−/4− redox probe. EG‐AuNPs electrode was used to detect As(III) in 1.0 M HNO3 using square wave anodic stripping voltammetry (SWASV) technique at optimum conditions of pH 3, deposition potential of −0.8 V, deposition time of 180 s, frequency of 5 Hz and pulse amplitude of 50 mV. The EG‐AuNPs electrode detected As(III) in solution to a limit of 0.58 ppb with regression of 0.9993. The method reported is simple, cheap and possesses good reproducibility. The developed electrochemical sensor was applied in the detection of As (III) in an industrial real water sample. The results of the real water sample analysis from the developed method are comparable with the inductively coupled plasma – optical emission spectroscopy (ICP‐OES) results.

Multiple anodic regeneration of exfoliated graphite electrodes spent in the process of phenol electrooxidation

The present paper deals with the studies concerning anodic regeneration of exfoliated graphite (EG) electrodes coated with oligomer products of incomplete phenol electrooxidation. The electrochemical activity of regenerated samples depends on the concentration of regenerating electrolyte and potential applied during the regeneration. The effective method of a single-step regeneration of spent EG electrodes was found to be anodic treatment proceeded in 6 M KOH at the potential of 1.3 V vs. Hg/HgO/0.5 M KOH. During the oxidative regeneration of EG, the physical and chemical interactions between intensively generated active oxygen and/or OH· radical and oligomer covering the EG surface take place. As has been proved by FTIR and XPS analyses, active oxidative agents cause significant modification of chemical composition of oligomer that resulted in enhanced concentration of surface functionalities mainly involving C=O bonds. The results of multiple regeneration of EG electrode, considered as promising method for practical application, showed that the highest efficiency of regeneration is attained due to potentiostatic treatment carried out in 6 M KOH at the potential of 1.2 V. The electrochemical activity of EG regenerated at this potential increases gradually with the number of regenerating loops and after the third regeneration is almost fourfold higher compared to that of the original EG.

Synthesis, characterisation and application of an exfoliated graphite–diamond composite electrode in the electrochemical degradation of trichloroethylene

A composite electrode made up of exfoliated graphite (EG) and diamond was prepared for the electrochemical oxidation of trichloroethylene (TCE). The SEM images of the EG–diamond material showed that diamond powders were dispersed on the surface of EG materials. The N2 adsorption–desorption isotherm of EG–diamond material resulted in a poor adsorption capability due to the insertion of diamond powders into the porous matrix of EG. Raman spectroscopy revealed the presence of characteristic sp3 bands of diamond confirming good interaction of diamond with EG. Electrochemical characterisation of EG–diamond in 0.1 M Na2SO4 resulted in an enhanced working potential window. The EG–diamond electrode was employed for the electrochemical oxidation of trichloroethylene (0.2 mM) in a Na2SO4 supporting electrolyte. The EG–diamond, in comparison to the pristine EG electrode, exhibited a higher removal efficiency of 94% (EG was 57%) and faster degradation kinetics of 25.3 × 10−3 min−1 showing pseudo first order kinetic behaviour. Under the optimised conditions, 73% total organic content (TOC) removal was achieved after 4 h of electrolysis. The degradation of TCE was also monitored with gas chromatography-mass spectrometry. Dichloroacetic acid (DCAA) was identified as a major intermediate product during the electrochemical oxidation of TCE. The electrochemical degradation of TCE at the EG–diamond electrode represents a cost effective method due to the ease of preparation of EG–diamond composite material without the necessity of diamond activation which is normally achieved through doping.

Reactivities of Modified and Unmodified Exfoliated Graphite Electrodes in Selected Redox Systems

Reactivities of Modified and Unmodified Exfoliated Graphite Electrodes in Selected Redox Systems

An Exfoliated Graphite-Based Bisphenol A Electrochemical Sensor

The use of an exfoliated graphite (EG) electrode in the square wave voltammetric detection of bisphenol A (a model phenolic pollutant) in water, whereby the phenolic electrode fouling challenge is mitigated, is described. The oxidation peak of BPA was observed at about 0.45 V in phosphate buffer solution at pH 10. The current response exhibited a linear relationship with the concentration over a range from 1.56 μM–50 μM. The detection limit was calculated to be 0.76 μM. The EG electrode surface was renewed after each measurement with excellent reproducibility. A real sample application was also investigated.

Degradation of methyl orange in artificial wastewater through electrochemical oxidation using exfoliated graphite electrode

Degradation of methyl orange in artificial wastewater through electrochemical oxidation using exfoliated graphite electrode

Degradation of methyl orange in artificial wastewater through electrochemical oxidation using exfoliated graphite electrode

Exfoliated graphite (EG), with good electronic conductivity, was used as an anode material for the electrochemical degradation of methyl orange (MO), an artificial textile wastewater. Through the electrochemical degradation, 98.6% color removal and 58.5% chemical oxygen demand reduction was achieved at a pH of 2.0, a current density of 13 mA·cm −2, an electrolyte (NaCl) concentration of 0.1 mol·dm −3 and an electrolysis time of 20 min. The degradation is based on chemical adsorption and electro-oxidation. MO molecules are first adsorbed on the EG surface by hydrogen bonds between the -OH functional groups on EG and the MO molecules, which are then degraded by electrochemical oxidation. EG can therefore be regarded as an excellent material for the treatment of textile wastewater.

Electrochemical detection and removal of lead in water using poly(propylene imine) modified re-compressed exfoliated graphite electrodes

Modification of exfoliated graphite (EG) electrode with generation 2 poly(propylene imine) dendrimer by electrodeposition resulted in an electrochemical sensor which was used to detect lead ions in water to a limit of 1 ppb and a linear response between 2.5 and 40 ppb using square wave anodic stripping voltammetry (SW-ASV). Pb(II) was also removed from spiked water sample using a 40-mm diameter unmodified EG electrode with an applied potential of −1,000 mV for 180 min. A removal efficiency of 99% was calculated from a 150 mL sample. The results obtained in both cases using SW-ASV, correlated with atomic absorption spectroscopy.

The electrochemical behaviour of an exfoliated graphite electrode in simulated seawater containing oil

An exfoliated graphite (EG) electrode was prepared and the electrochemical response to oil in simulated seawater was studied by means of the potential step technique and electrochemical impedance spectroscopy (EIS). The capacitance and other electrochemical characteristics of the electrode were affected by the presence of oil. The effects of temperature and salinity on the electrochemical behaviour of the EG electrode in NaCl solution containing oil were investigated by EIS. The results showed that the higher the temperature or the salinity, the higher the double layer capacitance of the electrode.