Graphite Foil Electrode Research Articles

Y-Shaped Acceptor-π-Donor-π-Acceptor Configured Anthraquinone-Tethered Phenothiazine Molecular Scaffold for High-Performance Organic Pseudocapacitors.

For the first time acceptor-π-donor-π-acceptor (A-π-D-π-A) based Y-type organic electrode material have been designed and successfully utilized in supercapacitor (SC) application. This Y-type molecular architecture coined as AQ-Im-PTZ-Im-AQ based on anthraquinone (AQ) (A)-imidazole (Im) (π)-phenothiazine (PTZ) (D)-imidazole (Im) (π)-anthraquinone (AQ) (A) in combination with graphite foil (GF). As-fabricated PTZ-Im-AQ/GF and AQ-Im-PTZ-Im-AQ/GF electrode have shown the good energy storage properties in three-electrode supercapacitor system. Moreover, two-electrode symmetric supercapacitor (SSC) device based on AQ-Im-PTZ-Im-AQ/GF electrode exhibited specific capacitance (Csp) of 68.97 F g-1 at 1 A g-1 current density. The specific electron density (ED) of SSC was observed to be 12.06 Wh kg-1 at a specific power density (PD) of 1798.50 W kg-1. The SSC device exhibited 81.62 % of Csp retention after 5000 galvanostatic charge-discharge (GCD) cycles. For real world applications, AQ-Im-PTZ-Im-AQ/GF electrode was tested in symmetric Csp coin cell with applied potential voltage window of -0.4 to 1.0 V was found to be 112.32 F g-1 at 0.5 A g-1. Moreover, it realized high specific capacitance and high energy density of 19.66 Wh kg-1 at 891.94 W kg-1 power density. As a results, AQ-Im-PTZ-Im-AQ/GF make as an attractive electrode material for application in next-generation SCs.

A novel benzoquinone‐azo linked polymer‐based active electrode material for high‐performance symmetric pseudocapacitors

AbstractPseudocapacitors (PSCs) have attracted researcher's attention due to their potential electrochemical performance as the power source for electronic devices. However, to maintain the high electrochemical properties of pseudocapacitive materials becomes critical. Therefore, the active electrode materials design and synthesis is a challenging task. To tackle these problems, herein, we rationally designed new polymer based on benzoquinone with azo linker. The polymer AZO‐BQ‐P was synthesized and tested for their energy storage applications in combination with graphite foil (GF). In three‐electrode supercapacitor (SC) device, the AZO‐BQ‐P/GF electrode exhibits excellent specific capacitance (Csp) of about 306.27 F g−1 at 0.5 A g−1 current density and higher cycling stability. The pseudocapacitive performance of SC cells result from synergistic effect of AZO‐BQ‐P and GF and due to faster electrolyte ion diffusion and increased availability at electrode/electrolyte interfaces. Furthermore, AZO‐BQ‐P/GF electrode was employed to fabricate two‐electrode AZO‐BQ‐P/GF//AZO‐BQ‐P/GF symmetric SC device. The optimal SSC device shows a Csp reaching 200 F g−1 at 0.5 A g−1, which is an impressive value. Also, it exhibits remarkable cycling stability with 86.18% Csp retention after 5000 galvanostatic charging–discharging (GCD) cycles at 3 A g−1. The SSC device applying AZO‐BQ‐P/GF electrode delivers an excellent energy density (ED) of 25.00 Wh kg−1 at 900.00 W kg−1 power density (PD). Thus, the novel polymer design offers efficient electrode materials to enhance the pseudocapacitive electrochemical performance of the SSC device. This concept can be extended for fabricating other electrochemical systems and accelerate its applications for modern electronic devices.

Comparing Two Types of Graphene-Magnetic Nanocomposites with Enhanced Electromagnetic Properties Synthesized by Two Different Exfoliation Methods

This study has focused on comparing the structure, composition, and magnetic properties of two graphene composites synthesized by two distinctive methods of exfoliation, i.e., one-step and simultaneous exfoliation–electrodeposition. Furthermore, the study investigates the effects of these properties on the quality of electromagnetic (EM) shielding in the nanocomposites (NPs). To synthesize the first composite, we use a DC power supply and graphite foil electrodes in an FeSO4·7H2O and NiCl2·6H2O bath. To construct the second composite, we employ an AC power supply and the graphite rod in the FeSO4·7H2O and CuSO4·7H2O bath. The characterization results of these graphene composites attest to the fact that, compared to the first composite, graphene layers in the second composite show fewer defects, higher crystallization, and more layers. These properties in the second composite make the electromagnetic shielding properties of the Gr/CuFe nanocomposite superior to the those of the first one. This provides the Gr/CuFe nanocomposite with remarkable enhanced absorption characteristics, making it particularly suitable to be adopted in high-frequency absorbers.

Vertically aligned graphene prepared by the electrochemical anodization of graphite foil for supercapacitor electrodes

Vertically aligned graphene (VAG) improves the specific capacitance of electric double layer capacitor (EDLC) electrodes, because VAGs increase the specific surface area of electrode and promote ion diffusion. Herein, we demonstrate a facile approach for preparing the VAGs with outstanding areal specific capacitance by electrochemical anodization of graphite foil (GF). As the anodizing time increases, the graphite layers in the anodized GF (AGF) electrodes expand due to ion intercalation and bubbles. Each graphite layer is vertically aligned, resulting in the formation of VAG sheets on the GF surface. The AGF electrode exhibits an excellent specific areal capacitance of 2.79 Fcm−2 at a current density of 2 mAcm−2, which is higher than that of the GF electrode by a factor of 17.43. The EDLC device using AGF electrodes exhibits an outstanding specific areal capacitance of 1.43 Fcm−2 at a current density of 2 mAcm−2 and a favorable cycling stability retaining 90% of its initial capacitance after 2000 cycles at a current density of 20 mAcm−2. This AGF electrode fabrication method is simple, cost-effective, and eco-friendly. We believe that the fabrication of AGF electrodes may be a significant contribution to the development of high-performance supercapacitors as well as the eco-friendly energy industry.

A novel method for synthesis of clay/polymer stabilized silver nanoparticles

Silver nanoparticles were synthesized with clay mineral (montmorillonite)/PVP (polyvinyl pyrrolidone) suspensions using an electrochemical approach. The polymer and exfoliated clay mineral solution protect and prevent aggregation of the silver nanoparticles. The clay mineral component is environmentally friendly and low cost. Unlike other studies, the clay platelets are exfoliated (sheared apart to individual platelets) to expose a much larger surface area and function as supporting material and stabilizer. A prime advantage of this novel approach is that the polymer and layered silicates protected the silver nanoclusters from agglomerating, effectively immobilizing and enhancing contact with the cathode for reduction. An electrochemical approach for nanoparticle synthesis has several advantages; including control and tuning of the experimental parameters, easy set-up, and short synthesis times. Morphology of the silver nanoparticles depended on current density of the electrochemical synthesis. Transmission electron microscopy showed small spherical silver nanoparticles formed at current densities below 1.25 mA/cm2 and silver dendritic formation at current densities greater than 2.5 mA/cm2. Size distribution of nanocomposites in solution measured by dynamic light scattering was 27 nm for the silver nanoparticles. X-ray diffraction was used to measure the crystallite size of the dried powders, which ranged between 10 and 60 nm depending on the experimental parameters. Nanocomposite coatings were also formed on graphite foil electrodes. Dense uniform films of spherical silver nanoparticles were produced at low current densities (<1.25 mA/cm2), while aggregates formed at higher current densities (>2.0 mA/cm2).

Electrochemical synthesis of composite based on polyaniline and activated IR pyrolyzed polyacrylonitrile on graphite foil electrode for enhanced supercapacitor properties

Electroactive composite coating based on polyaniline and activated IR pyrolyzed polyacrylonitrile particles onto anodized graphite foil was developed for the first time. The roughened surface and presence of oxygen-containing groups on the foil surface provide good adhesion of the composite material. The study of coating properties by SEM and XPS techniques showed that the introduction of activated carbon material particles into the coating increases its surface due to the porosity of the polyacrylonitrile-based activated carbon, and facilitates electronic and ion transport during charge-discharge cycles. Electrochemical performance of composite coatings in comparison with polyaniline coating was investigated by methods of cyclic voltammetry and galvanostatic charge-discharge tests. It has been shown that areal capacitance of composite based on activated IR pyrolyzed polyacrylonitrile and polyaniline coating was 2.8 F cm−2, that is by one and a half times higher than this value for polyaniline (1.9 F cm−2). It was demonstrated that there is almost no capacity loss after 1000 charge-discharge cycles.

Porous carbon-coated graphite electrodes for energy production from salinity gradient using reverse electrodialysis

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2wt% of carbon black (Vulcan X-72), 0.8wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)63−) and hexacyanoferrate(II) (i.e., Fe(CN)64−) redox couple and 1M Na2SO4 at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current–voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil<the Ir-coated titanium (Ti) mesh<the Pt-coated Ti plate<the graphite foil. Moreover, the Vulcan-coated graphite foil showed 5–10% higher power density than the metal mesh electrodes. From the polarization curve of the Vulcan-coated graphite foil electrode, it was found that total resistance decreased as thickness and geometric surface area of the electrode increased.

Current Collector Corrosion in Ca-Ion Batteries

With significant improvements in electrical energy storage, researchers could change the way energy is generated and used. One emerging approach is to change the cation that shuttles charge from lithium to calcium. Calcium cations, roughly the same size as Na+, have many attributes that make them a desirable charge carrier for energy storage applications, including deposition voltage and a porous passivation layer. However, system level issues, such as corrosion, have yet to be investigated. Corrosion of the current collectors must be considered whenever you change the electrolyte and we show that this is particularly true for calcium based systems. Reversible charge/discharge behavior that is due to corrosion can be seen with stainless steel in electrolytes containing calcium salts. This reversible behavior is similar to what might be expected from materials that are intercalating Ca, making the interpretation of electrochemical data challenging. We have found that this corrosion reaction requires either carbon black and/or a transition metal oxide to catalyze the reaction, making it more difficult to detect. Unlike stainless steel, Graphite foil electrodes do not show high voltage reactions and can be used as a tool for testing Ca-ion cathode materials, although some reactions at low potentials have been observed.

Electrochemical synthesis of nano-cobalt hexacyanoferrate at a sol–gel-coated electrode templated with β-cyclodextrin

The paper describes the time-dependent evolution of the electrochemical deposition of cobalt hexacyanoferrate (CoHCFe) on graphite foil electrode modified with electrochemically formed sol–gel film doped with β-cyclodextrin to impart porosity. With short-time electrodeposition, cyclic voltammetry (CV) shows a single redox couple typical of nano-sized clusters of CoHCFe, while at longer deposition times the CV’s shape evolves to the classical form of a bulk compound in which there are present two redox couples. The electrode modified with β-cyclodextrin (CD) included in the sol–gel film has an active surface that corresponds to pores created by CD stacks normal to the surface. Hence, the electrochemical formation of CoHCFe starts in these conductive pores; only at long deposition times do the clusters overlap to form moieties with the voltammetric characteristics of bulk CoHCFe.

Evaluation of carbon composite materials for the negative electrode in the zinc–cerium redox flow cell

An investigation into the suitability of three carbon composites as substrates for the negative electrode in the zinc–cerium redox flow cell has been carried out. The composite electrodes examined comprised the use of polyvinylidene fluoride (PVDF) and high density polyethylene (HDPE) as binders for the carbon and the third was a graphite foil electrode of ∼1mm thickness. The zinc deposition process was carried out in a methane sulfonic acid (MSA) electrolyte at 60°C and nucleation studies revealed the growth of the deposits to be instantaneous in this medium. Galvanostatic charge/discharge cycles were performed in order to test the performance of these composite materials under a variety of operating conditions. For all the materials, the highest charge/discharge coulombic efficiencies (∼95%) were found for the highest discharge current densities (200mAcm−2) employed in the study but this falls as the charge period is increased. The effect of solution flow velocity is however less clear. Prolonged zinc charging–discharging cycling on the composite materials revealed that whereas the PVDF-based electrode exhibited no loss in efficiency with cycling (>250), a drastic reduction was observed for the HDPE-based and graphite foil electrodes beyond 70 cycles and this was accompanied by the physical deterioration in the electrode surface.

A graphite foil electrode covered with electrochemically exfoliated graphene nanosheets

We demonstrate a highly efficient and large area synthesis of 2-D graphene nanosheets on the surface of flexible graphite foils by electrochemical exfoliation of graphite in an effective electrolyte, poly(sodium-4-styrenesulfonate) solution. A constant current of 150 mA/cm was applied to the vertically aligned graphite (anode) and copper (cathode) sheet in the PSS electrolyte solution during a preset time for electrolytic surface exfoliation of the graphite sheet; uniform expansion of the graphite foil was observed. This expanded foil was characterized using scanning electron microscopy, confocal laser scanning microscopy, and high-resolution transmission electron microscopy. Furthermore, we demonstrate the ability of this high surface area foil, covered with uniform graphene, to enable improved electrolyte permeability and Li ion transfer, thereby enhancing electrochemical performance of Li ion battery electrodes.

Activated Carbon Cloth as Anode for Sulfate Removal in a Microbial Fuel Cell

By employing the sulfate-reducing bacterium Desulfovibrio desulfuricans we demonstrate the possibility of electricity generation in a microbialfuel cell (MFC) with concomitant sulfate removal. This approach is based on an in situ anodic oxidative depletion of sulfide produced by D. desulfuricans. Three different electrode materials, graphite foil (GF), carbon fiber veil (CFV), and high surface area activated carbon cloth (ACC), were evaluated for sulfide electrochemical oxidation. In comparison to CFV and GF electrodes, ACC was a superior materialfor sulfide adsorption and oxidation and showed significant potential for harvesting energy from sulfate-rich solutions in the form of electricity. Sulfate (3.03 g dm(-3)) was removed from a bacterial suspension, which represented 99% removal. A maximum power density of 0.51 mW cm(-2) (normalized to geometric electrode area) was obtained with a one-chamber, air-breathing cathode and continuous flow MFC operated in batch mode at 22 degrees C.

Direct generation of electricity from sludges and other liquid wastes

Recently it has been shown that electrical energy can be harvested from marine sediments, simply by connection of an electrode (anode) in anaerobic marine sediments to an electrode in the aerobic zone above the sediments. We have now shown that similar applications are available in sludge treatment. Using a reactor with graphite foil electrodes in an aerated aerobic and anaerobic sludge zone, electrical current was generated, and enhanced when an additional organic substrate (acetate) was added. Electron microscopy, x-ray diffraction, and PCR examination of the anode surface showed no surface colonization and no increase in Geobacter relative to a control, indicating that microbial use of the anode as an electron acceptor wa indirect through the use of redox mediators. Given the demonstration of electricity generation from sludge, the potential for similar applications, using other organic waste sources, is evaluated.

Porphyrin-Modified Electrodes as Biomimetic Sensors for the Determination of Organohalide Pollutants in Aqueous Samples

A preliminary examination of a simple and rapid screening method for quantifying a range of toxic organohalides directly in aqueous solution based on their electrocatalytic reduction with a metalloporphyrin catalyst is described. Homogenous catalysis is described as well as heterogeneous catalysis using precipitated cobalt(II) tetraphenylporphine ((TPP)Co) at a graphite foil electrode which permitted the sensitive detection of a wide range of different organohalides, including a number of chemically diverse industrial pollutants such as 1,2,3,4,5,6-hexachlorocyclohexane (lindane) and carbon tetrachloride, representative of haloalkane compounds, haloalkenes such as perchloroethylene, and aromatics, such as 2,4-dichlorophenoxyacetic acid, pentachlorophenol, and the insecticide DDT. The coordinating effect of solvent on the thermodynamics of the Co(II)/(I) electrode reaction is used to practical advantage to build an amperometric detector that is insensitive to interference from oxygen, a parameter that varies considerably in environmental samples. Devices also appear relatively insensitive to the ionic composition of the analyte sample. The work provides the basis for developing a prototype sensor for screening toxic organohalogen pollutants for use in environmental monitoring situations.

Organic phase enzyme electrodes for the determination of hydrogen peroxide and phenol

An amperometric horseradish peroxidase electrode is described for the determination of hydrogen peroxide in organic solvents. The enzyme was co-adsorbed with an electron mediator, hexacyanoferrate(II), to the surface of a graphite foil electrode making reagentless measurement possible. The electrochemical reduction of the enzymatically oxidized mediator was utilized as the analytical signal. The electrode can be operated in dioxane, chloroform and chlorobenzene, the presence of a small quantity of aqueous buffer being essential for activity. On this basis a small, probe-type sensor has been assembled the response of which is linearly related to hydrogen peroxide concentration between 0.05 and 1 mM. A tyrosinase sensor has been constructed by combining a Clark-type oxygen electrode with a membrane bearing adsorbed enzyme. The sensor is capable of measuring between 0.1 and 5 mM phenol in chloroform saturated with aqueous buffer.

Mediated amperometric enzyme electrode incorporating peroxidase for the determination of hydrogen peroxide in organic solvents

An amperometric enzyme electrode incorporating horseradish peroxidase is described for the determination of hydrogen peroxide in organic solvents. The enzyme was co-adsorbed with an electron mediator, potassium hexacyanoferrate(II), on the surface of a graphite foil electrode, making reagentless measurement possible. The electrochemical reduction of the enzymatically oxidized mediator was utilized as the analytical signal. Studies in different solvent systems revealed that the electrode could be operated in dioxane, chloroform and chlorobenzene, the last two providing approximately double the sensitivity of the former. The presence of a small amount of aqueous buffer was essential for sensor activity. During 2 weeks of intermittent use, the sensitivity of the electrode decreased to 40% of its initial value. At least 50 assays could be performed with a single sensor.

Amperometric enzyme electrode for the determination of phenols in chloroform

An enzyme electrode has been developed that operates in chloroform. The enzyme polyphenol oxidase (E.C.1.14.18.1) was used to detect p-cresol via the electrochemical reduction of the product of the enzyme reaction at a graphite foil electrode. The response was linear for p-cresol concentrations of 0–100 μM. After an initial rise from 1.9 to 4.0 μA in the first three assays, the response of the electrode to p-cresol (100 μM) remained stable for 13 consecutive assays. The enzyme electrode lost no activity over 7 weeks' storage in chloroform at 5°C and is sensitive to a broad range of phenols.

Quinoprotein glucose dehydrogenase and its application in an amperometric glucose sensor

Glucose dehydrogenase (GDH), one of the recently discovered NAD(P) +-independent ‘quinoprotein’ class of oxidoreductase enzymes, was purified from Acinetobacter calcoaceticus LMD 79.41 and immobilised on a 1,1'-dimethylferrocene-modified graphite foil electrode. The second-order rate constant (k s) for the transfer of electrons between GDH and ferrocenemonocarboxylic acid (FMCA) in a homogeneous system, determined using direct current (DC) cyclic voltammetry, was found to be 9.4 × 10 6 litres mol −1 s −1. This value of k s for GDH was more than 40 times greater than that for the flavoprotein glucose oxidase (GOD) under identical conditions. Such high catalytic activities were also observed when GDH was immobilised in the presence of an insoluble ferrocene derivative; a biosensor based on GDH was found to produce more than twice the current density of similar GOD-based electrodes. The steady-state current produced by the GDH-based electrode was limited by the enzymic reaction since methods which increased the enzyme loadings elevated the upper limit of glucose detection from 5 mM to 15 mM. The temperature, pH, stability and response characteristics of the GDH-based glucose sensor illustrate its potential usefulness for a variety of practical applications. In particular, the high catalytic activity and oxygen insensitivity of this biosensor make it suitable for in vivo blood glucose monitoring in the management of diabetes.