Edge Plane Pyrolytic Graphite Research Articles

Influence of Carbon Material Properties on Activity and Stability of the Negative Electrode in Vanadium Redox Flow Batteries: A Model Electrode Study

The V2+/V3+ reaction occurring at the negative electrode in the all-vanadium redox flow battery has been identified as performance limiting in the system. Given the complexity of the commercial carbon electrodes typically used for this application, a model electrode approach is adopted in this work to study electrode activity and stability. This was done using edge and basal plane pyrolytic graphite electrodes modified by electrochemical oxidation. Differential electrochemical mass spectrometry was used for the first time in this work to investigate the parasitic hydrogen evolution reaction on the oxidized carbon surfaces. The basal plane surface showed a higher faradaic efficiency for V3+ reduction compared to that for the edge plane surface. The oxidized surfaces were subject to extended cycling, after which the basal electrode showed a dramatic loss in activity compared to the edge surface which was relatively stable. This activity loss was related to the poor mechanical stability of the basal plane su...

A Simple and Highly Selective Determination of Telmisartan at Sodium Dodecyl Sulfate Modified Pyrolytic Graphite Surface

AbstractA simple, facile, selective and cost effective electrochemical method is proposed for the determination of telmisartan (TMS); a drug used for hypertension. A sodium dodecyl sulfate (SDS) modified edge plane pyrolytic graphite (EPPG) is prepared by simple immersion of EPPG in SDS solution at concentration greater than critical micelle concentration (CMC). The modified sensor exhibited superior sensing properties towards the oxidation of TMS. The modified surface was characterized by using the Energy dispersive X‐ray analysis, Field Emission Scanning Electron Microscopy, Electrochemical Impedance Spectroscopy and cyclic voltammetry. The quantitative investigations of the TMS were performed by applying the square wave voltammetry. The micelles of SDS form a pseudo complex with cation radical of TMS and catalyse the oxidation. The proposed sensor shows the linear calibration plot in the concentration range of 5–100 μM with sensitivity 0.2983 μA/μM and the limit of the detection of the sensor was found to be 0.082 μM. The specificity of the developed sensor was also evaluated in the presence of commonly present interfering substances in biological samples. The amount of TMS excreted in urine of the patients undergoing treatment has also been determined. The proposed method can be effectively applied for the investigation of TMS in pharmaceutical formulations and biological samples.

Development of an electroanalytical method to control quality in fish samples based on an edge plane pyrolytic graphite electrode. Simultaneous determination of hypoxanthine, xanthine and uric acid

A simple, rapid and non-expensive method is proposed to determine hypoxanthine (Hx), xanthine (Xa) and uric acid (UA) in untreated fish samples based on an edge plane pyrolytic graphite electrode (EPPGE). The square wave voltammetry was the electrochemical technique used. In addition, the experimental design and multi-response assays were used to optimize the pretreatment of the working electrode. Therefore, the EPPGE is used in the simultaneous determination of these analytes for the first time. The optimal accumulation conditions of the analytes on the surface of the working electrode were obtained through a composite central design. The linear range was from 0.1 to 50μM for Hx and Xa, and from 0.1 to 25.0μM for UA. The limits of detection (LOD) were 0.08, 0.06 and 0.03μM for Hx, Xa and UA, respectively. Recovery assays were made in order to validate the proposed method. Recovery percentages were between 90 and 110%. Therefore, the method is a good, simple and fast option for the simultaneous determination of Hx, Xa and UA in fish samples, allowing to perform a control quality of samples.

Exploring the suitability of different electrode materials for hypochlorite quantification at high concentration in alkaline solutions

A comparison of the electrochemical performance of noble metal, sp2- and sp3-carbon electrodes towards the reduction of concentrated hypochlorite (ClO−; 0.02M–1.88M), an alkaline (pH ~13) and chemically oxidising solution, is presented. Boron-doped diamond (BDD) gave no discernible electrochemical response whilst all other electrodes showed an electrochemically irreversible cathodic response in the following order (most facile electron transfer): Pt>Au>edge-plane pyrolytic graphite (EPPG)≈sp2-carbon containing BDD>basal plane pyrolytic graphite>glassy carbon≈highly-ordered pyrolytic graphite. Reduction at sp2-BDD occurred at a similar potential to EPPG, but with much lower currents, suggesting edge-plane-like sites are the active sp2 sites in this sp2-BDD, but at much lower surface coverage than in EPPG. Finally, both EPPG and sp2-BDD showed linear current versus [ClO−] responses over the concentration range 0.02M–1.41M (R2>0.995).

Determination of Curcumin in Turmeric Sample Using Edge Plane Pyrolytic Graphite Electrode

Phenolic compounds are an important class of the antioxidants and found in several natural products. Research on the phenolic compounds having antioxidant properties present in natural pruducts like fruits, spices and herbs are increased in recent years. Electroanalytical methods have low detection limits very short analysis time and require less budge as well. These advantages make the electroanalytical methods favorable and voltammetric analysis methods are one of the preferred methods in determination of the compounds having antioxidant properties present in different matrices. In this study, curcumin in turmeric samples were quantitatively determined by using edge plane pyrolytic graphite electrode (EPPG) and differential pulse voltammetry. Electrooxidation behaviour of curcumin was also examined by using cyclic voltammetry method. A three electrode electrochemical cell was used for voltammetric analysis. Edge plane pyrolitic graphite (EPPG), was used as working electrode, saturated calomel electrode (SCE) was used as reference electrode and Pt wire electrode was used as counter electrode in the cyclic voltamety and differential pulse voltametry studies. A linear relationship between anodic peak current and curcumin concentration was observed between 0.325 μM to 1.95μM at EPPG electrode with differential pulse voltammetry. Detection limit was calculated as 0,296 μM and the method successfully applied for detection of curcumin amount in a turmeric sample.

Spectroscopic and electrochemical behavior of the novel tetra-2-methyl-pyrazinoporphyrazines

This study presents the synthesis and characterization of novel metal-free (H2Pc) and metallo porphyrazines (magnesium(II) (MgPz), copper(II) (CuPz), iron(II) (FePz), manganese(II) (MnPz) and nickel(II) (NiPz)) substituted with four 2-methylpyrazine groups on the peripheral positions. The spectroscopic properties of newly synthesized porphyrazines were investigated. The electrochemical behaviors of these porphyrazines were also determined in DMSO solution by cyclic voltammetry (CV) and square wave voltammetry (SWV) methods on edge plane pyrolytic graphite electrode (EPPG) electrode.

A poly-(melamine)/poly-(glutamic acid) based electrochemical sensor for sensitive determination of 2-Thioxanthine

A sensitive and selective edge plane pyrolytic graphite sensor, modified using poly-melamine and poly-glutamic acid (p-Mel-Glu/EPPG) co-polymeric film through a single electropolymerization step, has been fabricated for the determination of 2-Thioxanthine (2-TX). The extremely sensitive interlinked polymeric film formed at the surface of pyrolytic graphite was characterized by using Field Emission Scanning Electron Microscopy, Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Square Wave Voltammetry techniques. The sensing surface exhibited electrocatalytic effects towards the oxidation of 2-TX, by displaying the significant enhancement in the sensitivity in terms of an increase in the peak current and shift of the peak potential to less positive potentials. The proposed method exhibited linear relation of the peak current in the concentration range of 0.5–150μM and the limit of detection and limit of quantification were found as 1.0nM and 3.4nM, respectively. The developed approach has successfully been applied for the quantification of 2-TX in the presence of common interferents present in the urine.

Application of anodized edge-plane pyrolytic graphite electrode for analysis of clindamycin in pharmaceutical formulations and human urine samples

Different graphitic carbon-based electrode materials were evaluated for direct electro-oxidation of clindamycin and electroanalytical parameters such as sensitivity, residual background current, and signal-tobackground current ratio were compared to select the best one for the clindamycin electroanalysis. Such electrode materials include glassy carbon, carbon paste, pyrolytic graphite (edge-plane and basal-plane), carbon nanotube, reduced graphene oxide, and carbon black. The edge-plane pyrolytic graphite electrode after a simple and fast electrochemical pretreatment showed superior performance compared with the other carbon electrodes. Raman and Fourier transform infrared spectroscopy were employed to analyze the surface microstructure and chemical bonding of the carbon materials and scanning electron microscopy was used to study their surface morphologic features. The applicability of the electrochemically activated edge-plane pyrolytic graphite electrode for the determination of clindamycin in pharmaceutical formulations and human urine samples was evaluated.

A melamine based molecularly imprinted sensor for the determination of 8-hydroxydeoxyguanosine in human urine

A sensitive and facile molecular imprinted sensor has been fabricated using edge plane pyrolytic graphite (EPPG) for the determination of an important oxidative DNA damage product, 8-hydroxydeoxyguanosine (8-OHdG). The molecularly imprinted polymer film was fabricated by electropolymerization of melamine in the presence of 8-OHdG, on glutaraldehyde/poly 1,5-diaminonaphthalene modified EPPG. The imprinted sensor surface was characterized by using Field Emission Scanning Electron Microscopy, Electron Impedance Spectroscopy, Cyclic Voltammetry, Square Wave Voltammetry and UV–visible spectroscopy. The calibration response was linear over a concentration range of 20×10−9–3×10−6M of 8-OHdG with sensitivity and limit of detection (3σ/b) as 10.59µM/µA and 3×10−9M respectively. The common metabolites in urine, like uric acid, ascorbic acid, xanthine, hypoxanthine do not interfere up to 100-fold concentration. The imprinted sensor is also successfully employed for the determination of 8-OHdG in human urine sample of a renal failure patient.

Differential pulse voltammetric determination of an immunosuppressive drug teriflunomide on an edge plane pyrolytic graphite electrode

In the present work, sensitive and selective determination of teriflunomide (Trf) on an edge plane pyrolytic graphite electrode (EPPGE) using differential pulse voltammetry (DPV) is presented for the first time.

Melamine/Fe3O4 Nanoparticles Based Molecular Imprinted Highly Sensitive Sensor for Determination of Hydrochlorothiazide: An Antihypertensive Drug

A simple, facile and sensitive method for the fabrication of molecularly imprinted sensor is proposed for the determination of hydrochlorothiazide (HCTZ). The sensor is fabricated by the deposition of iron oxide nanoparticles followed by the electropolymerization of melamine monomer in the presence HCTZ at the surface of edge plane pyrolytic graphite. The surface of the imprinted sensor was characterized by using Field Emission Scanning Electron Microscopy, Energy dispersive X-ray analysis, Electrochemical Impedance Spectroscopy, X-ray diffraction, Cyclic Voltammetry and Square Wave Voltammetry. The oxidation of HCTZ occurred in a single, well-defined peak and the peak current was dependent on the concentration of HCTZ in the range 25 × 10−9–10 × 10−6 M. The sensitivity and limit of detection (3σ/b) were found to be 2.342 μM/μA and 4 nM respectively. The proposed method was applied for the determination of HCTZ in the presence of common metabolites present in human system. The obtained results indicated that uric acid, ascorbic acid, hypoxanthine and xanthine did not interfere up to 100 fold concentration. The imprinted sensor was successfully applied for determination of HCTZ in real samples such as pharmaceuticals and urine samples.

Application of Nanocrystalline Graphite‐like Pyrolytic Carbon Film Electrode in the Electroanalytical Determination of Famotidine

AbstractDirect electro‐oxidation of famotidine at different graphitic carbon‐based electrode materials was evaluated. These materials included conventional electrodes of edge‐plane pyrolytic graphite, basal‐plane pyrolytic graphite, carbon paste, and glassy carbon as well as nano‐structured carbon‐based materials such as pyrolytic carbon film, carbon nanotube, and nano‐graphene. Raman spectroscopy and scanning electron microscopy were employed to analyze their structural and morphological features. It was found that the pyrolytic carbon film electrode, after a simple and fast anodic activation, shows superior electroanalytical performance. The method was successfully applied for the electroanalytical determination of famotidine in tablet dosage forms and urine samples.

Carbon Material-Based Positive Electrodes for Aluminum Secondary Battery with a Chloroaluminate Ionic Liquid

Secondary batteries have already been utilized widely in various equipment, e.g., electric vehicle and cell-phone, but higher power density and capacity are required for supporting our modern life more than ever before. In order to achieve it, novel battery systems that are expected to take the place of conventional Li-ion battery (LIB) are proposed by a great number of research groups around the world. Above all, secondary battery using a multivalent-metal ion, e.g., Mg(II) and Al(III), has been expected to be a next generation battery because it can flow a larger current exceeding a conventional LIB. In a Lewis acidic haloaluminate ionic liquid (IL), it is well-known that aluminum can be electrochemically deposited with a high current efficiency. It suggests that the electrode reaction is a favorable one for constructing the Al secondary battery with the chloroaluminate IL. In fact, some remarkable researches on the Al secondary battery with haloaluminate ILs have been reported since the 1980.1-4 In this study, we have investigated the electrochemical behaviors of the various carbon positive electrodes in the Lewis acidic 60.0-40.0 mol % AlCl3–1-ethyl-3-methylimidazolium chloride (AlCl3–[C2mim]Cl) IL. The procedures used for the preparation and purification processes on the AlCl3−[C2mim]Cl IL were identical to those described in our articles. All the electrochemical experiments were conducted using a three-electrode beaker cell. A coiled Al wire was employed for the negative electrode. Five types of carbon materials were exploited to fabricate the positive electrode for an Al secondary battery. Those were an activated carbon fiber cloth covered with or without a graphene layer, a basal or an edge plane pyrolytic graphite, and a graphite-leaf powder. The reference electrode was an Al wire immersed in a neat 60.0-40.0 mol % AlCl3–[C2mim]Cl, if needed, but was separated from the bulk IL by porosity E glass frits. All experiments were carried out in an Ar gas-filled glove box with O2 and H2O < 1 ppm. Cyclic voltammograms recorded at different carbon positive electrodes in the 60.0 mol % AlCl3–[C2mim]Cl are shown in Fig. 1. At an activated carbon fiber cloth electrode, only an oxidation reaction appeared at the potential over ca. 2.25 V, and then electric double layer capacitance was also recognized due to the porous properties. But if the graphite (not shown) and graphene-coated electrodes were employed, several redox waves appeared. A small oxidation wave observed at ca. 1.70 V (vs. Al(III)/Al) should be the following electrochemical intercalation reaction. n C + [AlCl4]- ⇄ C n +[AlCl4]- + e- However, graphite electrodes, especially an edge plane pyrolytic one, were seriously damaged by the voltage sweep over 2.30 V. After the experiment, carbon powder precipitated in the IL electrolyte. In order to improve the behavior, graphite-leaf powder composite electrode was fabricated by using polymer binders that are stable in the IL. A typical voltammogram recorded at the electrode are shown in Fig. 1. Two clear oxidation waves appeared before increasing the oxidation current corresponding to the electrochemical oxidation of [AlCl4]-. It suggests that graphite intercalation compounds with different stages, e.g., stage 4, are produced during the anodic potential sweep.3 Based on the findings described above, we designed several Al secondary battery systems with different positive electrodes. Of these, use of the graphite-leaf powder composite electrode enabled high coulomb efficiency and discharge capacity up to 99 % and 80 mAh g-1, respectively, when the cut-off voltages were 0.80 and 2.10 V at the charge-discharge rate of the 50 mA g-1. The electrode performance strongly depended on the amount of the active material. This positive electrode will be one of the choices for designing the Al secondary battery. Acknowledgement Part of this research was supported by the Grant-in-Aid for Scientific Research, Grant Numbers 15H03591, 15K13287, and 15H2202 from the Japanese Ministry of Education, Culture, Sports, Science and Technology and by the ALCA-SPRING program, Japan Science and Technology Agency. References N. Takami and N. Koura, J. Electrochem. Soc., 140, 928 (1993).P. R. Gifford and J. B. Palmisano, J. Electrochem. Soc., 135, 650 (1988).M.-C. Lin, M. Gong, B. Lu, Y. Wu, D.-Y. Wang, M. Guan, M. Angell, C. Chen, J. Yang, B.-J. Hwang, and H. Dai, Nature, 520, 324 (2015).T. Tsuda, I. Kokubo, M. Kawabata, M. Yamagata, M. Ishikawa, S. Kusumoto, A. Imanishi, and S. Kuwabata, J. Electrochem. Soc., 161, A908 (2014). Figure 1

A Novel Hybrid Nano‐composite Grafted Electrochemically Reduced Graphene Oxide Based Sensor for Sensitive Determination of Efavirenz

AbstractA novel, facile fabrication, based on electrochemically reduced graphene oxide (ErGO), grafted with Pt nanoparticles and Nafion hybrid nano‐composite (ErGO‐Pt/Nafion) on the surface of edge plane pyrolytic graphite (EPPG) has been reported. The fabricated sensor has been used for the sensitive and selective determination of efavirenz (EFZ), a well‐known drug for HIV infections. The ErGO‐Pt/Nafion film was characterized by Field Emission Scanning Electron Microscopy (FE‐SEM), Energy‐dispersive X‐ray spectrometry (EDS) and Electrochemical Impedance Spectroscopy (EIS). The experimental results reveal that the modified sensor displays an excellent electrocatalytic activity towards the oxidation of EFZ and exhibits a large linear dynamic relationship in the range of 0.05 μM to 150 μM, with a detection limit of 1.8 nM. Practical utility of the developed sensor has been demonstrated by determining the EFZ in biological fluids and pharmaceutical samples and a low detection limit with high sensitivity observed makes it valuable for the clinical diagnosis.

Electrochemical Red Blood Cell Counting: One at a Time

We demonstrate that the concentration of a red blood cell solution under physiological conditions can be determined by electrochemical voltammetry. The magnitude of the oxygen reduction currents produced at an edge-plane pyrolytic graphite electrode was diagnosed analytically at concentrations suitable for a point-of-care test device. The currents could be further enhanced when the solution of red blood cells was exposed to hydrogen peroxide. We show that the enhanced signal can be used to detect red blood cells at a single entity level. The method presented relies on the catalytic activity of red blood cells towards hydrogen peroxide and on surface-induced haemolysis. Each single cell activity is expressed as current spikes decaying within a few seconds back to the background current. The frequency of such current spikes is proportional to the concentration of cells in solution.

Direct electrochemistry of nitrate reductase from the fungus Neurospora crassa

We report the first direct (unmediated) catalytic electrochemistry of a eukaryotic nitrate reductase (NR). NR from the filamentous fungus Neurospora crassa, is a member of the mononuclear molybdenum enzyme family and contains a Mo, heme and FAD cofactor which are involved in electron transfer from NAD(P)H to the (Mo) active site where reduction of nitrate to nitrite takes place. NR was adsorbed on an edge plane pyrolytic graphite (EPG) working electrode. Non-turnover redox responses were observed in the absence of nitrate from holo NR and three variants lacking the FAD, heme or Mo cofactor. The FAD response is due to dissociated cofactor in all cases. In the presence of nitrate, NR shows a pronounced cathodic catalytic wave with an apparent Michaelis constant (KM) of 39μM (pH7). The catalytic cathodic current increases with temperature from 5 to 35°C and an activation enthalpy of 26kJmol−1 was determined. In spite of dissociation of the FAD cofactor, catalytically activity is maintained.

Anodized Edge-plane pyrolytic graphite for electroanalysis of pantoprazole in tablet dosage forms and human urine samples

Electroanalytical parameters of different graphitic carbon-based electrode materials were compared to select the best one for the pantoprazole electroanalysis. Such parameters include sensitivity, repeatability, residual background current, and signal-to background current ratio of the analytical response and such electrodes include conventional carbon-based electrodes such as glassy carbon (GC), carbon paste, edge-plane pyrolytic graphite (EPPG), and basal-plane pyrolytic graphite electrodes and film-coated modified GC electrodes with graphitic carbon-based materials such as carbon nanotube, nanographene, carbon black and graphite powder. The EPPG electrode, after applying a simple electrochemical anodization, showed more acceptable analytical performances compared with the other electrodes. Raman spectroscopy was employed to study the surface structural changes that occurred dring the anodic activation. Calibration plot with a good linearity was obtained in the concentration range of 0.2-25 and 0.02-8.5 µM, and the detection limit was estimated to be 0.055 and 0.0041µM using cyclic voltammetry and differential pulse voltammetry techniques, respectively. Finally, the electrochemically activated EPPG electrode was used successfully for the determination of pantoprazole in tablet dosage forms and human urine samples with satisfactory results.

Poly-Melamine Film Modified Sensor for the Sensitive and Selective Determination of Propranolol, a β-blocker in Biological Fluids

The study reports synthesis of poly-(melamine) film on the surface of edge plane pyrolytic graphite (EPPG) followed by its characterization using cyclic voltammetry, square wave voltammetry, field emission scanning electron microscopy (FE-SEM), Horizontal Attenuated Total Reflectance-infrared spectroscopy (HATR-IR) and electrochemical impedance spectroscopy (EIS). The p-(melamine) film coated EPPG has been used as a highly sensitive electrochemical sensor for the determination of propranolol, a β-blocker. The p-(melamine)/EPPG sensor showed excellent electrocatalytic activity for the oxidation of propranolol by significant increment in the peak current and shift in the peak potential toward less positive potential. The fabricated sensor exhibited linear increase in the oxidation peak current with the increasing propranolol concentration in the range 0.1–800 μM with the L.O.D. and L.O.Q. as 9 nM and 30 nM, respectively. The effect of interferents on the peak current response has been studied and it is observed that the common metabolites present in the biological fluid matrix did not interfere in the determination. The p-(melamine)/ EPPG sensor displayed advantages such as simple preparation, high sensitivity, excellent selectivity and good reproducibility toward determination of propranolol. To ensure the analytical applicability of the fabricated sensor, the method has been successfully demonstrated by determining propranolol in the commercial pharmaceutical formulations, human urine and plasma samples.

Glass-like carbon, pyrolytic graphite or nanostructured carbon for electrochemical sensing of bismuth ion?

Different carbon electrodes were explored for application in electroanalysis, namely for sensing of bismuth ion as model analyte. Carbon materials tested included glassy carbon, basal and edge plane pyrolytic graphite, as well as nanostructured carbonized polyaniline prepared in the presence of 3,5-dinitrosalicylic acid. Bismuth ion was chosen as model analyte as protocol for its detection and quantifications is still to be determined. Herein, anodic stripping voltammetry was used with study of effect of several parameters such as scan rate and deposition time. Electrode based on carbonized polyaniline showed the highest activity for bismuth ion sensing in terms of the highest current densities recorded both in a laboratory and in real sample, while basal plane pyrolytic graphite electrode gave the lowest limit of detection.

Electrochemical investigations of 8-hydroxydeoxyguanosine and its determination at an edge plane pyrolytic graphite electrode

Electrochemical oxidation of 8-hydroxydeoxyguanosine (8-OHdG) and its detection with low detection limit is reported at pyrolytic graphite electrode.