Glassy Carbon Disk Research Articles

Characterization of metal cations-complexing polymer films interactions followed with anodic stripping voltammetry

The complexing ability of thin poly(3-pyrrol-1-ylpropyl)malonic acid films coated onto glassy carbon disc electrode surfaces was evaluated towards Pb(II) and Cu(II) ions, using the chemical preconcentration-anodic stripping method. The affinity of these metal cations for the complexing film modified electrodes and their maximal surface coverage rate could be evaluated from a Langmuir isotherm model coupled to the chemical preconcentration-anodic stripping technique. Isothermal studies conducted between 293 and 308 K allowed to estimate enthalpy and entropy variations associated to the metal sorption, which expectedly proved to fit chemisorption processes. As judged from the estimated binding constants, Pb(II) ions turned out to present a higher affinity for the functionalized surface than the smaller Cu(II) species. The mobilization of a higher number of malonic acid units per metal cation upon complexation of Pb(II), as compared to Cu(II), is however believed to account for the estimated lower Pb(II) surface coverage. The combination of the Langmuir isotherm model to the chemical preconcentration-anodic stripping technique is thus revealed to be an efficient method to characterize the complexing ability of complexing film electrode surface.

Experimental and Theoretical Study of Cobalt Selenide as a Catalyst for O2Electroreduction

Cobalt sulfides have been known for more than 30 years to be active toward oxygen reduction, and cobalt selenides have shown less activity. In this paper, a theoretical analysis is made of the four-electron reduction reaction of oxygen to water over the mixed anion and cation (202) surface of the pentlandite structure Co9Se8, one of several selenide phases. Reversible potentials for forming adsorbed reaction intermediates in acid are predicted using adsorption energies calculated with the Vienna ab initio simulation program (VASP) and the known bulk solution values together in a linear Gibbs energy relationship. Comparison with an earlier theoretical analysis of pentlandite structure Co9S8 shows that the overpotential is predicted to be larger for the selenide by around 0.22 V. Cobalt selenide electrodes of unspecified stoichiometry were prepared chemically on glassy carbon discs, and polarization curves were measured using rotating discs. When heat-treated at 900 °C, the onset potential for O2 reduction was found to be 0.5 V (normal hydrogen electrode, NHE), whereas electrodes not subject to heat-treatment were inactive. For Co3S4, onset potentials in the literature are ∼0.8 V (NHE), consistent with a ∼0.3 V higher measured overpotential for the selenide. The theoretical predictions for the pentlandite sulfide and selenide surfaces are in qualitative agreement.

Electroanalytical Characterization of Verapamil and its Voltammetric Determination in Pharmaceuticals and Human Serum

The electrooxidative behavior and determination of Verapamil HCl, one of the class IV anti‐arrhythmic agent, on a glassy carbon disc electrode were investigated for the first time by using cyclic, differential pulse (DPV), and Osteryoung square wave voltammetry (OSWV). Verapamil showed an irreversible oxidation behavior at all pH values and buffers studied. From the electrochemical response, the main oxidation step was found to be related to the methoxy group on the phenyl ring. DPV and OSWV were used to generate peak current versus concentration curves for verapamil. A linear response was obtained in the range comprised between 8×10−7 and 1×10−4 M for both techniques with detection limit of 1.61×10−7 M for DPV and 1.33×10−7 M for OSWV. The repeatability and reproducibility of the methods for all investigated media (such as supporting electrolyte and serum samples) were determined. Precision and accuracy were also checked in all media. The methods were proposed for the determination of verapamil in dosage forms adopting both DPV and OSWV modes. The methods were extended to the in vitro determination of verapamil in spiked serum samples. No electroactive interferences from the endogenous substances were found in human plasma.

Simultaneous voltammetric detection of dopamine and uric acid at their physiological level in the presence of ascorbic acid using poly(acrylic acid)-multiwalled carbon-nanotube composite-covered glassy-carbon electrode

The use of poly(acrylic acid) (PAA)-multiwalled carbon-nanotubes (MWNTs) composite-coated glassy-carbon disk electrode (GCE) (PAA-MWNTs/GCE) for the simultaneous determination of physiological level dopamine (DA) and uric acid (UA) in the presence of an excess of ascorbic acid (AA) in a pH 7.4 phosphate-buffered solution was proposed. PAA-MWNTs composite was prepared by mixing of MWNTs powder into 1 mg/ml PAA aqueous solution under sonication. GCE surface was modified with PAA-MWNTs film by casting. AA demonstrates no voltammetric peak at PAA-MWNTs/GCE. The PAA-MWNTs composite is of a high surface area and of affinity for DA and UA adsorption. DA exhibits greatly improved electron-transfer rate and is electro-catalyzed at PAA-MWNTs/GCE. Moreover, the electro-catalytic oxidation of UA at PAA-MWNTs/GCE is observed, which makes it possible to detect lower level UA. Therefore, the enhanced electrocatalytic currents for DA and UA were observed. The anodic peak currents at ∼0.18 V and 0.35 V increase with the increasing concentrations of DA and UA, respectively, which correspond to the voltammetric peaks of DA and UA, respectively. The linear ranges are 40 nM to 3 μM DA and 0.3 μM to 10 μM UA in the presence of 0.3 mM AA. The lowest detection limits (S/N = 3) were 20 nM DA and 110 nM UA.

Attachment of anthraquinone derivatives to glassy carbon and the electrocatalytic behavior of the modified electrodes toward oxygen reduction

The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with anthraquinones was studied using cyclic voltammetry (CV) and the rotating disk electrode (RDE) technique. Two methods were used in surface modification. The first method comprised immersion of the polished or anodically pretreated GC electrode in a solution containing 9,10-anthraquinone-2-carboxylic acid (AQ-2-COOH) or its anion (AQ-2-COO−) in dimethylsulfoxide (DMSO) or 9,10-anthraquinone-2-ethanoic acid (AQ-2-CH2COOH) or its anion (AQ-2-CH2COO−) in N,N-dimethylformamide (DMF). Alternatively, the surface of the GC disk was modified by anodic oxidation of AQ-2-COOH or AQ-2-COO− in DMSO or AQ-2-CH2COOH in DMSO or DMF or AQ-2-CH2COO− in DMF. The modified electrodes showed electrocatalytic activity toward oxygen reduction in 0.1 M acetate buffer pH (4.8), 0.1 M phosphate buffer (pH 8) and 0.1 M NaOH. Atomic force microscopy (AFM) examination of the modified electrodes was carried out and the differences in surface morphology of various modifications were in evidence.

CuxCo3 − xO4 Used as Bifunctional Electrocatalyst: II. Electrochemical Characterization for the Oxygen Reduction Reaction

Composite film electrodes containing mechanically mixed or particles, carbon-black Vulcan XC-72R, and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) were formed on the glassy carbon disk surface of a rotating ring-disk electrode (RRDE) and studied for the oxygen reduction reaction (ORR) in -saturated solution. The highest current densities were observed with and they increased with the oxide content in the film, hence clearly demonstrating the excellent intrinsic electrocatalytic activity of for this reaction. The results also showed that is a better electrocatalyst than with higher current densities and a greater number of electrons exchanged per molecule. It was found that the copper–cobalt spinel oxide component favors a total of in the oxygen reduction process. At the -based composite electrode, direct reduction of into ions (rate constant ) and the peroxide pathway (formation of ions and their reduction into ions, rate constants and ) are proceeding in parallel, with a ratio that increases with the overpotential when the oxide content is greater than 23.5%. At the -based composite electrode, is very weak with a ratio that decreases rapidly with the overpotential.

The Global and Local Impedance Response of a Blocking Disk Electrode with Local Constant-Phase-Element Behavior

Numerical methods were used to calculate the influence of geometry-induced current and potential distributions on the impedance response of a blocking disk electrode with a local constant-phase element behavior. While the calculated global impedance is purely capacitive, the local impedance has high-frequency inductive loops that were observed in experiments conducted on a stainless steel electrode in electrolyte. The calculated global impedance responses are in good agreement with experimental results obtained using both the steel electrode and a glassy-carbon disk in electrolytes of differing concentrations. The computed local and both local and global ohmic impedances are shown to provide insight into the frequency dispersion associated with the geometry of disk electrodes.

Catalytic Reduction of 4 , 4 ′ -(2,2,2-Trichloroethane-1,1-diyl)bis(chlorobenzene) with Cobalt(I) Salen Electrogenerated at Vitreous Carbon Cathodes in Dimethylformamide

Cyclic voltammetry (CV) and controlled-potential electrolysis have been utilized to investigate the catalytic reduction of -(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) by cobalt(I) salen electrochemically generated at a carbon cathode in dimethylformamide containing tetramethylammonium tetrafluoroborate. As a prelude to this study, CV has revealed that direct reduction of DDT at a glassy carbon disk electrode shows six peaks; the process associated with each peak has been assigned on the basis of an examination of the electrochemistry of various reduced forms of DDT. CVs for the reduction of cobalt(II) salen in the presence of DDT exhibit the classic characteristics of a catalytic process, including an enhanced cathodic current for the cobalt(II) salen–cobalt(I) salen redox couple and a disappearance of the anodic peak for oxidation of cobalt(I) salen. Bulk electrolysis of solutions containing cobalt(II) salen and DDT at a reticulated vitreous carbon cathode results in the formation of a mixture of products—-(2-chloroethene-1,1-diyl)bis(chlorobenzene), -(ethene-1,1-diyl)bis(chlorobenzene) (DDNU), 1-chloro-4-(2-chloro-1-phenylvinyl)benzene (an isomer of DDNU), -(2,2-dichloroethene-1,1-diyl)bis(chlorobenzene), and -(2,2-dichloroethane-1,1-diyl)bis(chlorobenzene). A mechanistic scheme is proposed to account for the formation of products.

Electrochemical Grafting of an Aryl Fluorosulfonimide Electrolyte onto Glassy Carbon

Robust bonded layers of an aromatic fluorosulfonimide electrolyte were created on glassy carbon disk and plate electrodes by electroreduction of a new fluorosulfonimide aryl diazonium zwitterion. Formation of the bonded layer was confirmed by XPS of the modified surfaces and also by the effect of the bound layer on reduction/oxidation of redox-active probe molecules. Surface coverage in the monolayer range was achieved. Counterions for as-formed layers were initially tetra-alkylammonium ions from the coating electrolyte but could subsequently be exchanged for other cations by exposure to salt solutions. The bonded layers are very stable with respect to treatment with solvents (water and/or acetonitrile), dry heat (120 degrees C), and hot acid (triflic acid, 80 degrees C, neat and containing 50 wt % water); however, they are unstable with respect to electro-oxidative scanning in aqueous electrolyte solutions.

CuxCo3 − xO4 Used as Bifunctional Electrocatalyst: Physicochemical properties and electrochemical characterization for the oxygen evolution reaction

( and 1) powders were prepared by a sol-gel method which favors high oxide specific surface areas with a larger value for , ascribed to a larger powder mesopore volume. X-ray diffraction measurements reveal that particles are less crystalline than with crystallite size 10 times smaller. The sol-gel method allows formation of spinel oxide particles that do not contain any resistive CuO phase. X-ray photoelectron spectroscopy analyses have shown that contains and species at the surface, tetrahedral cations being predominant. In the case of , , , and possibly cations are also detected, octahedral showing the highest concentration among the copper species. Composite film electrodes, based on mechanically mixed or particles, carbon black Vulcan XC-72R, and poly(vinylidene fluoride-co-hexafluoropropylene), were formed on a glassy carbon disk surface. The highest intrinsic electrocatalytic activity for the oxygen evolution reaction is obtained for the composite electrode containing the larger amount of oxide particles. Cyclic voltammetry experiments suggest that the surface ratio is decreased when the electrodes are immersed into the KOH electrolyte, which may be associated to the formation of a superficial CoOOH layer.

Electrooxidation of dissolved dsDNA backed by in situ UV–Vis spectroscopy

The electrooxidation of double-stranded DNA (dsDNA) from calf thymus was carried by using cyclic voltammetry. A glassy carbon disk-, a platinum disk-, a platinum mesh- and a carbon vapor-deposited platinum mesh electrodes were used. It is shown that the appropriate chemical and biological (steam treatment) purification of the complete cell allows, for the graphite electrode, formation of a wide anodic dsDNA signal with two visible anodic peaks. There was no necessity of preaccumulation of dsDNA on the electrode surface and of use of mediators to get well defined voltammetric signals. These peaks apparently reflect electrooxidation of the DNA's guanine and adenine. The spectrophotometric data obtained during the electrooxidation indicate that the absorbance increases with an increase in potential and electrooxidation current of dsDNA. However, the absorption band maximum either does or does not change its position depending on the mesh material. This different spectroscopic behavior may mean that the changes in the dsDNA structure upon electrooxidation are different in the case of Pt and C electrodes.

Microscopic Studies of the GC/Poly-NiTMHPP/Nafion Electrochemical Nitric Oxide Sensor

Glassy carbon (GC) discs and platinum microcylindrical electrodes were modified with a layer of nickel(II) tetrakis 3-methoxy-4 hydroxyphenyl porphyrin (poly-TMHPP-Ni) of different loadings (Γ) between 0.6 and 10 nmol/cm2, and subsequently with a Nafion layer. The topography and in some cases the thickness of films were measured by means of contact mode AFM. SEM and optical microscopy observations were used for the comparative studies on a larger scale. The useful range of the coverage with modifying polymer was investigated. The optimal value of loading for the sensor was found to be in the range of 6-8 nmole of poly-TMHPP-Ni per cm2. We observed the Nafion layer uniformity in nanometric scale.

Nanoscale Topography of GC/Pt-C and GC/Pt-Ru-C Electrodes Studied by Means of STM, AFM and XRD Methods

Electrodes, assigned as GC/Pt-C and GC/Pt-Ru-C, were formed by deposition of Ptbased catalysts (47.5 wt % Pt + high surface area carbon) and (54 wt. % Pt-Ru alloy + high surface area carbon) on glassy carbon (GC) discs. X-ray diffraction measurements were used for the determination of the average crystallite size and phase composition of both catalysts. Crystallite size for Pt-C catalyst was 2.9 nm for Pt-fcc. In the diffraction pattern of the Pt-Ru-C catalyst two phases, e.g. Pt-Ru-fcc and Ru-hcp were refined using the Rietveld method. Crystallite sizes were 3.9 nm for Pt-Ru-fcc and 2.8 nm for Ru-hcp. STM observations of the surface of GC/Pt-C and GC/Pt-Ru-C electrodes revealed the presence of metal particles of the size in the range 2-6 nm and Pt-C or Pt- Ru-C agglomerates in the range of several tenth of nm. The thickness of the Nafion covering layer determined by AFM is ca. 100 nm. A simplified scheme of the investigated electrodes was created.

An experimental system for evaluation of well-defined catalysts on nonporous electrodes in realistic DMFC environment

This paper reports on an experimental setup wich enables us to investigate planar model catalysts in an environment closely resembling the environment found in an actual direct methanol fuel cell. The working electrodes were nano-structured catalyst particles immobilised on planar supports, reducing many of the commonly present non-catalyst related effects in conventional porous electrodes. Colloidal lithography was used for nano-structuring the samples. Nafion was used as electrolyte. Results are presented for the oxidation of methanol, formaldehyde, formic acid and carbon monoxide at temperatures between 30 and 70 ° C on Pt particles supported on glassy carbon disks.

Hydrogen Peroxide Formation as a Degradation Factor of Polymer Electrolyte Fuel Cells

20wt.% Pt/C catalyst was loaded at different densities (0.28- 56.7 mgcarbon cm-2) on glassy carbon (GC) disk electrode, and the effect of its agglomeration on hydrogen peroxide formation in oxygen reduction reaction (ORR) was investigated by the rotating ring-disk electrode technique. The formation of H2O2 was enhanced with a reduction in agglomeration of Pt/C. Even in the operating potential range of PEFC cathodes (0.6-0.8 V), 20% of hydrogen peroxide was formed on Pt/C loaded at densities lower than 1.41 mgcarbon cm-2 on GC. These results revealed that series 2-electron reduction pathway, which is negligible on clean bulk Pt surface, exists on Pt nanoparticles supported on carbon. A large amount of H2O2 formation was observed on Pt nanoparticles deposited not only on GC, but also on Au, which indicated that H2O2 formation is not specific to Pt nanoparticles on carbon support.

Influence of nature, concentration and pH of buffer acid–base system on rate determining step of the electrochemiluminescence of Ru(bpy) 32+ with tertiary aliphatic amines

The electrogenerated chemiluminescence (ECL) of Ru(bpy) 3 2+ (bpy = 2,2′-bipyridyl) with tertiary aliphatic amines as co-reactants, was theoretically and experimentally studied as a function of the pre-equilibria involved in the ammonium proton lost and in relation to the nature of the rate determining step. Transient potential steps were used with a 3-mm glassy carbon disk electrode or carbon fiber ultramicroelectrodes array to investigate emission behavior in a variety of aqueous solution types, containing phosphate, tartrate and phthalate acid–base systems at differing pH values. The emission of Ru(bpy) 3 2+ resulting from the reaction with n-tripropylamine (TPrA), tri-isobutylamine (TisoBuA), n-tributylamine (TBuA), methyl-di- n-propylamine (MeDPrA) and triethylamine (TEtA) in varying acid–base media was interpreted on the basis of the quoted pre-equilibria, ammonium p K a being known. The nature of the rate determining steps changes depending on pH. Above pH ≈ 5 the amine neutral radical formation is the rate determining step and, is independent of pH with rate constant close to 10 3 s −1; below pH ≈ 5 the rate determining step becomes the deprotonation of the ammonium ion, operated by different bases present in solution. Different amines in the same acid–base system showed analogous ECL behavior, conditioned by the chosen acid base system. A single amine in different acid–base systems showed different kinetic behaviors, due to the dissociation constants of the chosen buffers. The concentration of the acid–base system also played an important role and influenced emission intensity and shape. ECL emission were simulated by finite difference methods, implementing a previously proposed mechanism by including the relevant pre-equilibria. Simulation may also give estimates of the p K a values of the ammonium ions. An ion pair formation between R 3N + and the mostly charged species present in solution is hypothesized to explain the contradictory experimental results concerning the reaction mechanism of the proton lost of the radical cation.

Determination of Mercury by Chronopotentiometric Stripping Analysis Using Glassy Carbon Vessel as a Working Electrode

AbstractIn this work chronopotentiometric stripping analysis of mercury was performed using a process vessel of glassy carbon as a working electrode. Experimental parameters for both steady and rotating vessel were investigated and compared. Relative sensitivity as well as the sharpness of the analytical signal was better when the rotation of the process vessel was performed. The new design provided better sensitivity when compared to both stationary and rotating glassy carbon disk electrodes. Detection limit obtained for the electrolysis time of 600 s was 0.1 ng/L of Hg(II). The accuracy of the technique was confirmed by analyzing the standard reference material – tomato leaves.

Tris(2,2′-bipyridyl)ruthenium(II)–Zirconia–Nafion composite modified electrode applied as solid-state electrochemiluminescence detector on electrophoretic microchip for detection of pharmaceuticals of tramadol, lidocaine and ofloxacin

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+)–Zirconia–Nafion composite modified glassy carbon disk electrode as a solid-state electrochemiluminescence (ECL) detector is successfully applied to an electrophoretic microchip system with a wall-jet configuration. Pharmaceuticals such as tramadol, lidocaine and ofloxacin were selected to characterize the performance of this microchip capillary electrophoresis (CE)–ECL detection system. Voltammetric and ECL behaviors of immobilized Ru(bpy) 3 2+ were investigated in lidocaine system. Influences of the separation electric field to cyclic voltammograms (CVs) of the immobilized Ru(bpy) 3 2+ were also investigated. Tramadol, lidocaine and ofloxacin can be baseline separated without any additives. The detection limits (S/N = 3) were 2.5 × 10 −5 mol L −1 for tramadol, 5.0 × 10 −6 mol L −1 for lidocaine, 1.0 × 10 −5 mol L −1 for ofloxacin under the sample injection of picoliters, and the linear ranges were from 5.0 × 10 −5 to 2.5 × 10 −3 mol L −1 for tramadol, 1.0 × 10 −5 to 1.0 × 10 −3 mol L −1 for lidocaine, and 1.0 × 10 −5 to 2.5 × 10 −3 mol L −1 for ofloxacin, respectively.

Electrocatalytic oxidation of methanol on a Nickel(II)-1-(2-pyridylazo)-2-naphthol complex modified glassy-carbon electrode in alkaline medium

Electrocatalytic oxidation of methanol on a glassy carbon disc electrode modified with Ni(II)-1-(2-pyridylazo)-2-naphthol (Ni-PAN) complex and conditioned by potential recycling in a limited range (between 100–600 mV) in 0.1 M NaOH solution, abbreviated as NiPANME, is studied by cyclic voltammetry in alkaline medium. The results are compared with those obtained for a NiO modified glassy-carbon electrode, NiOME, prepared in similar conditions. The findings show that the NiPAN film behaves as an efficient electrocatalyst for the oxidation of methanol in alkaline medium via Ni(III) species with the cross-exchange reaction occurring throughout the layer at a low concentration of methanol and for a thin film of modifier. Effects of the scan rate and methanol concentration on the methanol oxidation are investigated. The cyclic voltammetry and amperometry methods are used to investigate the methanol electrooxidation at the modified electrode.

Influence of ligand structures on methanol electro-oxidation by mixed catalysts based on platinum and organic metal complexes for DMFC

In order to investigate the influence of mixing organic metal complexes with various metal coordination structure on Pt/C catalyst for methanol oxidation reaction (MOR) in acidic media, N, N′-mono-8-quinolyl- o-phenylenediamine (mqph), N, N′-bis(anthranilidene)ethylenediamine (anthen) and N, N′-bis(salicylidene)ethylenediamine (salen), coordinating to Co(II) and Ni(II), were examined as the model compounds. M(mqph), M(anthen) and M(salen) have MN 3, MN 4 and MN 2O 2 moiety as the catalytic active sites, respectively. Pt–M(complex)/C mixed catalysts were prepared by depositing the mixture of Pt tetra-ammine chloride and each organic metal complex with various mixing ratio (w/o) on graphite powder and then heat-treating at 600 °C in Ar atmosphere. The Pt–M(complex)/C samples were put on a glassy carbon disk electrode, and tested for electrochemical MOR in 1 mol dm −3 CH 3OH + 0.05 mol dm −3 H 2SO 4 aqueous solutions at 25 °C. The mixed catalysts, especially Pt–Ni(mqph)/C and Pt–Co(mqph)/C, were found to enhance the MOR and exhibited higher catalytic activities than Pt/C, although each organic metal complex solely showed no catalytic activity. The catalytic ability was enhanced by mixing up to 50/50 (Pt–M(complex)) mixing ratio for the Co(mqph) and up to 80/20 mixing ratio for the Ni(mqph). Larger amounts of M(complex) resulted in a decrease in the catalytic activities. These results indicate that the organic metal complexes, especially M(mqph), promote effectively the electrochemical MOR on Pt/C catalyst, the degree of which depends strongly on the ligand structure. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectra (XAS) for the Pt–M(complex)/C mixed catalysts showed that the metal coordination structures of organic metal complexes are partially retained on the graphite powder even after the severe heat-treatment at 600 °C in Ar atmosphere. Ab initio calculations for the organic metal complexes exhibited that the Ni metal site of the Ni(mqph) interact with OH − group more strongly than those of the other organic metal complexes. This fact suggests that the Pt–M(mqph)/C electro-oxidizes a byproduct CO absorbed on Pt by “bifunctional effect” in a similar way as Pt–Ru alloy catalysts do in promoting the effective electrochemical MOR.