Glassy Carbon Rotating Disk Electrode Research Articles

A Fe3O4-Based Chemical Sensor for Cathodic Determination of Hydrogen Peroxide

A new cathodic scheme for hydrogen peroxide (H2O2) measurement by Fe3O4-based chemical sensor was described. The unique characteristic of electrocatalytic property was firstly investigated by voltammetry. And then the amperometric response of H2O2 was measured at −0.2 V (vs. Ag/AgCl) by Fe3O4 modified glassy carbon rotating disk electrode. The kinetic parameter was also calculated from Koutecky-Levich plot, and the value was 6.4×10−4 cm s−1 in pH 3 citrate buffer. In order to benefit the possible biomedical applications, Fe3O4/chitosan modified electrode was also investigated in this experiment. There were several characteristic enhancements by the coated chitosan thin film for H2O2 sensor. The calibration curves were found to be linear up to 4.0 and 5.0 mM (r=0.999) in pH 3 and 7 with the detection limits of 7.6 and 7.4 μM L−1 (S/N=3). The stability was evaluated by the results of half-life time (t50%) for 9 months at room temperature and 24 months at 4 °C.

Study of electrochemical oxidation and determination of albendazole using a glassy carbon-rotating disk electrode

In this work, electrochemical oxidation of albendazole (ABZ) was carried out using a glassy carbon-rotating disk electrode. Development of electroanalytical methodology for ABZ quantification in pharmaceutical formulations was also proposed by using linear sweep voltammetric technique. Electrochemical oxidation is observed for ABZ at E 1/2 = 0.99 V vs. Ag/AgCl sat, when an anodic wave is observed. Kinetic parameters obtained for ABZ oxidation exhibited a standard heterogeneous rate constant for the electrodic process equal to (1.51 ± 0.07) × 10 –5 cm s –1, with a αn a value equal to 0.76. Limiting current dependence against ABZ concentration exhibited linearity on 5.0 × 10 –5 to 1.0 × 10 –2 mol l –1 range, being obtained a detection limit of 2.4 × 10 –5 mol l –1. Proposed methodology was applied to ABZ quantification in pharmaceutical formulations.

Thermodynamic Guidelines for the Design of Bimetallic Catalysts for Oxygen Electroreduction and Rapid Screening by Scanning Electrochemical Microscopy. M−Co (M: Pd, Ag, Au)

We propose guidelines for the design of improved bimetallic (and related) electrocatalysts for the oxygen reduction reaction (ORR) in acidic media. This guide is based on simple thermodynamic principles assuming a simple mechanism where one metal breaks the oxygen-oxygen bond of molecular O(2) and the other metal acts to reduce the resulting adsorbed atomic oxygen. Analysis of the Gibbs free energies of these two reactions guides the selection of combinations of metals that can produce alloy surfaces with enhanced activity for the ORR when compared to the constituent metals. Selected systems have been tested by fabricating arrays of metallic catalysts consisting of various binary and ternary combinations of Pd, Au, Ag, and Co deposited on glassy carbon (GC) substrates. The electrocatalytic activity of these materials for the ORR in acidic medium was examined using scanning electrochemical microscopy (SECM) in a new rapid-imaging mode. This was used to rapidly screen arrays covering a wide range of catalyst compositions for their activity for the ORR in 0.5 M H(2)SO(4). Using the SECM technique, we have identified combinations of metals with enhanced electrocatalytic activities when compared with the constituent, pure metals. Addition of Co to Pd, Au, and Ag clearly decreases the ORR overpotential, in agreement with the proposed model. Catalyst spots that exhibited enhanced electrocatalytic activity in the SECM screening technique were then examined using classical rotating disk electrode (RDE) experiments. The activity of carbon black supported catalyst mixtures on a GC RDE and the electrocatalytic activity determined using the SECM screening technique showed excellent agreement. C/Pd-Co electrodes (10-30% Co) exhibited remarkable activity for ORR catalysis, close to that of carbon-supported Pt.

Electrochemical deposition of PtRu on an uncatalyzed carbon electrode for methanol electrooxidation

This research aims to increase the utilization of platinum–ruthenium alloy (PtRu) catalysts and thus to lower the catalyst loadings in the electrode for methanol electrooxidation. The electrodeposition of PtRu was performed on a rotating disk electrode (RDE) of glassy carbon (GC), on which a layer of Nafion ®-bonded carbon (Vulcan XC 72R) was dispersed in advance. First, the behavior of Pt RDE and GC RDE in an aqueous solution containing HCl, H 2PtCl 6 and RuCl 3 was studied. It was found that the hydrogen evolution becomes a dominant reaction when the electrode potential is below −0.20 V vs. SSCE (saturated-potassium–chloride silver chloride electrode). The hydrogen evolution was strongly enhanced with the formation of nanometer-sized Pt particles on the RDE. To enrich Pt and Ru ions, present in the form of anionic complexes in solution, onto the carbon particles in the uncatalyzed carbon electrode (UCE) and, most importantly, to eliminate the hydrogen bubbles formed on the UCE during the cathodic deposition, a positive current was imposed on the UCE for a period of time prior to each step of cathodic deposition of PtRu, should multiple steps of cathodic deposition be required. Cyclic voltammograms (CVs) of electrodes in 0.5 M H 2SO 4 before and after deposition were used to evaluate the loading of metal catalysts based upon the profile of CV in a wide range of potentials from −0.20 to 1.1 V vs. SSCE. The catalytic activity of electrodes prepared under different conditions for methanol electrooxidation was studied by electrochemical methods. The results showed that the performance of the electrode (prepared in this study) with loadings estimated to 77 μg PtRu/cm 2 is much better than that of a conventional electrode with loadings of 100 μg Pt/cm 2. The role of ruthenium in methanol oxidation was also discussed in electrochemical terms.

Kinetic Characterization of PtRu Fuel Cell Anode Catalysts Made by Spontaneous Pt Deposition on Ru Nanoparticles

Hydrogen oxidation kinetics without and with trace amounts of CO in were investigated for carbon-supported catalysts consisting of Pt submonolayers on Ru nanoparticles prepared by spontaneous deposition and commercial Pt, Ru, and PtRu alloy catalysts. Thin catalyst layers were deposited onto a glassy carbon rotating disk electrode without using Nafion film to stabilize them. Nonlinear fittings of the entire polarization curves at several rotation rates were used to determine the exchange current, the Tafel slope, and the Levich slope. To ensure full utilization of the catalyst, the mass-specific activity was determined by finding the minimum Pt loading needed to have all three kinetic parameters close to those found for a polycrystalline Pt electrode. For the and samples prepared by spontaneous deposition of 1/9 to 4/9 monolayer Pt on Ru, the minimum loading is This is only one-third of that for Pt or PtRu (E-TEK) catalysts and only double the atomic density of a Pt(111) surface, indicating that the high activity of Pt metal for hydrogen oxidation is retained when the atomic assemblies are reduced to submonolayer level on Ru. The enhanced CO tolerance was studied at low potentials by correlating the loss of the activity in 0.1% with the CO coverage on Pt and Ru sites. © 2003 The Electrochemical Society. All rights reserved.

Electrochemical characterization of unsupported high area platinum dispersed on the surface of a glassy carbon rotating disk electrode in the absence of Nafion® or other additives

A method is described herein to immobilize dispersed unsupported high area Pt particles (ca. 30 m 2 g −1) on the surface of a glassy carbon (GC) disk of a rotating Pt(ring)/GC(disk) electrode (RRDE) assembly, without the use of Nafion® or other additives, allowing electrochemical measurements to be performed under forced convection with only minimal losses of Pt from the surface. Diffusion limiting currents, I lim, and half-wave potentials for O 2 reduction recorded with dispersed Pt/GC electrodes at the highest attainable loadings (ca. 8.3 equivalent Pt monolayers and rotation rates 400≤ ω≤2500 rpm, were found to be differ only slightly from those observed with a bulk Pt RDE of the same cross sectional area, e.g. I lim(Pt) ca. 1.06 I lim(Pt/GC), under otherwise identical conditions. In addition, this novel strategy enables in situ surface modification of dispersed Pt particles on the GC disk of the RRDE by ad-atoms and subsequent voltammetric and electrocatalytic characterization for a wide spectrum of redox reactions.

Electrochemical Behavior of Menadione on Glassy Carbon Rotating Disk Electrode (RDE)

The 2-methyl-1,4-naphthoquinone electrochemical behavior on glassy carbon rotating disk electrode has been the focus of this study. In order to obtain the best results, the optimal conditions for this voltammetric study have been determined, by performing a chemometric analysis of the data. The influence of five factors on the diffusion current has been studied, finding that the greatest effect is due to three of them. The optimum values for all of these parameters were: pH 7, v (potential sweep rate)=87.1 mV/s, Cmet (methanol concentration)=4.14 %(v/v), teq (equilibrium time)=2.5 min, and tdea (purge time)=2 min. These data were used to determine the mass transfer parameters: diffusion coefficient (D=(1.4±0.3)×10–4 cm2/s) and diffusion layer thickness (δ=(6.6±0.5)×10–3 cm), the kinetic parameters: charge transfer constant (K0=2.91×10–6 cm/s) and charge transfer coefficient (α=0.248), and the standard potential (E0=0.083±0.011 V).

Electrochemical reduction of noble metal species in ethylene glycol at platinum and glassy carbon rotating disk electrodes

Linear sweep voltammetry has been used to delineate the electrochemical behavior of ethylene glycol, and to determine the reduction potential of several noble metal species in this solvent at room temperature. Ethylene glycol was found to be electrochemically inactive between −1.15 and 1.65 V at a glassy carbon electrode, and between −0.82 and 2.0 V at a Pt electrode. Metal reduction potentials determined using both rotating electrodes follow the sequence: AuCl 4 −>Ag +>PtCl 6 2−>Pd(NH 3) 4 2+. Under all conditions tested, ethylene glycol oxidation began at potentials more positive than metal reduction ones, thus suggesting that ethylene glycol cannot reduce these noble metal species. However, finely divided Ag and Au, were synthesized at room temperature by reduction of their corresponding ions with ethylene glycol (the basis of the polyol process). This observed difference between electrochemical results and chemical synthesis can be explained by recognizing that measured potentials are the sum of a thermodynamic potential and overpotential. Comparison between metal reduction potentials and temperature for metal particle synthesis indicates that the potential becomes more negative as the temperature increases. These results may provide useful information to better understand the fundamentals of the polyol process.

Rotating Disk Electrode Measurements on the CO Tolerance of a High‐Surface Area Pt/Vulcan Carbon Fuel Cell Catalyst

We examine the electrocatalytic properties of a Pt/Vulcan carbon catalyst toward the electro‐oxidation of CO and mixtures under proton exchange membrane fuel cell (PEMFC) relevant conditions (60 to 80°C, continuous reactant flow), employing rotating disk electrode (RDE) measurements. We demonstrate that our recently introduced thin‐film RDE technique can be applied to predict the performance of real fuel cell anodes operating on CO‐contaminated . The method involves attaching the catalyst particles to a glassy carbon RDE via a thin Nafion film. The thin‐film RDE technique opens the possibility for the mass‐transport‐free determination of the electrode kinetics at 100% catalyst utilization. At identical mass‐specific current densities, the overpotentials for oxidation measured with the thin‐film RDE technique are in excellent agreement with performance data from PEMFC anodes. The kinetics of pure CO oxidation were investigated with mixtures, revealing that the CO oxidation activity increases with decreasing CO partial pressure (negative reaction order). The observed ignition potential for CO oxidation was the same for both the and the mixtures. Two oxidation mechanisms in the presence of CO can be distinguished: (i) a high Tafel slope region at low overpotentials, where oxidation occurs in vacancies of the CO adlayer; and (ii) a low Tafel slope region at high overpotentials where and CO oxidation occur simultaneously. © 1999 The Electrochemical Society. All rights reserved.

Reaction mechanism and kinetics of alcohol oxidation at nitroxyl radical modified electrodes

Abstract Nitrosonium cations generated by the one-electron oxidation of nitroxyl radicals are known to serve as selective oxidizing agents for alcohols to aldehydes or ketones. We prepared glassy carbon rotating disk electrodes (RDE) modified with 2,2,6,6-tetramethyl-piperidinyl-1-oxyl (TEMPO) via a very thin layer of poly(acrylic acid) and studied the electrode processes of 4-methoxybenzyl alcohol oxidation taking place at the modified electrodes in acetonitrile solution containing 0.2 mol dm −3 sodium perchlorate using cyclic voltammetry and RDE voltammetry. It was found that though the presence of a base such as 2,6-lutidine is essential for the alcohol oxidation to proceed at a reasonable rate, the limiting current values corresponding to the rate of the alcohol oxidation at the RDE scarcely depend on the lutidine concentration. On the basis of these findings and electrochemical characteristics of TEMPO modified electrodes, we considered three possible reaction mechanisms and derived corresponding equations which relate the limiting current to rotation frequency of the RDE and concentrations of the alcohol and the base. We analyzed the experimental data by using the derived equations and proposed as the most probable reaction mechanism the one giving the most reasonable kinetic parameters and in which the rate-determining step is the decomposition of an intermediate formed from the nitrosonium cation, the alcohol and the base.

Study of mercury deposition from chloride solutions as test reaction for mass-transfer measurements

This paper deals with a systematic study of mercury deposition from sodium chloride solutions to determine the feasibility of using this reaction for mass-transfer measurements. The study was performed with a glassy carbon rotating disc electrode and reproducible results were obtained only when the electrode was catodically pretreated. Polarization curves at different concentrations of sodium chloride and mercury (ii) are reported. Hydrogen evolution and oxygen reduction has also been considered as side reactions and the conditions where their influence may be neglected are discussed. Experimental conditions where mercury deposition can be used as test reaction are given.

Some Consequences of the Significantly Different Mobilities of Hydrophilic and Hydrophobic Metal Complexes in Perfluorosulfonated Ionomer Coatings on Electrodes

Thin coatings of Nafion on glassy carbon rotating disk electrodes were saturated with hydrophilic [Ru(NH3)63+, Co(NH3)63+] or hydrophobic [Ru(bpy)32+] counterions. With both types of counterions, the plateau currents obtained when the electrodes were rotated in solutions of the cations matched the currents obtained with the uncoated electrodes in the same solutions at all accessible rotation rates. The high rates of cross-coating charge propagation demonstrated by these results involved physical diffusion of the hydrophilic complexes and electron hopping between adjacent, immobile pairs of the hydrophobic complexes. The approximate concentration profiles that develop within, and just outside of, Nafion coatings on disk electrodes that are rotated in solutions of electroactive counterions are depicted.

Electrodeposition of Hard Gold from Acidic Solution: The Influence of Substrates

Hard gold deposition from acidic solution on Au, Cu, Pt, Ni, and glassy carbon rotating disk electrodes was studied using linear sweep voltammetric (LSV) and chronoamperometric methods. A rotation rate‐dependent peak was found on LSV curves on various substrates. Such a peak arises from an inhibition process involved in gold deposition. The mechanism and kinetics of nucleation and crystal growth in the initial stages of gold deposition on different substrates were determined. Gold deposition on Au, Cu, and Pt at more positive potentials proceeds via three‐dimensional progressive nucleation and crystal growth of right‐circular cones. Potential‐dependent inhibition of crystal growth was also observed. A time‐dependent partial inhibition of crystal growth was found for deposition on Au, Ni, and glassy carbon electrodes at more negative potentials.

Long-time and short-time investigation of the electrode interface through electrochemical impedance measurements. Application to adsorption of human serum albumin onto glassy carbon rotating disc electrode

Abstract Two methods were used to investigate the adsorption of a human protein onto glassy carbon under well-defined conditions, i.e. in 0.1 M phosphate buffer (pH = 7.4), at T = 25°C, in the presence of equimolar (5 × 10−4 M) ferricyanide + ferrocyanide ions as steady-state indicator, with a three-electrode potentiostatic system at a bias potential of −0.67 V (SCE), under the laminar shear flow obtained by a carbon disc electrode rotated at 700 rev min−1. The protein concentration was 1 g dm−3. With the long-time method, the behaviour of the interface in its entirely was studied through the time-evolution of the impedance diagrams over a wide frequency range (sine-wave perturbation from 40 mHz to 10 kHz). With the short-time method, the time-evolution of the double-layer capacitance was determined at only one frequency, starting from the imaginary part of the impedance, on the basis of the well-known interface equivalent circuit without diffusion. However, investigation of the whole interface shoed that diffusion was actually indicated and the double-layer capacitance exhibited a fractional power-law (constant phase element) and was therefore frequency-dependent. The contribution of the characteristic electrical parameters of the interface in the overall impedance was determined. Use of the two methods justified the choice of the frequency value in the second method and showed the necessity of performing complete investigations of the interface over a wide frequency range before any capacitance measurements.

Spectrophotometric and Electrochemical Study of Gold‐Iodide in Aqueous Borate Medium

The constant‐current electrolysis technique was utilized to determine the oxidation state of gold in iodide media. The products from the electrolysis of gold metal in KI with 0.1 M borate were analyzed by means of electrogravimetry for gold and spectrophotometry for . At low current density, the gold species formed during the electrolysis process was Au(I) in KI with 0.1 M borate. Voltammetric measurements for the solution resulting from electrochemical dissolution of gold in on a glassy carbon rotating disk electrode enable us to measure the diffusion coefficient of Au(I) in the same medium, which was found to be . The equilibrium of the chemical reaction between gold and iodine in the medium of was also studied. The experimental results confirmed that the complex formed between Au(I) and iodide is . The stability constant for was determined by direct analysis of equilibrated solutions and was found to be .

Electrodeposition of Ni-W-B amorphous alloys

Partial polarization curves at the glassy carbon rotating disc electrode have been used to study the electrodeposition of Ni and Ni-W alloy from citrate-containing solution. For deposition of Ni-W alloys, the partial polarization curves indicate diffusion control for nickel reduction and stoichiometric limitation for tungsten deposition by the composition of the alloy. Plating experiments show that current efficiency of the electrodeposition and composition of the resulting alloy depend on the parameters of the electrolysis. The best conditions for electrodeposition of the alloy Ni-W-B are current density of 45–50 mA cm−2, temperature of 60–70 °C, Ni(II) concentration of 20–25 mm, and pH 8.5. Pulsed galvanostatic plating at 1 Hz increased slightly the current efficiency. The concentration of Ni(II) in the solution can be self-regulated by using a nickel bipolar electrode in the cathode compartment.

Electrochemical behavior of gold in iodide solutions

The electrochemistry of gold in different halide solutions, with special emphasis on iodide is presented. The electrochemical techniques used during this investigation included cyclic and linear sweep voltammetry. A glassy carbon rotating disk electrode was used to investigate the electrochemistry of the iodide and a gold rotating disk electrode to explore the oxidation behavior of gold in iodide solutions. The effects of iodide concentration, electrode rotation and sweep rate on the electrochemical behavior of gold were examined. In addition, reduction of iodine species at the gold electrode was also investigated. Iodide is shown to be a powerful complexing agent for gold. Cyclic voltammograms of gold in the presence of 10 −2 M chloride, bromide and iodide, respectively, show that the anodic currents for the oxidation of gold in iodide solution are much greater than that in either bromide or chloride. Two oxidation peaks, which represent the oxidations of Au to Au(I) and to Au(III), were observed. It is confirmed that iodide is oxidized sequentially to tri-iodide and then to iodine and both of these reactions are reversible. At high concentrations of iodide and/or a slow scan rate, passivation, which is caused by the formation of solid iodine at the gold electrode surface, was found. The cathodic reduction curves show that reduction of iodide species on gold is a function of iodine concentrations but it is insensitive to iodide concentration.

Simultaneous determination of nickel(II) and cobalt(II) by square-wave adsorptive stripping voltammetry on a rotating disc mercury film electrode

Adsorptive stripping voltammetry was used for the simultaneous determination of NiII and CoII; the metal ions were complexed with dimethylglyoxime and the complexes were adsorbed on the surface of a glassy carbon rotating disc electrode, which was pre-plated with mercury. The stripping step was carried out by using a square-wave potential–time excitation signal. An electrochemical cleaning of the mercury film was employed, enabling the same mercury film to be used for a series of measurements. The limits of detection were 12 ng l–1 for CoII and 14 ng l–1 for NiII(for 120 s preconcentration), the relative standard deviation was typically about 2–3%(at the 1.2 µg l–1 level) and linearity held for a concentration range of at least two orders of magnitude.

Analysis and physical significancy of the kinetic parameters associated with albumin adsorption onto glassy carbon obtained by electrochemical impedance measurements

The kinetics of albumin adsorption onto a glassy carbon rotating disk electrode in a phosphate buffer, is reported from the time variations of the double-layer capacitance C d, of the charge transfer resistance R t and of the Tafel coefficient of the electrochemical reaction b; these three electrical quantities are determined by electrochemical impedance and faradaic current I measurements. The variations of C d, 1/ R t, b  ( R t I) −1 and I can be written under the form: α 0 + α 1 e − t/τ1 + α 2 e − t/τ2 , where α 0, α 1, α 2, τ 1, τ 2 characterize a given electrical quantity. We demonstrate that this type of variation validates a two-step adsorption mechanism already proposed, starting from simply taking into account C d( t). We analyze and discuss comprehensively various possibilities of interpreting the shifts between the time-constants associated with thevarious quantities as well as the correlations between these constants and those associated with physical adsorption phenomena.

Analysis and physical significancy of the kinetic parameters associated with albumin adsorption onto glassy carbon obtained by electrochemical impedance measurements

The kinetics of albumin adsorption onto a glassy carbon rotating disk electrode in a phosphate buffer, is reported from the time variations of the double-layer capacitance C d, of the charge transfer resistance R t and of the Tafel coefficient of the electrochemical reaction b: these three electrical quantities are determined by electrochemical impedance and faradaic current I measurements. The variations of C d, 1/ R t, b  ( R t I) −1 and I can be written under the form: α 0 + α 1 e − t/τ 1 + α 2 e − t/τ 2 , where α 0, α 1, α 2, τ 1, τ 2 characterize a given electrical quantity. We demonstrate that this type of variation validates a two-step adsorption mechanism already proposed, starting from simply taking into account C d( t). We analyze and discuss comprehensively various possibilities of interpreting the shifts between the time-constants associated with the various quantities as well as the correlations between these constants and those associated with physical adsorption phenomena.