Linear Sweep Voltammograms Research Articles

Fast scan linear sweep voltammetry at a high-speed wall-tube electrode

The application of fast-scan linear sweep voltammetry methods to a high-speed wall-tube electrode (HWTE) is reported. Experiments are reported for the oxidation of N,N,N′ ,N′-tetramethyl- p-phenylenediamine (TMPD) in propylene carbonate solution containing 0.10 M tetrabutylammonium perchlorate for a 24 μm radius platinum microdisk electrode housed within the HWTE using a range of scan rates from 200 to 3000 V s −1 and average flow jet velocities from 0.24 to 9.4 m s −1 (corresponding to volume flow rates of 0.003–0.12 cm 3 s −1, and centre-line jet velocities from 0.5 to 18.9 m s −1). Linear sweep voltammograms (LSVs) are analysed for a simple electron transfer under high volume flow rates, by curve fitting. Analysis of the transient LSVs yielded values for k 0, α, and E f 0 for TMPD of (5.9±2.4)×10 −2 cm s −1, 0.46±0.08 and 0.217±0.019 V (vs. Ag), respectively. This is in good agreement with independent experiments conducted using the high-speed channel electrode which yielded the results: k 0=(6.3±0.4)×10 −2 cm s −1, α=0.52±0.01, and E f 0 =0.234±0.005 V (vs. Ag). The range of applicability of this method for measuring k 0 was also investigated and compared with existing channel electrode techniques.

Electroreduction Behavior of Dinitrogen over Ruthenium Cathodic Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electroreduction Behavior of Dinitrogen over Ruthenium Cathodic Catalyst

Abstract Dinitrogen was reduced electrochemically at ambient temperature and pressure in aqueous solution over ruthenium catalyst. It was found that the chemically deposited ruthenium loaded on active carbon was an effective catalyst with good activity and stability for nitrogen reduction. A peak with many shoulders corresponding to the reduction of dinitrogen to ammonia was first observed in the difference linear sweep voltammogram.

Electrocatalytic properties of mechanically alloyed Co-20wt%Ni-10wt%Mo and Co-70wt%Ni-10wt%Mo alloy powders

Mechanically alloyed Co-20wt%Ni-10wt%Mo and Co-70wt%Ni-10wt%Mo (nominal compositions) alloy powders were produced by milling of pure elemental powders. Mechanically alloyed powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. MA powder specimens were tested electrollitically in a 30% KOH aqueous solution at 298 K. X-ray diffraction analysis and transmission electron microscopy of milled powders showed the presence of two phases, an fcc solid solution and intermetallic compounds of Ni or Co with Mo. These phases showed a nanometric size. The linear sweep voltammograms confirmed also the presence of two phases in both mechanically alloyed alloy powders. The Co-20wt%Ni-10wt%Mo alloy powders showed the best electrocatalytic activity for hydrogen evolution reaction.

Anodic deposition of nickel oxides for the nickel-based batteries

This work represented the preliminary results in developing the anodic deposition of nickel oxides and examining their electrochemical and textural properties for the application in aqueous batteries. Nickel oxides were anodically deposited onto the graphite substrate by cyclic voltammetry (CV) and potentiostatic techniques from the aqueous solution containing NiCl 2. Based on the linear sweep voltammogram (LSV) measured from the chloride solution, the anodic deposition of nickel oxides commenced at the onset of the Ni(II)/Ni(III) transition. The electrochemical characteristics, including the specific charge capacity and charge–discharge reversibility, of nickel oxides prepared by the anodic deposition were demonstrated to be the promising electrode materials for nickel-based batteries, which were obviously affected by the potential ranges of CV and the potentials of potentiostatic deposition. The morphologies and crystalline structures of these nickel oxides were respectively examined by scanning electron microscopic photographs and X-ray diffraction (XRD) spectra.

Lithium transport through a sol–gel derived LiMn 2O 4 film electrode: analyses of potentiostatic current transient and linear sweep voltammogram by Monte Carlo simulation

Lithium transport through a sol–gel derived LiMn 2O 4 film electrode was theoretically investigated by analyses of the potentiostatic current transient and the linear sweep voltammogram in consideration of the interactions between lithium ions by using Monte Carlo simulation. The anodic current transients experimentally measured on the film electrode ran with the slope of logarithmic current with logarithmic time flatter than −0.5 in the early stage, and then did in an upward concave shape in the time interval between t T1 and t T2. The linear sweep voltammograms experimentally measured on the film electrode showed two anodic peak currents I p1 and I p2 which increased linearly with scan rate v to the power of 0.66 and 0.70, respectively, (i.e. I p1∝ v 0.66 and I p2∝ v 0.70) at the scan rates higher than 0.5 mV s −1. Moreover, the higher v was, the larger appeared the positive deviations of the first and second peak potentials E p1 and E p2 from the first and the second transition potentials E° p1 and E° p2, respectively, in the inverse derivative of the electrode potential curve. The current transients and the linear sweep voltammograms were analyzed in consideration of the interactions between lithium ions in the electrode by using the Monte Carlo simulation under two different constraints of the diffusion-controlled lithium transport and the cell-impedance-controlled lithium transport. The current transients and the linear sweep voltammograms, theoretically calculated under the cell-impedance-controlled constraint in consideration of the interactions between lithium ions, were in good agreement with the experimental results in shape. The disorder to order phase transition in the LiMn 2O 4 film electrode during the cell-impedance-controlled lithium transport at the potential jump and scan was discussed with the aid of the concentration profiles and the local cross-sectional snapshots of the configuration of lithium ions simulated by the Monte Carlo method.

Application of Monte Carlo Simulation to Intercalation Electrochemistry II. Kinetic Approach to Lithium Intercalation into LiMn2O4Electrode

속도론적 관점에서 키네틱 몬테 카를로 방법의 전기화학적 리튬 인터칼레이션에로의 응용에 대하여 다루었다. 우선 키네틱 몬테 카를로 방법과 전이상태이론의 기본 개념을 소개하였고, 확산거동을 평가하기 위한 시뮬레이션 과정을 설명하였다. 마지막으로 인터칼레이션 화합물중 <TEX>$LiMn_2O_4$</TEX>전극에 대해 전류 추이곡선과 선형 포텐셜 전류곡선을 해석하기 위해서 전이상태이론에 근거한 키네틱 몬테 카를로 방법을 셀-저항 제어조건하에서 사용하였다. 이로부터 키네틱 몬테 카를로 방법이 전기화학분야에서 리튬 인터칼레이션의 속도론적 연구에 매우 유용함을 알 수 있었다. The present article is concerned with the application of the kinetic Monte Carlo simulation to electrochemistry of lithium intercalation from the kinetic view point. Basic concepts of the kinetic Monte Carlo method and the transition state theory were first introduced, and then the simulation procedures were explained to evaluate diffusion process. Finally the kinetic Monte Carlo method based upon the transition state theory was employed under the cell-impedance-controlled constraint to analyse the current transient and the linear sweep voltammogram for the <TEX>$LiMn_2O_4$</TEX> electrode, one of the intercalation compounds. From the results, it was found that the kinetic Monte Carlo method is much relevant to investigate kinetics of the lithium intercalation in the field of electrochemistry.

Determination of Hg22+Ions Using a Modified Glassy Carbon Electrode with 2,2':6':2''-Terpyridine

A glassy carbon electrode (GCE) modified with 2,2':6':2”-terpyridine (2,2':6':2”-TPR) using a spin coating method was applied for the highly selective and sensitive analysis of a trace amount of <TEX>$Hg_2^{2+}$</TEX> ions. Various experimental parameters, which influenced the response of the 2,2':6':2”-TPR modified electrode to <TEX>$Hg_2^{2+}$</TEX> ions, were optimized. The linear sweep and differential pulse voltammograms for the 2,2':6':2”-TPR modified electrode deposited with Hg show a well-defined anodic peak at +0.65 V (vs. Ag|AgCl). After a 25 min preconcentration time in an <TEX>$Hg_2^{2+}$</TEX> ion solution (0.1 M acetate buffer, pH 5.0), differential pulse voltammetry(DPV) with 2,2':6':2”-TPR modified electrode shows a linear response between <TEX>$1.0\;{\times}\;10^{-6}M\;and\;2.0\;{\times}\;10^{-7}M$</TEX>. The least-square treatment of these data produce an equation of I[<TEX>${\mu}A$</TEX>] = 0.031 + 0.005C with r = 0.980(n = 5). The detection limit of this electrode with linear sweep voltammetry and differential pulse anodic voltammetry were <TEX>$2.0\;{\times}\;10^{-6}M\;and\;8.0\;{\times}\;10^{-8}M$</TEX>, respectively. The presence of Pb, Fe, Cd, Ti, Ni, Co, Mg, Al, Mn, and Zn did not interfere in the analysis of the <TEX>$Hg_2^{2+}$</TEX> ion. The 2,2':6':2”-TPR modified GCE has been successfully applied in determination trace amounts of Hg in a human urine sample.

Use of dynamically adaptive grid techniques for the solution of electrochemical kinetic equations. Advantage of time step adaptation, using example of current spikes in linear potential sweep voltammograms for the EqrevEqrev-DISP reaction mechanism

Electrochemical kinetic transients may exhibit brief, but rapid temporal variations, the location of which along the time axis, and duration, are difficult or impossible to predict. For example, very narrow current spikes may occur on linear potential sweep voltammograms for the E qrev E qrev-DISP reaction mechanism. Traditional fixed time grids require a dense grid spacing over large time intervals in such cases, which renders digital simulations computationally expensive. In contrast, the adaptive time step selection, included into the previously described finite-difference patch-adaptive strategy (PAS), enables a detailed temporal resolution of the current spikes, simultaneously with an efficient simulation of large-scale temporal variations. Using this technique, the phenomenon of the current spikes is investigated.

Solid deposits of osmium bis-bipyridyl triazole chloride: Redox properties and electrocrystallisation

Mechanically attached, solid-state films of [Os(bpy)2 bpt Cl] have been formed on platinum microelectrodes and their voltammetric properties investigated, bpy is 2,2′-bipyridyl and bpt is 3,5-bis(pyridin-4-yl)-1,2,4-triazole. Scanning electron microscopy reveals that voltammetric cycling in 1.0 M HClO4 converts the amorphous array of microscopically small particles into a plate-like semi-crystalline form. In contrast, crystallisation does not occur when the films are cycled in 1.0 M NaClO4. In both electrolytes, the voltammetric response of these films is reminiscent of that observed for an ideal reversible, solution phase redox couple. Slow and fast scan linear sweep voltammograms have been used to provide an absolute determination of the fixed site concentration and apparent diffusion coefficient, Dapp. The fixed site concentration is 1.65 ± 0.05 M for films cycled in either electrolyte and the Dapp values increase with increasing electrolyte concentration, Celec. These observations suggest that ion transport rather than the rate of electron self-exchange limit the overall rate of charge transport through these solids. In 1.0 M NaClO4, Dapp values for oxidation and reduction are identical at 8.3 ± 0.5 × 10−12 cm2 s−1. In 1.0 M HClO4, Dapp is significantly lower and depends on whether the deposit is being oxidised (9.7 ± 0.4 × 10−13 cm2 s−1) or reduced (6.3 ± 0.4 × 10−13 cm2 s−1). These data have been used to obtain an insight into the relative importance of intra- s. inter-particle charge transport. When Celec>0.5 M, the standard heterogeneous electron transfer rate constant, k°, becomes independent of the electrolyte concentration with a value of 1.7 ± 0.2 × 10−5 cm s−1 being observed in both 1.0 M NaClO4 and HClO4. Significantly, the distance normalised heterogeneous electron transfer rate constant for these solid state films is almost three orders of magnitude smaller than that found within a spontaneously adsorbed monolayer of the same complex. The importance of these results for the rational design of solid-state redox active materials for battery, display and sensor applications is considered.

Corrosion and erosion-corrosion of electrodeposited Ni–P/B4C composites

Abstract The present paper reports on electrodeposition, characterisation, corrosion, and erosion–corrosion of Ni–P and Ni–P/B4 C layers on a brass substrate. Alloys with 5%P and 8 vol.-% micrometric B4 C were prepared from a lactate bath at pH 4 containing H3 PO3 . The following deposit properties were measured and related to corrosion behaviour: composition (EDS, XPS), crystalline structure (XRD), morphology (inplane and cross-sectional SEM), and mechanical properties. The immersion and anodic behaviour of pure matrix and composite samples was studied in slightly acidic, aerated chloride solutions. The presence of B4 C particles is correlated with higher crystallinity of the matrix at a given P content. Anodic linear sweep voltammograms show more noble breakdown potentials and lower plateau current densities for the composites. The pit-arresting effect of particle addition was assessed. More noble corrosion potentials and much lower mass losses, pitting, and crevice formation were observed under erosion...

Voltammetry on microfluidic chip platforms

Microfluidic chip devices are shown to be attractive platforms for performing microscale voltammetric analysis and for integrating voltammetric procedures with on-chip chemical reactions and fluid manipulations. Linear-sweep, square-wave, and adsorptive-stripping voltammograms are recorded while electrokinetically "pumping" the sample through the microchannels. The adaptation of voltammetric techniques to microfluidic chip operation requires an assessment of the effect of relevant experimental variables, particularly the high voltage used for driving the electroosmotic flow, upon the background current, potential window, and size or potential of the voltammetric signal. The exact potential window of the chip detector is dependent upon the driving voltage. Manipulation of the electroosmotic flow opens the door to hydrodynamic modulation (stopped-flow) and reversed-flow operations. The modulated analyte velocity permits compensation of the microchip voltammetric background. Reversal of the driving voltage polarity offers extended residence times in the detector compartment. Rapid square-wave voltammetry/flow injection operation allows a detection limit of 2 x 10(-12) mol (i.e., 2 pmol) of 2,4,6-trinitrotoluene (TNT) in connection with 47 nL of injected sample. The ability of integrating chemical reactions with voltammetric detection is demonstrated for adsorptive stripping measurements of trace nickel using the nickel-dimethylglyoxime model system. The voltammetric response is characterized using catechol, hydrazine, TNT, and nickel as test species. The ability to perform on-chip voltammertic protocols in advantageous over nanovial voltammetric operations that lack a liquid-handling capability. Coupling the versatility of microfluidic chips with the rich information content of voltammetry thus opens an array of future opportunities.

A contribution to the knowledge of electrochemical deposition of W induced by Ni

It was found that codeposition of Ni and W from an ammonia and citrate-containing electrolyte, is very sensitive to changes in operating conditions. The Ni–W alloy deposit exhibited sensitivity of chemical composition and phase structure on the composition of the electrolyte, pH in particular, as well as on the current density (cd), hydrodynamic conditions and quantity (thickness) of the deposit. Thus, small changes in pH, which arise during the process of bath utilization, are found to change the relationships between peaks in anodic dissolution voltammograms reflecting the existence of different phases. The anodic linear sweep voltammograms (ALSV) of the alloys deposited at medium cds, pH lower than 8.4 and a high rate of rotation of the RDE contained two peaks. The first one could be ascribed to some tungsten oxide species while the appearance of the second one basically reflects the presence of solid solution of W in Ni, but also points to some other phases. The increase in pH, increase in cd, and the decrease in the rate of rotation of the RDE all lead to ALSV with a single peak with a peak potential shifted in the negative direction, i.e. towards the dissolution peak of pure Ni. Analysis confirmed a decrease of W content in that shift. Still a somewhat more noble behavior than that of Ni points out that some W still remains in the Ni.

Azo compounds as reagents for the voltammetric determination of molybdenum(VI)

Linear sweep voltammograms of Lumogallion IREA (pH 2), Magneson IREA (pH 2), 4-(2-pyridylazo)resorcinol (pH 4.8), and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (pH 4.8) in the presence of molybdenum(VI) exhibit peaks at potentials more negative than the potentials of reduction peaks of the reagents by approximately 0.1 V. In all of the above cases, the heights of these peaks linearly increased with an increase in the concentration of molybdenum(VI) in the range from 5 x 10-7 to 2.5 x 10-6 M; thus, these peaks can be used for the determination of molybdenum. The simultaneous proportional decrease in the heights of the cathodic peaks of the reagents can be used for indirect determination of molybdenum(VI). The limits of detection without preliminary accumulation at a dropping mercury electrode with a drop time of 5 s are (1.5-3.9) x 10-7 M, depending on the nature of the reagent and the technique used for determining the concentration.

Protonation Effects on the Structure and Homogeneous Charge Transport Dynamics of Solid State Osmium Bis(bipyridyl)tetrazine Chloride Films

Mechanically attached solid state films of [Os(bpy)2-4-tet-Cl](ClO4) have been formed on platinum microelectrodes (where bpy is 2,2‘-bipyridyl and 4-tet is 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine). Scanning electron microscopy reveals that films exist as an amorphous array of microscopically small particles. At relatively high scan rates, the voltammetric response of these films is reminiscent of that observed for an ideal reversible, solution phase redox couple. The film structure is not affected by voltammetric cycling in perchloric acid which protonates the unbound pyridine moiety of the tetrazine ligand. In contrast, the films become significantly more homogeneous when cycled in sodium perchlorate electrolyte and appear to become microcrystalline. Slow and fast scan linear sweep voltammograms have been used to provide an absolute determination of the fixed site concentration as 1.8 ± 0.05 and 1.6 ± 0.06 M and apparent diffusion coefficients of (6.4 ± 0.3) × 10-11 and (5.0 ± 0.4) × 10-11 cm2 s-1 in 1.0 M ...

Influence of the local electric field on ionic transport during redox switching of conducting polymers

This work aims to demonstrate the predominant role played by migration in ionic transport during redox switching of conducting polymers. For this purpose, we apply the “moving front” model in addition to a field driven motion of dopant ions. The local electric field inside the film is calculated by numerically solving the Poisson equation. Simulation of linear sweep voltammograms is performed using a Monte-Carlo procedure, and the shapes of the resulting curves are analysed, in relation with the dielectric constant of the film and the potential scan rate. The evolutions observed for the simulated voltammograms are correlated to the local electric field profiles. So, it has been demonstrated that the space charges created at the beginning of the oxidation process act as a barrier for the incorporation of dopants. This behaviour is observed as long as the electrode potential is not too high above the standard potential. These results differ notably from those established in the case of pure diffusional ionic motion.

Voltammetric determination of butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate and tert-butylhydroquinone by use of chemometric approaches

The voltammetric behavior of synthetic food antioxidants, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and tert-butylhydroquinone (TBHQ), at a glassy carbon electrode in solution of 0.1 mol l −1 perchloric acid containing 1% methanol has been investigated. The obtained linear sweep voltammograms (LSV) showed that all these four compounds have well-defined oxidation waves with peak potentials of 629, 818, 599 and 501 mV for BHA, BHT, PG and TBHQ, respectively. Linear calibration graphs were also obtained in the concentration ranges of 0.5–15.0, 0.5–8.0, 1.0–15.0 and 1.0–15.0 mg l −1 for BHA, BHT, PG and TBHQ, respectively. However, the voltammetric peaks of these antioxidants seriously overlap and it is difficult to determine them individually from a mixture without prior separation. In this work, a method for simultaneous determination of these antioxidants, based on their oxidation at the glassy carbon electrode, with the aid of chemometric approaches, such as classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS), has been developed. The method was applied to determine the four antioxidants in a set of synthetic mixtures and several commercial food samples; in general, satisfactory results were obtained.

A Simple Numerical Procedure for the Simulation of "Lifelike" Linear-Sweep Voltammograms

Practical linear-sweep voltammograms seldom resemble the theoretical ones shown in textbooks. This is because several phenomena (activation, mass transport, ohmic resistance) control the kinetics over different potential ranges scanned during the potential sweep. These effects are generally treated separately in the didactic literature, yet they have never been assembled in a way that allows the educational use of real experiments. This makes linear-sweep voltammetric experiments almost unusable in the teaching of physical chemistry. A simple approach to the classroom description of lifelike experimental results is proposed in this paper. Analytical expressions of linear sweep voltammograms are provided. The actual numerical evaluations can be carried out with a pocket calculator. Two typical examples are executed and comparison with experimental data is described. This approach to teaching electrode kinetics has proved an effective tool to provide students with an insight into the effects of electroc...

Electrochemical Oxidation of Chlorinated Phenols

Electrochemical oxidation has been proposed as a remediation method for chlorinated phenols but is hampered by anode fouling. In this work we explore the mechanism of anode fouling by chlorinated phenols, compare structure vs reactivity for phenols differing in the extent of chlorination, and relate the efficiency of oxidation to the mechanism of oxidation at different electrode types. Linear sweep voltammograms at a Pt anode at several concentrations, sweep rates, and pH were interpreted in terms of deposition of oligomers on the anode surface. Chronopotentiometry at Pt showed that the oxidation potentials of the chlorinated phenol congeners ranged from +0.6 to +1.3 V vs SHE in the pH range 2−12; four electrons are transferred for mono- and trichlorophenols and two for pentachlorophenol. Passivation increased in parallel with the uncompensated resistance of the solution and occurred only at potentials at which water is oxidized, suggesting that the formation of the oligomer film involves attack of hydrox...

Zirconium and Ebonex® as cathodes for sulphite ion oxidation in sulphuric acid

The electrochemical behaviour of zirconium metal and Ebonex® cathodes during the electrolysis of sulphite ions in sulphuric acid, at temperatures from 20 to 90 ∘C, is reported. The inactivity of these materials for the reduction of sulphite ions to sulphur is demonstrated, making the undivided cell oxidation of sulphite ions to sulphuric acid, at concentrations greater than 3.0 mol dm−3, a viable process. The use of these two cathodes materials in conjunction with lead dioxide-coated and palladium oxide-coated anodes for sulphite ion oxidation is described. Linear sweep voltammograms, chronopotentiometry and batch electrolysis data are presented for sulphite ion oxidation and demonstrate the concept of an undivided electrolysis for the oxidation of sulphur dioxide in sulphuric acid.