Potentiostatic Current-time Transients Research Articles

Electrochemical nucleation and growth of Pt nanoflower particles on reduced graphite oxide with electrooxidation of glucose.

Electrochemical deposition of platinum nanoflower particles (PtNFPs) on reduced graphite oxide, rGO/GCE, using H2PtCl6 electrolyte in H2SO4 solution was investigated by chronoamperometry (CA). The experimental i-t curves measured at different overpotentials were analyzed and compared with theoretical curves obtained for the two limiting cases of the 3D nucleation and growth model, as described by Scharifker and Hills. The effect of deposition overpotential on the deposition process was evaluated. Through comparing potentiostatic current-time transients with the Scharifker-Hills model, a transition from instantaneous to a mixed kind of progressive-instantaneous nucleation was observed when increasing the deposition overpotential. CA results clearly show that the electrodeposition processes are diffusion-controlled (D0 = 2.77 × 10-5 cm2 s-1). A finer distribution of PtNFPs with an average size of ∼70 nm was obtained in 1.0 mM H2PtCl6 electrolyte in a 0.5 M H2SO4 solution. The as-prepared PtNFP/rGO catalyst shows 1.5 times higher activity than rGO/GCE, and the catalytic activity towards glucose oxidation is about many fold higher than that of the rGO/GCE and bare platinum electrode.

Electrochemical behaviour of hydrogen evolution reaction on platinum in anhydrous ethanol containing tetraethylammonium bromide

The electrochemical behaviour of hydrogen evolution reaction (HER) on platinum in anhydrous ethanol-containing tetraethylammonium bromide was investigated using potentiodynamic polarization, open-circuit potential measurement, potentiostatic current–time transient, galvanostatic potential–time transient, impedance and surface appearance observation techniques. The potentiodynamic polarization curves revealed that the HER process had two stages with larger Tafel slopes in this solution. Such higher slopes might result from the presence of adsorbates on the Pt surface which act as a barrier for HER. The study of ultrasonic-wave impact on potentiodynamic polarization indicated that the desorption of the adsorbates including hydrogen atoms could be enhanced by ultrasonic wave. The hydrogen evolution potential (Eh) shifted to more noble values with increasing scanning rate and solution temperature. Surface appearance observations of the Pt surface demonstrated the existence of hydrogen evolution, presenting the growth of the hydrogen evolution. The potentiostatic current–time transients indicated that HER occurred on Pt at potentials more negative than Eh. The galvanostatic potential/time transients showed that the applied negative current density exerted a great influence on the values of Eh. The impedance spectra at potentials more negative than Eh exhibited two time constants at less-negative potentials, but just one time constant at higher negative potentials.

Pitting Corrosion of Zn Peculiarly Caused by Acetate Anions

Abstract The corrosion behaviour of zinc metal was studied in acetate solutions. The potentiodynamic polarization curve in 0.1 M acetate solution displays an anodic peak (A1) owing to the anodic dissolution of zinc followed by a passive layer formation region. Breakdown of the passive film and the initiation of pitting corrosion were observed beyond the pitting potential (E pit) and confirmed by SEM images. The reverse scan of the cyclic voltammogram shows three cathodic peaks; CI, CII and CIII. CI was attributed to the reduction of the pitting corrosion product formed at potentials more anodic than E pit, while the overlapped CII and CIII peaks were attributed to the reduction of the exterior and the interior passive layers, respectively. The potentiostatic current time transients at different applied potentials (around the pitting potential) for different electrolyte concentrations involved three stages. The first stage exhibited rapid current decrease with time till a minimum value (i m) at the incubation time (t i). The second and the third stages, where the current increases again linearly with time through two different slopes, are correlated to the pit nucleation and growth, respectively. An increase of the pit nucleation rate and a decrease in its growth were observed with increasing the anodic potential limit (E a). Electrochemical impedance spectroscopy (EIS) measurements, at different potentials before and after E pit were performed. The effect of the acetate concentration was studied as well. A suggested equivalent circuit was used to fit the EIS data. The impedance results confirmed that the thickness of the formed passive layer increases with proceeding of the anodic potential reaching a maximum value at E pit. The passive film thickness decreased again at more anodic potentials.

Mechanism for nucleation and growth of electrochemical deposition of palladium(II) on a platinum electrode in hydrochloric acid solution

Palladium(II) and chloride ions tend to form complexes in aqueous solution. Both theoretical and experimental (by UV spectrum) results indicate that there are four complexes formed in aqueous solution containing 3 mol/L hydrochloric acid and 20 mmol/L PdCl2. This work evaluates the kinetics of electrochemical deposition of palladium on a Platinum electrode. For this purpose, palladium electrodeposition was investigated by means of cyclic voltammetry (CV), potentiostatic current-time transients (CTTs) and Tafel curve. By CTTs curves, the regions corresponding to the charge transfer control, mixed control and diffusion control were identified. In the diffusion control region, palladium electrodeposition mechanism was characterized as progressive nucleation with three-dimensional (3D) growth under diffusion control; as for the mixed control region, an adsorption (IAds), ion transfer (IIT), and nucleation and growth (ING) model were proposed to analyze the current-time transients quantitatively, which could separate the IAds, IIT and ING perfectly.

Electrochemical Behavior of Cu-Ag Alloys in Perchlorate Solutions Using Cyclic Voltammetric and Current Transients Techniques

The electrochemical behavior of Cu-Ag system was studied in 0.5 M NaOH and sodium perchlorate by means of cyclic voltammetry, potentiodynamic anodic polarization and current/ time transients techniques. SEM and EDX microanalysis were used to examine the changes caused by the electrochemical perturbations. In perchlorate free alkali solution the anodic portion of the voltammogram was characterized by the existence of two potential regions I and II. In the first potential region copper dissolves preferentially and exhibits three anodic peaks A1, A2 and A3. The anodic peak A1 was related to the formation of Cu2O while the anodic peaks A2 and A3 are related to the oxidation of Cu and Cu2O, respectively to CuO and Cu(OH)2. The preferential dissolution of copper was enhanced and the simultaneous dissolution of silver was retarded on increasing the silver content in the alloy. The potential region II was characterized by the appearance of three anodic peaks A4, A5 and A6 which are related o the formation of mono-layer, and multi-layers of Ag2O, AgO and Ag2O3, respectively. The addition of increasing amounts of ClO4 - increases the heights of the anodic peaks and above a limiting value breakdown the anodic passivity and initiate pitting corrosion. The pitting potential decreases linearly with ClO4 - concentration but increases with increasing scan rate. The potentiostatic current time transients show that the pitting corrosion can be described in terms of an instantaneous three dimensional grows under diffusion control. X-ray diffraction analysis was used to determine the composition of the corrosion products on the electrode surface. Scanning electron microscope was used to monitor pitting corrosion and to elucidate the effect of constituents on the alloy dissolution.

A kinetic description of Pd electrodeposition under mixed control of charge transfer and diffusion

This work evaluates the kinetics of Pd nanoparticles nucleation and growth at the potential range where electrodeposition is controlled by both charge transfer and diffusion. For this purpose, Pd electrodeposition from an aqueous solution containing PdCl2 (0.001M) and H2SO4 (0.5M) was studied by means of cyclic voltammetry and potentiostatic current–time transients (CTTs). Using the polarization curves, regions corresponding to charge transfer control, mixed control and diffusion control were identified. In mixed control region, CTTs study suggested the presence of three processes involving adsorption, the ion transfer reaction and 3D progressive nucleation with mixed charge transfer-diffusion controlled growth. The kinetic parameters at different electrode potentials within the mixed control region were estimated through the analysis of CTTs at short times in accordance with the model proposed by Milchev and Zapryanova. It was found that the reduction reaction of Pd(II)→Pd(I) – as an ion transfer reaction – occurs before the formation of Pd nucleus and its corresponding ion transfer coefficient was estimated αi=0.33.

Electrochemical Behavior of Gold Nanoparticles Modified Nitrogen Incorporated Tetrahedral Amorphous Carbon and Its Application in Glucose Sensing

Gold nanoparticles (NPs) with 10-50 nm in diameter were synthesized on nitrogen incorporated tetrahedral amorphous carbon (ta-C:N) thin film electrode by electrodeposition. The deposition and nucleation processes of Au on ta-C:N surface were investigated by cyclic voltammetry and chronoamperometry. The morphology of Au NPs was characterized by scanned electron microscopy. The electrochemical properties of Au NPs modified ta-C:N (ta-C:N/Au) electrode and its ability to sense glucose were investigated by voltammetric and amperometric measurements. The potentiostatic current-time transients showed a progressive nucleation process and diffusion growth of Au on the surface of ta-C:N film according to the Scharifker-Hills model. The Au NPs acted as microelectrodes improved the electron transfer and electrocatalytic oxidation of glucose on ta-C:N electrode. The ta-C:N/Au electrode exhibited fast current response, a linear detection range of glucose from 0.5 to 25 mM and a detection limit of 120 microM, which hinted its potential application as a glucose biosensor.

Uniform and pitting corrosion events induced by SCN− anions on Al alloys surfaces and the effect of UV light

The influence of the alloying elements on the uniform and pitting corrosion processes of Al-6061, Al–4.5%Cu, Al–7.5%Cu, Al–6%Si and Al–12%Si alloys was studied in 0.50M KSCN solution at 25°C. Open-circuit potential, Tafel polarization, linear polarization resistance (LPR) and ICP-AES measurements were used to study the uniform corrosion process on the surfaces of the tested alloys. Cyclic polarization, potentiostatic current-time transients and impedance techniques were employed for pitting corrosion studies. Obtained results were compared with pure Al. Passivation kinetics of the tested Al samples were also studied as a function of applied potential, [SCN−] and sample composition by means of potentiostatic current transients. The induction time, after which the growth of stable pits occurs, decreased with increasing applied potential and [SCN−]. Regarding to uniform corrosion, alloyed Cu was found to enhance the corrosion rate, while alloyed Si suppressed it. Alloying elements of the tested samples diminished pitting attack to an extent depending on the percentage of the alloying element in the sample. Among the investigated materials, Al–Si alloys exhibited the highest corrosion resistance towards uniform and pitting corrosion processes in KSCN solutions. The passive and dissolution behaviour of Al was also studied under the conditions of continuous illumination (300–450nm) based on cyclic polarization and potentiostatic techniques. The incident photons had a little influence on pit initiation and a marked effect on pit growth. These explained in terms of a photo-induced modification of the passive film formed on the anode surface, which render it more resistant to pitting. The effects of UV photons energy and period of illumination on the morphology of the pitted surfaces were also studied.

Electrochemical Behavior of Tantalum in Anhydrous Ethanol

The electrochemical behaviors of Ta in ethanol solutions were investigated using potentiodynamic polarization, cyclic voltammetry, and potentiostatic current–time transient techniques, complemented with a scanning electron microscope (SEM). The potentiodynamic anodic polarization curves did not exhibit an active dissolution region due to the presence of a thin oxide film on the electrode surface, which was followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of anions. SEM images confirmed the existence of pits on the electrode surface. The pitting potential decreased with the increase in solution temperature, but increased with increasing potential scan rate. The potentiostatic current–time transients showed that the incubation time slightly decreased with increasing concentrations. The pitting growth current density agreed well with Hills’s model.

Effect of bromide ions on the corrosion behavior of tantalum in anhydrous ethanol

The electrochemical behaviors of Ta in Et 4NBr ethanol solutions were investigated using potentiodynamic polarization, cyclic voltammetry, potentiostatic current–time transient and impedance techniques. The potentiodynamic anodic polarization curves did not exhibit active dissolution region due to the presence of thin oxide film on the electrode surface, which was followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of Br − anions. The pitting potential ( E b) decreased with the increase of solution temperature and Br − concentration, but increased with increasing potential scan rate and water concentration. The incubation time derived from potentiostatic current–time transients decreased with increasing potentials. The impedance spectra exhibited two time constants for all the potentials and the resistance of passive layer decreased with increasing potential.

Correlation between morphology and NGM of 3,4- ethylenedioxythiophene (EDOT) in acetonitrile

AbstractThe nucleation and growth mechanism (NGM) for the electro-oxidation of 3,4-ethylenedioxythiophene (EDOT) in acetonitrile on platinum and tin(IV) oxide electrodes was determined by analyzing the potentiostatic current-time transients inferred from electrocrystallization theory. The measurements were complemented by using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Preliminary studies performed to establish the working conditions for the potentiostatic technique using cyclic voltammetry (CV) demonstrated that under the working conditions employed herein the best potential scan-rate to obtain electrodeposits of poly(EDOT) was 50 mV·s-1. The prepared polymer displayed electrochromic properties and p- and n-doping, the p-doping being chemically reversible. In addition, it was observed that the electropolymerization mechanisms on both electrode materials were a combination of two contributions: progressive nucleation, followed by diffusion-controlled tridimensional growth, PN3Ddif; and instantaneous nucleation followed by three-dimensional growth under charge transfer control, IN3Dct. At shorter times, the IN3Dct contribution prevail giving rise to conical deposits, while at longer electrolysis times the polymeric deposit is made of granules, corresponding to the PN3Ddif mechanism. The electrode material has no effect at all on the global mechanism, but affects the time at which either contribution predominates. However, the morphological predictions made from the NGMs must be corroborated by other techniques before using the data to control the deposit to be prepared.

Black nickel electrodeposition from a modified Watts bath

Black nickel coatings were electrodeposited on to steel substrates from a Watts bath containing potassium nitrate. The best operating conditions necessary to produce smooth and highly adherent black nickel were found to be NiSO4 · 6H2O 0.63 M, NiCl2 · 6H2O 0.09 M, H3BO3 0.3 M and KNO3 0.2 M at pH of 4.6, i=0.5 A dm−2, T=25 °C and t=10 min. The modified Watts bath has a throwing power (TP) of 61%, which is higher than that reported, not only for nickel, but also for many other metals electrodeposited from different baths. The potentiostatic current–time transients indicate instantaneous nucleation. X-ray diffraction (XRD) analysis shows that the black nickel deposit is pure metallic nickel with Ni(111) preferred orientation.

Kinetics of Two-Phase Electrocrystallization Processes: III. Competitive Nucleation and Growth of Hemispheroids

The forms of the potentiostatic current-time transients (CTTs) were derived for the kinetically controlled growth of two crystallographic phases of right circular conical contours in the previous paper of this series. In the present paper, each phase is assumed to have formed from the growth of nuclei of hemispheroidal geometry of a distinct eccentricity. The forms of the CTTs, resulting from the growth of these centers, are then derived and compared with those recorded during the electrocrystallization of zinc. It is shown that at least in the early stages of electrocrystallization of zinc, two distinct types of deposits each with its own characteristic morphology is formed.

Effect of chloride ions on the corrosion behaviour of steel in 0.1 M citrate

The corrosion behaviour of steel was studied in aerated near neutral citrate solutions without and with various concentrations of NaCl. The potentiodynamic anodic polarization curve in 0.1 M citrate solution exhibits four anodic peaks A1, A2, A3 and A4 prior to the oxygen evolution reaction. Addition of Cl − ions to the solution enhances the four peaks currents, specially A3, which is followed by pitting corrosion. The negative going scans of the cyclic voltammograms show two anodic reactivation peaks A5 and A6 and one cathodic plateau P1. A diffusion controlled process in the potential range of A1, A2 and P1 was detected by RDE experiments. The potentiostatic current time transients, at different concentrations of NaCl and applied potentials E a > A3, were studied. The pit nucleation rate ( t i −1) is found to increase with increasing the concentration of NaCl and the applied anodic potential. The impedance spectra exhibit four different behaviours depending on the potential range used. They were fitted with a single time constant circuit at E a < −700 mV. However, at −700 mV < E a < −480 mV, they were fitted with a circuit with two time constants. At E a > −480 mV, the second semicircle is replaced by negative polarization resistance which is disappeared at E a > −300 mV. The electrode impedance was found to decrease with the applied potential.

Nucleation and diffusion-controlled growth of electroactive centers: Reduction of protons during cobalt electrodeposition

A theory is presented describing, for the first time, the temporal evolution of the fractional surface area, S( t), of 3D non-interacting nuclei growing at a rate limited by diffusion of electrodepositing ions onto substrates of a different nature. Likewise, an equation has been derived describing the potentiostatic current–time transients arising from the formation and growth of such nuclei with redox reactions occurring simultaneously on their surfaces. An equation is also proposed to describe the current due to redox reactions taking place on the surface of interacting growing nuclei. The latter is used to describe the experimental current transients recorded during nucleation and growth of cobalt at applied potentials where the proton reduction reaction occurs simultaneously with the electrocrystallization process.

Electrodeposition of Platinum on Highly Oriented Pyrolytic Graphite. Part I: Electrochemical Characterization

The electrochemical deposition of Pt on highly oriented pyrolytic graphite (HOPG) from H2PtCl6 solutions was investigated by cyclic voltammetry and chronoamperometry. The effects of deposition overpotential, H2PtCl6 concentration, supporting electrolyte, and anion additions on the deposition process were evaluated. Addition of chloride inhibits Pt deposition due to adsorption on the substrate and blocking of reduction sites, while SO4(2-) and ClO4- slightly promote Pt reduction. By comparing potentiostatic current-time transients with the Scharifker-Hills model, a transition from progressive to instantaneous nucleation was observed when increasing the deposition overpotential. Following addition of chloride anions the fit of experimental transients with the instantaneous nucleation mode improves, while the addition of SO4(2-) induces only small changes. Chloride anions strongly inhibit the reduction process, which is shifted in the cathodic direction. The above results indicate that the most appropriate conditions for growing Pt nanoparticles on HOPG with narrow size distribution are to use an H2PtCl6 solution with HCl as supporting electrolyte and to apply a high cathodic overpotential.

Electrochemical behaviour of polycrystalline silver in 0·5M NaOH containing sulphide ions

The electrochemical behaviour of silver in 0·5M NaOH solution containing different concentrations (0·0005–0·007M) of sodium sulphide was studied using cyclic voltammetry, potentiodynamic, and current transient techniques. The anodic sweep of the voltammogram in NaOH was characterised by the appearance of three anodic peaks A3, A4 and A5 that are related to the formation of AgO−, Ag2O and Ag2O2 on the electrode surface. The presence of Na2S in NaOH solution resulted in the appearance of two additional anodic peaks A1 and A2. These two peaks are related to the formation of Ag2S and S, respectively. The addition of Na2S also increases the heights of the anodic peaks A3, A4 and A5. The increase in the current density of the anodic peaks A3 and A4 is mainly due to surface enlargement resulting from pitting and the precipitation of sulphur on the electrode surface. Also, the large increase in the current density of the anodic peak A5 is due to the formation of the soluble SO2−4 compound. The morphology of the electrode surface was examined by scanning electron microscopy. Characterisation of the corrosion products formed anodically on the electrode surface was undertaken using X-ray diffraction analysis. Potentiostatic current–time transients showed that the formation of Ag2S, S and Ag2O layers involves a nucleation and growth mechanism under diffusion control.

Kinetics of Two-Phase Electrocrystallization Processes : II. Generalized Form of the Transients

In the previous paper of this series the forms of the potentiostatic current-time transients (CTTs) due to the instantaneous nucleation and competitive growth of two crystallographic phases of a deposit were identified. In this paper the patterns of behavior of the CTTs over the whole range of nucleation rates, from the lower to the upper limit, that is, from the so-called progressive to the instantaneous limit of nucleation rates, are examined. It is found that the forms of the CTTs remain essentially the same for all rates of nucleation, apart from the expected kinetic shifts and the dependency of current on the deposition time in the early stages. An equation for the slope of the grain boundaries between the two phases is derived. It is shown that grain boundaries between the two phases are a function only of their relative rates of growth and are independent of their nucleation rates. © 2004 The Electrochemical Society. All rights reserved.

Nucleation and growth mechanism for the electropolymerization of aniline in trifluoroacetic acid/lithium perchlorate/propylene carbonate medium

In the present work, the nucleation and growth mechanism for the electropolymerization of aniline in propylene carbonate medium containing 0.06 M trifluoroacetic acid and 0.05 M lithium perchlorate was investigated at different potentials on highly oriented pyrolytic graphite (HOPG) by potentiostatic current-time transients (i-t) and atomic force microscopic (AFM) measurements. The electrochemical data fitted with the theoretical curves for nucleation and growth suggest that the electropolymerization of aniline consists of progressive nucleation followed by 3D growth at an early stage and layer-by-layer growth in subsequent periods. The results obtained from transient analysis were in good agreement with the results of the AFM analysis. In our previous studies with aqueous solutions, we observed only progressive nucleation followed by a 3D growth mechanism for the electropolymerization of aniline in a higher potential range, 1.5–2.0 V vs. Ag/AgCl. Hence, the results obtained from the present work indicate that the nucleation and growth mechanism depends on the medium.

Anodic behaviour of arsenopyrite and cathodic reduction of ferrate(VI) and oxygen in alkaline solutions

This paper presents the results of an electrochemical study of the anodic characteristics of arsenopyrite in strongly alkaline solutions and of the cathodic reduction of ferrate(VI) and of dissolved oxygen at an arsenopyrite surface at potentials which are relevant to the oxidation reactions. Cyclic voltammetry at both arsenopyrite disc and arsenopyrite disc/platinum ring electrodes has shown that arsenic(III) is the main product of the anodic process at potentials in the region of the rest potential during oxidation by either ferrate(VI) or oxygen. Evidence for partial passivation of both the anodic and cathodic reactions has been obtained from potentiostatic current–time transients. The initial stage of oxidation by ferrate(VI) has been shown to be mass-transport controlled and this is also true of the oxidation by oxygen in dilute solutions of sodium hydroxide.