Platinum Rotating Disk Electrode Research Articles

Voltammetric studies of copper(I) and copper(II) with monoamines at the ionic strength of seawater (0.70 M NaClO4)

AbstractThe stabilization of copper(I) by some amines was analyzed by voltammetric methods at the ionic strength of seawater (I = 0.7 M NaClO4). The amines studied were ethylamine, diethylamine, triethylamine, ethanolamine, and 5‐aminopenthanol. Voltammetric methods were used because copper(I) can be produced electrochemically if the ligands in solution stabilize this oxidation state. Differential pulse polarography (DPP) and voltammetry with platinum rotating disk electrodes (RDE) were employed. Because some of the voltammograms were distorted as a result of adsorption problems, adsorption has been studied by ac polarography. For the experimental conditions of negligible adsorption, the stability constants of copper(II) and copper (1) complexes have been determined.

Electrochemical study of the components of Karl Fischer reagent on platinum rotating disk electrode

The electrochemical behaviour of sulphur dioxide and iodide in aqueous and organic solutions at a platinum rde has been studied. For sulphur dioxide the electrodic process is non-reversible and is not controlled by diffusion; the dielectric constant and viscosity of solutions have a direct and reverse effect, respectively, on the limiting current. Iodide, as hydroiodic acid, shows a simple electrodic process which is reversible and controlled by diffusion. Iodide as hydrogen iodide solvated with pyridine shows a process of desorption and disprotonation prior to the oxidation to iodine; the direct and inverse constants, K D = 2.3 × 10 −10 and K A = 5.8 × 10 −7, are calculated. The amperometric study of KF reagent is carried out

Perturbation analysis of catalytic current at a rotating disk electrode

A perturbation method has been developed to analyze the kinetics of a catalytic reaction system where the product of a heterogeneous reaction reacts homogeneously to re-form the reactant. This is used to investigate the kinetics of Fenton's reagent using a platinum rotating disk electrode (RDE). The rate constants of the reaction were found to be 135 M −1 s −1 in the forward direction and 1.5 M −1 s −1 in the backward direction

Tracer diffusion coefficients of I–, I–3, Fe2+and Fe3+at low temperatures

Tracer diffusion coefficients (Di) have been determined by measuring the limiting oxidation or reduction currents at a large platinum rotating-disc electrode. The systems studied at 5 °C were I–, Fe2+ and Fe3+ in an aqueous supporting medium of 0.05 mol dm–3 HClO4 made up to an ionic strength of 0.1 mol dm–3 with NaClO4, and I–3 in 0.05 mol dm–3 HClO4–0.05 mol dm–3 Nal. The last three ions were also studied at 10, 15 and 20 °C. The resulting activation energies were similar to the value expected from the Stokes–Einstein equation. The values of Diη/T, where η is the viscosity of the solution and T the absolute temperature, have been compared with appropriate literature data at 25 °C. The effective hydrodynamic radii of the four ions have been calculated and interpreted in structural terms.

Kinetics of albumin and fibrinogen adsorption onto a rotating disk electrode: Effect of temperature, concentration and material

In a previous paper, the kinetics of albumin adsorption onto a platinum rotating disk electrode polarized at 75 mV/SCE were reported as measured by the variations of the double layer capacitance C d. The adsorption was found to consist of two steps. In the present work, a better characterization of these steps was attempted through a study of the concentration and temperature dependence of the adsorption of albumin and fibrinogen onto platinum and of fibrinogen onto carbon. As expected from the model, each of the two steps of the adsorption process displayed a specific reaction order and activation energy. The reaction orders of the first and second steps were found to be, respectively, 0.36 and 0 for albumin onto platinum, 0.44 and 0 for fibrinogen onto platinum, and 0.81 and 0.61 for fibrinogen onto carbon. In the case of albumin adsorption onto platinum, activation energies of 14.6 and 10.9 kJ mol −1 were calculated for the first and second step, respectively. The area of close contact between the adsorbed protein and the electrode was found to be significantly larger on carbon than platinum. Concerning albumin adsorption onto platinum, the bulk concentration dependence of the variation of C d suggests that proteins adsorb in a different conformation depending on their concentration in solution.

ChemInform Abstract: Electrochemical Oxidation of Ruthenium(IV) at Platinum Rotating Disk Electrodes: Preparation and Characterization of a Tetrameric Ruthenium(4.25) Species.

AbstractA voltammetric study of the anodic oxidation of (Ru4(OH)12)4+ at a Pt rotating disk electrode indicates the formation of a tetrameric Ru(4.25) ions formulated as (Ru4(OH)12)5+, at least in more acidic solutions.

Electrochemical oxidation of ruthenium(IV) at platinum rotating disk electrodes: preparation and characterization of a tetrameric ruthenium(4.25) species

Etude par voltammetrie cyclique de l'oxydation electrochimique dans une solution d'acide perchlorique

Study of the adsorption of albumin on a platinum rotating disk electrode using impedance measurements

The study of the adsorption of albumin on a platinum rotating disk electrode was performed using impedance measurements. The kinetics of the adsorption was investigated by recording, during 15 min after protein addition, the variation with time of the electrochemical double layer capacitance, Cd. The resulting curve was computed and a model of two consecutive reactions occuring at the interface was proposed to describe the adsorption reaction. The corresponding theoretical equation used to fit the data showed five parameters: three capacitance (of the bare surface, of the surface covered with the reversibly adsorbed proteins, and of the surface covered with the irreversibly adsorbed proteins) and two time constants. The influence of the shear rate on these parameters was studied within the range 0–1728s t- and the two time constants, corrected for the mass transfer contribution, showed a shear dependence. Different possibilities were considered for the decrease in capacitance that goes with the adsorbed protein denaturation reaction.

Partitioning of para-phenylenediamines in oil-in-water emulsions

A method to measure distribution coefficients ( P) of electroactive species in situ in turbid oil-in-water emulsions is demonstrated using four p-phenylenediamines (PPD) in oil-in-aqueous-gelatin emulsions of six oils at 40°C. The PPD examined represent a series in β- X-ethyl substitution (4-amino-3-methyl- N-ethyl- N-(β- X-ethyl)aniline) where X = H (2), OH (3), methylsulfonamide (4), and methoxyethyl (5), respectively, for PPD 2–5. The oils examined include di- n-butyl phthalate (DBP), N,N-diethyldodecanamide (DEDA), 1-octanol (OCA), 1-undecanol (UNA), tri- n-hexyl phosphate (THP), and dodecane (DOD). The rotating platinum disk electrode (RPDE) is used as a voltammetric probe of PPD concentration in the aqueous-gelatin phase of the emulsions. Distribution coefficients in macroscopic aqueous/oil systems are also reported, and are illustrated to correlate linearly with values determined in emulsions. The distribution coefficients ( P = C oil C aqueus) for the different PPD decrease in the order 2 > 5 > 3 ≈ 4 for each of the six oils. The largest distribution coefficients are obtained with THP, and the smallest are obtained with DOD. The interface appears to play a significant role in modifying solute distribution in emulsions.

Kinetics of Aqueous Polysulfide Solutions: Part III . Investigation of Homogeneous and Electrode Kinetics by the Rotating Disk Method

The steady‐state current density‐overpotential relationships for cobalt and platinum rotating disk electrodes in aqueous polysulfide electrolyte (1.3M total S2−, 1M S0, and ) were determined over a temperature range of 25°–77°C. A model developed to take into account the rate of the homogeneous dissociation of to as well as a finite heterogeneous electrochemical reaction rate yielded parameters consistent with the results of previous transient experiments (in the low overpotential region). At higher overpotentials in the cathodic region a second cathodic reaction was evident. This second cathodic reaction was less prominent when the current densities were lower (as on Pt electrodes) or when the concentrations were higher (as temperature increased). The addition of 13 mole percent dimethylformamide (DMF) to the aqueous polysulfide solution was found to increase significantly the current density, at a given temperature and overpotential, by increasing the equilibrium concentration of . In the range of overpotentials studied, additions of DMF also caused the first cathodic reaction wave to become much more prominent. Although independent quantitative data are lacking for the DMF‐water mixtures, the use of reasonable values for and allows the quantitative prediction of the observed cathodic behavior.

Electrochemical oxidation of the tris-1,10-phenanthroline iron(II) cation in the presence of sodium dodecylsulfate

The electrodic oxidation of the cationic metal-chelated tris-1,10-phenanthroline iron(II) ion (Fe(ph) 2+ 3) was studied in the presence of the anionic surfactant dodecylsulphate (DS −. Voltammetry at a platinum rotating disk electrode supported the conclusion that the interaction between Fe(ph) 2+ 3 and DS − leads, with increasing surfactant concentration, to: (i) the formation of a neutral electroinactive 1:2 complex ( K 1,2 = 2.5 × 10 6 on the molar scale); (ii) the precipitation of a coacervate phase ( K′ s = [Fe(ph) 2+ 3][DS −] 2 = 6 × 10 −12) and (iii) to the micelle solubilization of the metal chelate at post-cmc concentrations. The analysis of the dependence of the limiting current upon rotation speed can be interpreted on the basis of a charge transfer process preceded by a first-order chemical reaction corresponding to the exit of Fe(ph) 2+ 3 from the micelle. The exit rate constant ( k f) at fixed ionic strength ([Na 2SO 4] = 0.05 mol 1 −1) is independent of DS − concentration in the range 0.02–0.2 mol 1 −1: k f = 2(±1) × 10 3 s −1 1 1 For a diffusion-controlled backward reaction. . The effect of ionic strength (Na 2SO 4 added) and temperature on the limiting current has been investigated.

Investigation of two radical intermediates in the anodic oxidation of 1,4-dihydropyridines by electrochemiluminescence

The chemiluminescence generated in the anodic oxidation of 1,4-dihydropyridines (PyRH) in the presence of 9,10-diphenylanthracene (DPA) or of bis-[1,2,3-trimethyl-1,2-dihydrobenzimidazolyl-(2)]/luminophore systems (B 2/L) was investigated at a rotating platinum disk electrode and by cyclic voltammetry connected with luminescence intensity measurements in a 1:1 acetonitrile + toluene mixture. From the luminescence-potential curves, some new findings on the ECL of dihydropyridines (PyRH) are reported and the cation radicals PyRH π+ are proved to be primary intermediates. The shape and the intensity of the luminescence-potential curves are discussed in terms of structure. If E ox 1 2 (DPA), the system PyRH/DPA appears to be a practical example of the homogeneous redox catalysis of electrochemical reactions.

In situ voltammetric determinations of solute distribution coefficients in emulsions

A method to measure distribution coefficients ( P) of electroactive species in situ in turbid oil-in-water emulsions has been developed and is illustrated for the partitioning of 4-methyl-3-amino- N,N-diethylaniline ( 2) between oil and aqueous phases in an aqueous gelatin/1-undecanol emulsion at 40°C ( P = 55 ± 2). Voltammetry at a rotating platinum disk electrode is used as a probe of 2 concentration in the aqueous gelatin phase. Rheological effects due to the microheterogeneous nature of the emulsion on the limiting currents are quantitatively characterized by the use of 4-amino-3-methyl- N-ethyl- N-(β-sulfoethyl)aniline ( 1), which does not partition measurably into the oil phase.

Oxygen-induced excitability of the belousov-zhabotinskii oscillatory system

The modified Belousov-Zhabotinskii ferroin-catalyzed oscillatory system with the ethyl ester of 3-oxobutanoic acid is described. After an induction period of about 120 s its oscillatory state consisting of four or five oscillations of absorbancy at a wavenumber of 22×10 3 cm −1 can be revived three or four times, if the solution is shaken for 25 s after the oscillatory state has finished. This apparently “mechanical” excitability, which can be observed spectrophotometrically and also polarographically using a rotating platinum disc electrode, proved to be oxygen-induced.

Kinetic studies of the electrocatalytic oxidation of arsenious acid at a platinum rotating disk electrode

The previously proposed EC mechanism for As(III) oxidation in 1 M sulfuric acid was studied by rotating disk voltammetry. The results of the study were consistent with the proposed mechanism that suggested the involvement of platinum oxides in the catalytic oxidation of As(III), as well as in the subsequent deactivation. The maximum turnover rate for As(III) was attained in the potential region of 0.92 V to 1.00 V vs Ag/AgCl, although slow deactivation seemed to be unavoidable, irrespective of the applied potential for As(III) oxidation. As a trade-off between catalysis and deactivation, the optimal potential for As(III) oxidation at a Pt electrode appeared to be in the potential range of 0.85 V to 0.92 V. The rate constants for PtOH formation and the chemical reaction between PtO and As(III) were estimated to be 0.57 ± 0.02 s −1 and (2.2 ± 0.9) × 10 4 M −1 s −1, respectively.

Electrochemical generation of triplet states: Simplified estimation of triplet energies by electrogenerated chemiluminescence based on the anodic cleavage of dimeric dihydroheteroarenes

The chemiluminescence which is generated in the voltammetric oxidation of solutions containing a bis-dihydroheteroarene. P 2, a cation radical precursor. D, and an anion radical precursor. A, in acetonitrile/toluene is investigated at the rotating platinum disc electrode with respect to its use for an estimation of the triplet energies of D or A. In the indirect anodic cleavage of P 2 via the D/D + redox mediator, a strongly reducing intermediate, P , with an oxidation potential between −0.8 and −2.0 V is formed which reduces A to A −. The triplet state 3D or 3A arises from the homogeneous electron transfer between D + and P or A −, and is transformed into the emitting singlet state by triplet-triplet annihilation 2,4,6,2',4',6'-hexamethyl-4,4'-bi4H-pyrane, 1), the bis-[1,4-dihydropyridinyl-(4)] derivatives 2a-2h and bis-[1,2,3-trimethyl-1,2-dihydrobenzimidazolyl-(2)] (3) proved to be suitable as compound P 2. It is shown in some series of experiments that the triplet energy of A, of D, or of triplet quencher. Q. added to the solution can be determined from the luminescence-threshold value of E ox 1/2(D)- E red 1/2(A) or from the dependence of the luminescence intensity on the triplet energy difference E T(A)- E T(Q) or E T(D)- E T(Q). In comparison to the square-wave voltage methods or the rotating ring-disc electrode previously used for this purpose, the method turned out to be simplified from the experimental point of view and to be improved with respect to the lower requirements of the stability of the ion radicals involved.

Electrochemical modeling of the oxidative dehydrogenation of 4H-thiopyrans

The oxidation of substituted 4H-thiopyrans on a rotating platinum disk electrode with a ring in acetonitrile was accomplished for the first time. It was established that the dehydrogenation of both tri- and pentasubstituted thiopyrans proceeds via a scheme involving the successive transfer of an electron, a proton, and an electron (an EPE process); 4H-thiopyrans are oxidized more readily than the corresponding oxygen analogs.

Polarography of 3,4,5-trihydroxybenzoic acid

Polarographic oxidation of 3,4,5-trihydroxybenzoic acid on mercury and platinum electrodes is described. The electrode process is influenced by dissociation of the acid and adsorption of the oxidation products on the electrodes. The anodic peak height in differential pulse polarography is not a linear function of the concentration, which limits the determination of the acid concentration. A linear dependence of the anodic current on the concentration was found on a rotating platinum disc electrode at pH 6.5 or 2.0, which is of advantage determining the acid in physiological solutions and eluates from chromatographic columns.

Anodic deposition of γ-FeOOH layers on inert metal electrodes

The anodic oxidation of Fe 2+ ions in neutral and alkaline solutions was studied by using a gold or platinum rotating disk electrode in the region of limiting currents. The reaction occurs with the quantitative deposition on the base metal of a ferric oxyhydroxide (γ-FeOOH). The effects introduced by the different experimental variables on the limiting currents are reported. The kinetic contributions of the mass transport and of the subsequent reaction steps are individually examined. It is proposed that the reaction scheme involves the coupling of two diffusion steps occurring in solution within the Levich layer and across the thickness of the deposited oxide. These two reaction steps are kinetically connected by the ion transport of Fe 2+ ions across the interfacial potential difference; this latter reaction step is considered to introduce the pH dependence of the overall reaction.

A reconsideration of the kinetic data for the Fe(CN) 63−/Fe(CN) 64− system

The electrode kinetics of the Fe(CN) 6 3−/Fe(CN) 6 4− system was studied using a rotating platinum disc electrode. A significant increase of the standard rate constant was observed for a low depolarizer concentration. This phenomenon was explained in terms of the partial blocking of the electrode surface at higher reactant concentration by poorly soluble species which arise from Fe(CN) 6 3− or Fe(CN) 6 4− under the influence of the electrode field. The results of this paper suggest that the rate constants of the electrode reaction of the Fe(CN) 6 3−/Fe(CN) 6 4− system published so far are too low.