R.I. Tucceri

The effect of pH on the charge transport at redox polymer-modified electrodes: an a.c. impedance study applied to poly(o-aminophenol) film electrodes

Impedance spectroscopy was used to study the effect of solution pH on the electrochemical behavior of poly(o-aminophenol) (POAP) modified electrodes. An a.c. impedance expression was derived on the basis of a model which considers a chemical reaction influencing the dynamics of the charge transport process by electron hopping between redox sites. Experimental impedance spectra of POAP films at different pH values of the bathing electrolyte were fitted by means of this theoretical equation. A pKa value for the proposed protonation reaction could be estimated from the model.

Effect of the bathing electrolyte concentration on the charge transport process at poly(o-aminophenol) modified electrodes. An ac impedance study

The effects of ionic strength and film thickness on the transport properties of poly(o-aminophenol) (POAP) film electrodes were studied by impedance spectroscopy. The dependences of the characteristic impedance quantities (Warburg coefficient, resistance and redox capacitance at low frequency) on these external variables were interpreted on the basis of two models: a transmission line and a modified electron hopping model. Analysis of experimental data by means of the transmission line model allowed us to separate the charge transport process within the film in terms of electronic and ionic contributions represented by the diffusion constants. Dc and Dx, respectively. Application of the electron hopping model only gave an effective diffusion coefficient, Dcff. The diffusion coefficients Dc and Dx, in the first case, and Deff in the second case, depend upon the ionic strength and film thickness. Moreover, Deff is very close to Dc. This proves that charge propagation is dominated by electron transport in this polymer.

Charge transfer in poly(o-toluidine) gold modified electrodes. An EIS study of the reduced state

The impedance response of poly(o-toluidine) (POT) electrochemically grown films was studied in the potential range, 0.0<E<0.35 V, where the polymer is in the insulating state. The electrolytes employed were aqueous solutions of H2SO4 and HClO4 with different concentrations. The predominant impedance parameters in this potential range, the charge transfer resistance, RCT, in parallel with the corresponding double layer capacitance, Cdl, were considered in terms of the applied potential, the polymer film thickness and the nature and concentration of the electrolyte.

Electrochemical deposition and stripping of nickel at a polycrystalline gold film electrode studied by cyclic voltammetry and surface conductance

Adatom and bulk nickel deposition onto gold thin film electrodes from an electrolyte containing KSCN, was studied by simultaneous application of cyclic voltammetry and the surface conductance (SC) technique. The latter is sensitive only to surface impurities, which allows monitoring of the formation of nickel adatoms on the gold film surface. At low adatom coverages nickel deposition fulfils the surface Linde rule for surface impurities. The SC response during bulk nickel deposition shows a small decrease due to the increase of the sample thickness.

Ac stripping voltammetry from mercury film electrodes: Part 1. Theoretical analysis

Abstract An expression is obtained for the alternating stripping current from a continuous mercury film electrode for a linear potential perturbation. Since the ac depends on the mean surface concentrations of the reduced and oxidized states, it is necessary to solve the dc problem for a linear potential sweep. This is done in two ways: (i) by assuming that the linear sweep can be considered as a series of potential steps and applying the equations developed by Osteryoung and Christie; (ii) by applying the rigorous solution proposed by Garcia. The mean surface concentrations were calculated as a function of the electrode thickness l and the applied potential E . The ac response is analyzed as a function of l , E , and the frequency Ω. The results indicate that, at very low l , the ac is a linear function of l and Ω. The peak potential shifts in the negative direction as l decreases. For quasi-reversible processes there is a frequency Ω lim for which the ac is controlled only by charge transfer; Ω lim increases as the thickness decreases.

Determination of the complexation capacity of waters. Measurements on model systems and natural waters employing copper as the titrating ion

The complexation capacity of both model systems and natural waters was investigated by anodic stripping voltammetry (ASV) employing copper as the titrating ion. EDTA, NTA, citrate and humic acids were employed as model systems. Natural waters from the Santiago River were also investigated. In some cases the influence of the electrode rotating speed on the lability of the species involved was investigated. The experimental results were analyzed employing diagnosis criteria proposed by previous workers for lability, complex strength and stability constants.

Determination of the complexation capacity. Electrochemical lability in the absence of excess of ligand

Abstract Some electrochemical lability criteria are established on the basis of the solution of the mass transfer equations for a reversible charge transfer coupled to a previous dissociation reaction of the complex assuming an excess of ligand species. During the course of a titration curve the ratio of the analytical concentration of metal to ligand changes by several orders of magnitude, so these assumptions are not fulfilled near and before the equivalence point. Theoretical titration curves were calculated from the analytical solution of the mass transfer equations obtained in excess of ligand and by solving them numerically without assuming ligand excess. Comparison of the titration curves for the different parameters: electrode rotation speed and complex dissociation constant and rate constants allows the electrochemical lability criteria established on the basis of the analytical solution to be tested. One of the aims of the work is to prevent and discuss an alternative method for obtaining the complexation capacity and the conditional dissociation constant from titration curves.

Ac stripping voltammetry from mercury film electrodes Part 2. Comparison of theoretical and experimental results

Abstract The theory of ac anodic stripping from mercury film electrodes on glassy carbon was tested experimentally. Both dc and ac experiments were carried out at different electrode thicknesses, amalgam concentrations and frequencies. Pb, Cd and Tl were used as analytes. The dc results show quantitative agreement with the de Vries-Van Dalen theory. The results for the ac experiments show reasonable agreement with theory for thickness l > 0.05 μ m under the given experimental conditions. The disagreement found for thinner electrodes is attributed to non-continuity of the film and the influence of spherical diffusion.