V. V. Kondrat'ev

Charge Transfer in Iron and Cobalt Hexacyanoferrate Films: Effect of the Film Thickness and the Counterion Nature

Charge transfer processes in films of Prussian Blue (PB) and cobalt hexacyanoferrate (CH) are studied by a variety of nonstationary methods and interpreted by modeling the films as binary electrolytes, with allowance for the so-called “saturation” and “short-range-action” effects. Results of a proper treatment of data for relatively thick PB films agree, to a first approximation, with the interpretation. However, a more careful analysis of the data and the results for thinner PB and CH films call for refining the model and accounting for actual structural features, such as microcrystalline and, consequently, porous character of the films.

Electrochemical Impedance Spectra of Poly(3-octylthiophene) Films

Charge transfer in poly(3-octylthiophene) films in 0.05–0.5 M LiClO4 solutions in acetonitrile is studied by an electrochemical impedance method. The resistance to charge transfer Rct and the capacitance of the electrical double layer Cdl are calculated from the high-frequency semicircle and referred to the film/electrolyte interface. The low-frequency capacitance Clf and effective diffusion coefficient Def are determined by analyzing the region of medium and low frequencies. The discrepancies between potential dependences of Clf and Def derived experimentally and calculated within a simple model for a redox film are analyzed. The assumption is made that additional factors, such as a macroporous character of the films and the change in their properties during oxidation, which results from the film swelling, the change in the film volume and the solvation character, should be taken into account.

Electrochemical Behavior of Polythiophene Films: Effect of Electrolyte Concentration and the Nature of the Alkyl Substituent

The electrochemical behavior of poly(3-methylthiophene) and poly(3-octylthiophene) films in solutions of 0.05–0.5 M LiClO4 in acetonitrile is studied using cyclic voltammetry and chronoamperometry. An analysis of data on the current relaxation following a film perturbation by a pulsed small voltage reveals the presence of two constituents of the current relaxation for either polymer, each constituent exponentially depending on the time. Effect of the electrode potential and electrolyte concentration on the current relaxation parameters are studied. Results of additional studies of poly(3-methylthiophene) films by a faradaic impedance method conform to the chronoamperometry data and permit a more reliable interpretation of them.

Cyclic Voltammetry and the Impedance of Electrodes Modified by Indium(III) Hexacyanoferrate Films

The results of studying indium(III) hexacyanoferrate films by the cyclic voltammetry and faradaic impedance methods are presented. It is shown that the synthesis from solutions with different contents of potassium salts leads to the appearance of films with different electrochemical properties. The impedance spectra exhibit semicircles corresponding to the Randles circuit and portions of the Warburg dependence. Parameters of the equivalent circuit corresponding to the obtained spectra are determined.

Double-layer effects in the electroreduction of cobalt(III) trioxalate complexes to cobalt(0) atoms on a dropping mercury electrode

A polarographic investigation of solutions containing trioxalate complexes of Co(III) reveals that the overall electrode process Co(III) → Co(0) is accompanied by slow formation of ionic associates between aquacomplexes of Co(II) and trioxalate complexes of Co(III). Use of a relatively high concentration of oxalate ions (0.001 M) quells this association. Under these conditions, it is possible to divide the measured current into two constituents related to the primary electroreduction Co(III) → Co(II) and the subsequent process Co(II) → Co(0). The earlier data on the rate constant and apparent transfer coefficient for the process Co(II) → Co(0) are used for calculating corrected Tafel plots for the electrode reaction Co(III) → Co(II). The plots are practically linear and independent of the concentration of the supporting-electrolyte cation in a wide range of potential drops (∼1 V) across the dense layer. A theoretically expected parallel shift of the plots is observed in solutions with a variable concentration of discharging species. This observation and similar data obtained for a mixed potassium–sodium supporting electrolyte bear testimony to good agreement between the obtained results and the theory.

Impedance of indium(III) hexacyanoferrate films: Effect of the supporting-electrolyte cation

Films of indium(III) hexacyanoferrate are studied in nitrate solutions of lithium, sodium, potassium, and ammonium using cyclic voltammetry and faradaic impedance. Effect of the supporting-electrolyte cation on parameters of the equivalent circuit corresponding to the impedance spectra is analyzed. The charge transport at the electrode/film interface is shown to be slow. The cation bonding in a film is discussed.

Electrochemical Properties of Poly-3-methylthiophene Films: A Cyclic Voltammetry and Chronoamperometry Study

The charge transfer in poly-3-methylthiophene films in 0.05–0.5 M LiClO4 solutions in acetonitrile is studied by cyclic voltammetry and chronoamperometry. An analysis of data on the current relaxation following a film perturbation by a low-voltage pulse reveals two constituents of the current relaxation, both exponentially dependent on time. Dependence of parameters of the empirical equation derived for the current relaxation on experimental variables is studied.

Effect of the formation of a charged intermediate on the electroreduction of cobalt(III) trioxalate complexes to cobalt(0) atoms

Kinetic relationships for the recharge of a cobalt(III) trioxalate complex on a mercury electrode are derived for electrode potentials of 0 to –1.5 V vs. point of zero charge (PZC) of mercury. This wide range includes high negative potentials at which the recharge of Co(C2O4)33– and discharge of Co2+ occur simultaneously. The contribution of the reaction Co(II)/Co(0) (whose kinetic parameters are known) into the overall reduction of Co(C2O4)33– to metallic cobalt is calculated. Migration fluxes of species present in solution are shown to be insignificant; hence, these can be neglected in the calculations. Relationships, which permit the determination of a partial polarization curve for the Co(III)/Co(II) recharge from the overall rate of the Co(III)/Co(0) process, are found. A quantitative evidence for the appearance of a secondary current drop at potentials near –0.7 V vs. PZC is obtained. The drop is caused by variations in the outer Helmholtz plane potential because of the commence of discharge of Co2+.