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Convolutive voltammetry was employed in studies of the kinetics of sulfide ion adsorption at copper amalgam and mercury electrodes. Measurements were carried out for low electrode coverages to minimize the effect of the lateral interaction energy, and the results were extrapolated to zero coverage. In the case of a Cu amalgam electrode (7.4×10−4 mol dm−3 of Cu) kinetic and thermodynamic parameters of the adsorption/desorption process were determined in solutions of different pH (3.6 to 12.8). For pH

Oxidation of ferrocene (Fc) and reduction of p-dicyanobenzene (DCB) were examined by ac-voltammetry in benzene solutions containing tetra-n-hexylammonium perchlorate at a hemispherical (Hg) and a disk (Au) μm-electrode, respectively. The specific conductivity of benzene solutions indicates that the degree of dissociation of the supporting electrolyte is less than 1%. The low concentration of free ions combined with the low dielectric permittivity of the solvent cause large double layer effects evident from the values of the charge transfer coefficients (0.35 and 0.69 for Fc and DCB, respectively). In addition, the low concentration of ions causes problems in measurements of charge transfer kinetics if the concentration of the depolarizer exceeds 0.2 mM. The standard rate constants obtained in benzene solutions (0.22 and 0.15 cm s−1 for Fc and DCB, respectively) are not much different from values observed in common polar solvents. Apparently, in benzene solutions, very weak electrical coupling of the activated state with solvent molecules is compensated by very strong interactions with counter ions and large double layer effects. The experimental results indicate the necessity of taking into account ionic relaxation processes in a theoretical description of interfacial charge transfer dynamics.

The computations described in the paper are based on the Frumkin adsorption isotherm. Variation of the electrosorption valency with potential is taken into account. The rate-determining step can be either diffusion or interfacial kinetics. The kinetics of charge transfer associated with the formation of a chemical bond between an adsorbate and an electrode is described in terms of the Butler-Volmer equation. The effect of lateral interactions between adsorbed molecules and the activated complex is also considered. The presented dependences of the peak width and peak potential on the electrode coverage and the sweep rate allow the determination of various kinetic and thermodynamic parameters of the adsorption process. Computations were carried out for both linear and spherical symmetry of diffusion.

A method for determination of the thermodynamic and kinetic parameters of electrosorption from fast sweep rate cyclic voltammograms was developed and tested using a simulation program. The method was then used for determination of the thioglycol adsorption kinetics on Hg in KOH and H 2 SO 4 aqueous solutions. Cyclic voltammetric experiments were carried out with a hemispherical Hg ultramicroelectrode (5 μm radius) at sweep rates ranging from 1000 to 100 000 V s −1 . The experimental data fit relatively well to a theoretical model based on the Frumkin adsorption isotherm, despite the fact that the current model assumes independence of the electrosorption valency and the interaction parameter of the potential and the electrode coverage, and that it neglects possible reorientation of adsorbed molecules on the surface with a change in electrode coverage and/or potential. It was found that the electrosorption valency for thioglycol in both solutions studied is similar and close to unity; the standard energies of adsorption are 2.93 and −46.6 kJ mol −1 in 1 M H 2 SO 4 and 1 M KOH respectively; the interaction parameters are −3670 J mol −1 (in 1 M H 2 SO 4 ) and 2450 J mol −1 (in 1 M KOH); the rates of adsorption and desorption steps extrapolated to the zero charge potential are k a 0 = 4.7 × 1O 5 s −1 , k d 0 = 9.8 × 10 6 s −1 (in 1 M H 2 SO 4 ) and k a 0 = 1.7 × 10 12 s −1 , k d 0 = 2.12 × 10 4 s −1 (in 1 M KOH). The interaction parameter for the activated complex in both studied solutions is 3000 J mol −1 larger than the corresponding interaction parameter of the product. The results are discussed in terms of participation of protons in the adsorption-desorption process and the effect of potential on the orientation of adsorbed molecules.

In this technique a potential excitation waveform is obtained by a superposition of a small amplitude square-wave modulation on a staircase function. The square-wave cycle is repeated several times (usually 16) at each potential step. The electrode response is sampled at even time intervals 2 n (where n = 2, 3, 4…) times per square-wave cycle, and the fast Fourier transform of the electrode response at each potential step is performed. This allows the electrode admittance to be calculated for various odd harmonic frequencies and plotted as a function of the staircase potential. In addition, the average current at each potential step as well as the even harmonic response generated by non-linearity of the studied system can be obtained from collected data. The admittance data are almost identical with those obtained from traditional ac voltammetric experiments, but the equipment is less expensive and the experiments are run much faster and provide more information. The technique was tested by studying kinetics of Cd 2+ reduction from NH 4 + | NH 3 (aq) buffer on the static mercury electrode. Experimental results were compared with those obtained by digital simulation. Diagrams of electronic circuits used in the experiments are also presented.

Ammonium amalgam formation has been studied at mercury ultramicroelectrodes in various organic solvents and at standard size mercury electrodes in aqueous solution. Numerical simulations were carried out in order to establish the kinetics of the process. Ammonium amalgam is formed via a fast charge-transfer process, but it undergoes a decomposition according to the first-order rate law with a rate constant of about 0.6 s−1. In addition, some NH4+ ions are irreversibly discharged at the electrode surface, presumably to form H2 and NH3. This competing process is affected strongly by the nature of the solvent. Matching of experimental and simulated curves suggests that the diffusion coefficient of NH4 in mercury is about 1.8 × 10−5 cm2 s−1. The standard potential of NH4+(aq)/NH4(Hg) was determined to be −1.723 V/SHE. The absolute chemical potential of ammonium ions in mercury was calculated and compared with that of alkali metal ions.

The methodology for carrying out ac voitammetric measurements with ultramicroelectrodes is discussed. Electron-transfer rate constants for the oxidation of ferrocene (FeCp2) at a Pt ultramicroelectrode and cobaltocene (CoCp2) at Hg, Au and Pt ultramicroelectrodes were measured at frequencies from 2 to 50 kHz. It was shown that the method can provide accurate information about fast interfacial charge-transfer kinetics in organic solvents. The rate of CoCp2 oxidation on Hg or Au electrodes was found to increase with a decrease in the supporting electrolyte concentration, but in the case of the Pt electrode no effect of the supporting electrolyte concentration was observed for oxidation of either CoCp2 or FeCp2. The state of the Pt—solution interface was examined by studying the H+ adsorption—desorption process in aqueous H2SO4 and the double-layer capacitance in nonaqueous media.

Electrodeposition of alkali metals on Hg/Au electrodes from non-aqueous solutions was studied using cyclic voltammetry and chronoamperometry. At temperatures of 20 to − 70°C the formation of bulk intermetallic compounds preceded by nucleation phenomena was observed. Stoichiometry of the solid phases formed under these conditions was determined. At very low temperatures, when the mobility of mercury atoms was restricted, the underpotential deposition of alkali metal ions on solid mercury electrodes was noted. The Gibbs energies of electrosorption are discussed in terms of interactions between alkali metals and mercury.