Theory Of Square-wave Voltammetry Research Articles

Theory of square wave voltammetry of three step electrode reaction

A theory of square wave voltammetry of three step electrode reaction of amalgam forming ions is developed for a thin mercury film electrode. It is assumed that the first and the second electron transfers are kinetically controlled while the third one is reversible and that the intermediates are thermodynamically unstable. The responses to the cathodic and anodic scan directions are analyzed.

Theory of square wave voltammetry of amalgam forming ions at spherical electrodes

A theoretical model of reversible reduction of amalgam forming ion on stationary mercury drop electrode is developed for square wave voltammetry. The dependence of dimensionless net peak current on the dimensionless inverse electrode radius is investigated. This relationship is not linear, but it is a curve with two asymptotes. These results apply to electroanalytical measurements at spherical microelectrodes.

Simulation of square-wave voltammograms of three-electron redox reaction

The theory of square-wave voltammetry of three-electron electrode reaction that consists of one-electron transfer which is followed by the simultaneous transfer of two electrons is developed. If the first step is irreversible and the second one is quasireversible, the extremes of components may be widely separated, resulting in the net response with two peaks. This phenomenon could appear and disappear as the frequency is increased. It is proposed that the particular frequency is measured, at which the two peak currents of the net response are identical. For this critical frequency and the standard signal parameters, the relationship between the standard rate constant of the first step, the transfer coefficient of this step and the difference between standard potentials of two steps is calculated.

Theory of Square-Wave Voltammetry of Two-Step Electrode Reaction Using an Inverse Scan Direction

A theory of square-wave voltammetry of two-step electrode reaction with kinetically controlled electron transfers is developed, and a special case of thermodynamically unstable intermediate is analyzed. If the first reaction step is reversible and the second one is quasireversible, the response splits into two peaks if the scan direction is inverted. The separation of these peaks increases with frequency.

The theory of square wave voltammetry at uniformly accessible hydrodynamic electrodes

An integral equation approach which allows the ready simulation of square wave voltammetry for electrochemically reversible, quasi-reversible and irreversible processes is developed for the case where transport to the electrode occurs across a uniform diffusion layer of finite thickness.

Anodic Stripping Voltammetry at Hydrodynamic Mercury Electrodes. Square Wave Voltammetry: Numerical Theory for Electrochemically Reversible Systems

Numerical simulations exploiting the time-dependent backward implicit method are used to develop the theory of square wave voltammetry as applied to electrochemically reversible processes undergoing anodic stripping at planar mercury electrodes having arbitrary film and diffusion layer thicknesses. Computations made using a time scale distorted to reflect the Cottrellian character of the transient response at short times are found to be extremely efficient when applied to this problem. For the limiting case of semi-infinite diffusion in the solution phase, excellent agreement with existing analytical theory is noted (Kounaves et al. Anal. Chem. 1987, 59, 386). The effects of the pulse frequency are investigated and, in particular, the effect of diffusion layer thickness characterized. Deviations from semi-infinite theory are predicted and rationalized for the case when the magnitude of the latter is comparable to the diffusion length of the solution-phase species during a single pulse width as might occur...

Square-wave voltammetry for ECE mechanisms

The theory of square-wave voltammetry is extended to include the ECE mechanism in which an intermediate chemical step occurs between sequential electrode reactions. Exemplary calculations show how the thermodynamic and kinetic parameters of this mechanism affect the shapes of square-wave voltammograms. The theory is used with a nonlinear least-squares technique to obtain first-order rate constants for the chemical step of the reduction of p-nitrosophenol. This procedure discriminates against several experimental artifacts and does not require the usual separate determination of a normalization current. The rate constants obtained for the intermediate chemical step are 0.46 s{sup {minus}1} at 25{degree}C, 2.40 s{sup {minus}1} at 50{degree}C, and 17.3 s{sup {minus}1} at 80{degree}C (12% uncertainty at 95% confidence) in good agreement with previous studies.

Single drop square wave polarography

The theory of square wave voltammetry for reversible electrode reactions is expanded to include average currents and currents flowing to a growing drop (single drop square wave polarography) using an expanding plane model. Excellent agreement between theory and experiment was found for the reduction of Fe(III), good agreement for the reduction of Cd(II). The expanding plane model proved superior, but not greatly superior to the simpler theory. For the case of average current the effect on the polarogram of the times at which integration is started and stopped is discussed. Integration decreases sensitivity but increases signal-to-noise ratio. The conditions for maximum analytical usefulness are presented.

Theory of square wave voltammetry for kinetic systems

Theory of square wave voltammetry for kinetic systems