Hiroaki Matsuda

Linear sweep voltammetry at very small stationary disk electrodes

An expression for linear sweep voltammograms at very small stationary disk electrodes is presented. From numerical calculations theoretical voltammograms are obtained for various values of the dimensionless parameter, p = (nFa2v/RTD)12, where a is the radius of the electrode, v the potential sweep rate and D the diffusion coefficient. The maximum current and the half-maximum potential are evaluated from the voltammograms as functions of p and are expressed by approximate equations with high precision. In order to examine the validity of the equations, an experimental study was made at platinum small disk electrodes (a = 0.025 to 0.10 mm). The experimental voltammograms were in good agreement with the ones theoretically predicted for various values of the sweep rates and for several different radii of the electrodes.

Permselectivity of films prepared by electrochemical oxidation of phenol and amino-aromatic compounds

A selective permeability of the polymers—being derived by electrochemical polymerization from phenol and amino-aromatic compounds—to the various oxidation-reduction species dissolved in the solution was investigated by means of hydrodynamic voltammetry at a rotating disk electrode. Selective permeability was varied with the kind of polymer films coated on the electrode and the kind of ions dissolved in the solution. The films prepared had high permeability to hydrogen ion because of their small size, but inhibited the diffusion of large, highly charged ions (e.g. Fe2+, Eu3+) to the electrode surface. It is demonstrated that platinum electrodes coated with these films can be used as a pH sensor, since they respond selectively to hydrogen ion even in a test solution containing some transition metal ions.

Voltammetry at partially covered electrodes: Part I. Chronopotentiometry and chronoamperometry at model electrodes

Abstract Equations for chronopotentiometry and chronoamperometry at partially covered electrodes have been derived using a model of hexagonal array of cylidrical spaces terminated, at the electrode surface, by concentric active and inactive regions. The boundary value problem was shown to be analogous to that for a charge transfer preceded by a chemical reaction. Experiments with the reduction of ferricyanide on gold model electrodes partially covered with photoresist layer showed excellent agreement with the theory. Application of the equations to estimation of coverage and size of active sites distributed on a electrode surface is discussed.

Limiting diffusion currents in hydrodynamic voltammetry: III. Wall jet electrodes

Summary A new device in hydrodynamic votammetry, termed a “wall jet electrode”, was presented, in which a jet of solution issued from a circular nozzle was allowed to impinge normally on a disk electrode. The construction and electrochemical properties of the wall jet electrode were described. A theoretical equation of the limiting diffusion current at the wall jet electrode was derived. The theoretical predictions for the dependence of the limiting diffusion current upon various experimental variables, i.e. , the bulk concentration of depolarizer, the volume flow rate, the radius of the disk electrode, the diameter of the nozzle, etc., were verified experimentally.

Voltammetry at partially covered electrodes: Part II. Linear potential sweep and cyclic voltammetry

Abstract Effect of inhomogeneity of the electrode surface on the linear potential sweep and cyclic voltammograms is investigated theoretically and experimentally using model electrodes partially covered with photoresist layer. Good agreement between the theoretical and experimental results is obtained.

Voltammetry at microcylinder electrodes: Part I. Linear sweep voltammetry

Abstract An expression for reversible linear sweep voltammograms at stationary microcylinder electrodes is presented. From numerical calculations theoretical voltammograms are obtained for various values of the dimensionless parameter, p=(nFa2v/RTD) 1 2 , where a is the radius of the electrode, v the potential sweep rate and D the diffusion coefficient. The peak current and the peak potential are evaluated from the voltammograms as functions of p and are expressed by approximate equations with high precision. In order to examine the validity of the equations, an experimental study was made at platinum wire micro-electrodes (a=10−10) μm). The experimental voltammograms were in good agreement with the ones predicted theoretically for various values of the sweep rates and for several different radii of the electrodes.

Voltammetry at partially covered electrodes: Part III. Faradaic impedance measurements at model electrodes

Abstract Faradaic, impedances at model electrodes partially covered with a photoresist layer have been studied theoretically and experimentally. Equations for the faradaic impedance are derived based on the theoretical model and approach described in Part I of this series of papers. Experimental data for the hexacyanoferrate system at various model electrodes give excellent agreement, with theoretical predictions for the diffusion impedance behavior, and the applicability of the derived equations to the estimation of the degree of coverage and the size of the active regions is confirmed. Furthermore, the application of such model electrodes to the kinetic study of electrode reactions with high heterogeneous charge transfer rates is suggested.

Apparent diffusion coefficients for electroactive anions in coatings of protonated poly(4-vinylpiridine) on graphite electrodes

Abstract Chronoamperometry, chronocoulometry and chronopotentiometry were applied to measure apparent diffusion coefficients, D app , for Mo(CN) 8 4− , W(CN) 8 4− , Fe(CN) 6 3− and Fe(CN) 6 4− bound electrostatically within coatings of protonated poly(4-vinylpyridine) on graphite electrodes. The relative advantages of the three experimental techniques are discussed. Values of D app for the incorporated anions showed a strong decrease as the anion concentration within the coating increased until a steady value was reached at anion concentrations near 1 M . Some of the factors that may contribute to this behavior are discussed.

Theory of stationary current-potential curves at microdisk electrodes for quasi-reversible and totally irreversible electrode reactions

Abstract An analytical equation for stationary current-potential curves at microdisk electrodes was derived by the Wiener-Hopf method when the electrode reaction is quasi-reversible and totally irreversible. The current-potential curve is a function of the kinetic parameter, , where and are the forward and backward reaction rate constants, respectively; a is the radius of the electrode and D is the diffusion coefficient. The equation consisted of a set of simultaneous equations and was solved numerically. A technique of evaluating the kinetic parameters from experimental current-potential curves is presented which is similar to the method of a polarographic log-plot. The theoretical current-potential curves were compared with that at a hemispherical electrode.

Voltammetry at microcylinder electrodes: Part II. Chronoamperometry

An approximate expression for chronoamperometric curves at stationary microcylinder electrodes is derived in the following form: ia/nFc*D = 1/πθ + 0.422 - 0.0675 log(θ)±0.0058{log(θ)-1.47}2 with θ = Dt/a2, where i is the current density, a the radius of the electrode, c* the bulk concentration, D the diffusion coefficient and ± denotes + for log(θ) ⩾ 1.47 and − for log(θ) <1.47. This equation holds for 0 < θ ⩽ 106 within 1% error. In order to examine the validity of the equation, experimental studies were carried out on carbon fiber (a = 4.2 μm) and platinum wire (a = 10–100 μm) microelectrodes. The chronoamperometric curves measured at times ranging from 40 ms to 8 s were in good agreement with the ones theoretically predicted for several different radii of the electrodes.