Convolutive voltammetry with microelectrodes

Abstract

Hemispherical microelectrodes prepared by electroplating of mercury on platinum microelectrodes were used in studies of fast charge transfer processes under convolutive voltammetry conditions. The algorithm used in the convolutive transformation was modified to account for spherical symmetry of diffusion. The sweep rate was varied from 0.1 to 220 V/s. Low sweep rate experiments were used to test the symmetry of the mass transport. It was found that the mass transport to (and inside) the electrodes can be described with good accuracy by the spherical symmetry diffusion. It was shown that the spherical convolution can be used to determine from cyclic voltammetric data the diffusion coefficient of a depolarizer and the number of electrons transfered to (or from) the depolarizer molecule in the electrode process.At high sweep rates the technique was found useful in studies of fast electrode reactions. The technique was tested in the determination of kinetic parameters for Cd2+ reduction in aqueous solutions and p-dicyanobenzene reduction in DMF solutions. In both cases good agreement with values reported in literature was found. Properties of Hg/Pt microelectrodes were also studied using the ac impedance techniques. The ac impedance measurements were carried out at various frequencies (0.1 Hz to 100 kHz) in solutions containing 0.1 to 10−5 M of the supporting electrolyte.