Automated Impedance Measurements in Electrochemical Cells
Abstract In this paper a system is described for impedance measurements in electrochemical cells, integrated by a fast potentiostat, signal generator, digital transient recorder and a computer interface. The treatment of the signal is made by obtaining the correlation between the response cell signal with the in-phase and in-quadrature signals, as is made in the frequency response analysis systems, but the quadrature component being numerically generated. This allows one to obtain the d.c. first and second harmonic cell responses in a single experiment, as well as the a.c. phase selective response by programming the reference signal phase angle. The results obtained with a dummy cell showed the validity of the procedure since the deviation of the measured results from the theoretical data is low. The C/E curve of the interface 1 M KCI/Hg at 25°C is concordant with that previously reported in the literature. Moreover, the system has been tested with the reduction of Cd(II) ion.
Development of a Spectroelectrochemistry Assembly (SNIFTIRS) Based on a Commercial Spectrophotometer. Test with the Ferrocyanide/Ferricyanide Redox Couple
The development of a spectroelectrochemistry assembly for substractively normalized interfacial FTIR spectroscopy (SNIFTIRS), based on the commercial spectrophotometer Unicam Research Series 1, is presented. The sample chamber has been modified to achieve a vertical orientation of the cell and a special support was constructed for the same purpose. The original path of the IR radiation has been modified by using two black anodized aluminium 30° wedges, both supporting a parabolic mirror. This allows the radiation to reach the working electrode forming 60° with the vertical. The cell holder allows vertical and horizontal displacement of the cell. The electrochemical cell was made of Pyrex glass and permits an easy manipulation even in the sample chamber of the spectrometer, making it unnecessary to open this chamber in the manipulation of either the solution or the electrodes. The working electrode was a polished polycrystalline gold electrode. A computer-based potentiostat was also constructed. To control the system, a set of 16-bits Visual-Basic programs was developed allowing the synchronization between the spectra acquisition and the application of potentials. A variety of sequences of operation can be selected. The system was checked with the ferrocyanide/ferricyanide redox couple, concluding that the system here described is useful to make SNIFTIRS experiments, being versatile enough to design new operational sequences that help improve the knowledge of the electrode processes.
Convolutive voltammetry with microelectrodes
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 a...