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.
The anodic dissolution of molybdenum in alkaline solutions — electrochemical measurements
Abstract The anodic dissolution of molybdenum has been investigated in sodium hydroxide solutions using a rotating disc electrode. Log i — E curves in the potential range −500 mV to +300 mV (vs. 1 M NaOH/Hg/HgO) show a Tafel region followed by a region in which the current varies only slowly with potential. Impedance spectra give evidence for an impedance with one relaxation process and a diffusional impedance. This is considered to be due to the film/solution interface. Current-voltage curves and impedance measurements are discussed in terms of the oxide films present on the electrode surface as determined by X-ray photo-electron spectroscopy measurements. A different type of impedance spectrum is seen as each new molybdenum species is formed.
On-line FFT faradaic admittance measurements application to A.C. cyclic voltammetry
A measurement approach is described and data are presented which demonstrate the ability to effect a.c. cyclic voltammetric measurements with the on-line digital FFT approach to faradaic admittance data acquisition. The equipment utilized enables complete faradaic admittance spectra to be obtained at an effective spectrum acquisition rate of 10 s−1, so that the d.c. potential range encompassed by a typical cyclic wave can be encompassed with adequate resolution in the Edc dimension in ≥6 s, approximately. The instrument features dynamic, computerized measurement and compensation of the non-faradaic ohmic resistance and double-layer capacitance contributions to the acquired total cell admittance. Measurements with quasi-reversible systems yield the expected faradaic admittance and phase angle responses over a quite generous bandwidth. Applications to mercury and platinum electrodes are illustrated.