Effect of intermittent convection movements on voltammogram and current transients

Abstract

The influence of intermittent convection movements on electrochemical voltammograms is investigated. When the bath temperature rises to 315 K, the voltammograms exhibit irregular plateaus that differ for independent voltammetry scans, even when the setup is maintained under exactly the same conditions. In this paper, we show that such behavior can be caused by convection movements that develop in the electrolytic cell as a consequence of velocity fluctuations, since no bubbles or regular convective patterns are observed at this temperature. Theoretical current-potential curves for the heterogeneous deposition of metals on silicon electrodes is derived from a model consisting of a one-dimensional balance equation that includes diffusion, convection, and reaction through a time-dependent boundary condition. We obtain the current density associated with the adsorption of particles on the surface and, through this expression, we consider the effect of constant convective velocities on voltammograms. Finally, we examine the effect of random convective movements, described by a Monte Carlo algorithm that takes into account the random temporal fluctuations around a null convective current. The model predicts accentuated fluctuations on the current profiles, especially on the current plateaus that correspond to a stationary current regime. The validity of the theoretical model is checked against experimental data.

Diffusion, reaction and forced convection in electrochemical cells

“…(4), for a fixed diffusion layer thickness d = 0.06 cm, at constant temperature T = 300 K and deposition potential V = À1.2 V. Distinct sets of concentration profiles are generated for three different convective velocities, at distinct times. To generate the points we adopt the values depicted in Table 1 of reference [10]. Fig.…”

“…6 we show four theoretical voltammograms, produced by Eq. (6), using the prescription thoroughly described in references [10][11][12][13]. These voltammograms describe Co deposition on n-silicon electrodes, at temperature T = 300 K and with the potential increasing linearly at a scan rate of 10 mV/s.…”

“…(1) under conditions (2), as derived in reference [10], reads In Eq. (4) h ¼ À vc 2D and k 2 n ¼ np d À Á 2 D are the eigenvalues associated to the spatial differential equation that results from the separation of variables in Eq.…”

“…(3) was introduced and thoroughly discussed in references [10][11][12][13], it describes the reactive properties of the electrode. The definition of all symbols used in Eq.…”

“…Finally the time-dependent boundary condition (2c) determines the evolution of the concentration of ions on the electrified surface. This condition is basically regulated by the magnitude of k, the reduction reaction rate, given by the expression [10][11][12][13].…”