Hydrodynamic Characterization of an Electrochemical Cell with Rotating Disc Electrode: A Three-Dimensional Biphasic Model

Abstract

Electrochemical cells with a rotating disc electrode are the preferred devices to characterize electrochemical reactions because simple analytical expressions can be used to interpret the information obtained from physical experiments. These equations assume that the velocity field in the vicinity of the electrode active face is in accordance with the ideal behavior described by von Kármán. Experimental liquid velocity measurements inside the cell reported in recent works suggest that the actual liquid flow pattern is not fully in accordance with the assumed ideal behavior. In this work, the Computational Fluid Dynamics technique was employed to characterize numerically the flow pattern inside the electrochemical cell. By using a three-dimensional model, symmetric conditions were not imposed. A biphasic system was employed to evaluate the influence of liquid free surface over the flow pattern. Unsteady state numerical simulations were performed using the commercial software Fluent. Multiple electrode rotation speeds and several cell sizes were employed. Contrary to the assumed behavior, it was obtained that the flow pattern inside the electrochemical cell is not symmetric due to the synergetic effect of the cell walls, the submerged electrode side wall and the liquid free surface. This work states that the differences between actual and the ideal flow patterns can be minimized with plain electrode and cell geometrical modifications.

Hydrodynamic Analysis of Electrochemical Cells

“…This result was reproduced numerically through threedimensional numerical simulations (Serre & Bontoux, 2007). The effect of the liquid phase free surface on the flow pattern inside the electrochemical cell with a RDE has been studied recently by Real, et al (Real, et al, 2008), Real-Ramirez, et al (Real-Ramirez, et al, 2010) and Gonzalez, et al (Gonzalez, et al, 2011). These works conducted several three-dimensional unsteady-state numerical simulations using biphasic systems.…”

“…8. Example of the biphasic three-dimensional models employed by Gonzalez, et al (Gonzalez, Real, Hoyos, Miranda, & Cervantes, 2011), Real-Ramirez, et al (Real-Ramirez, Miranda-Tello, Hoyos-Reyes, & Gonzalez-Trejo, 2010) and Real, et al (Real, et al, 2008).…”

“…The biphasic three-dimensional numerical simulations confirm that the asymmetry grade strongly depends on the geometrical configuration of the system. By analyzing the results of several physical and numerical simulations at different electrode rotation speeds and several cell sizes, those works found that there exist a synergetic effect of the cell internal walls, the submerged electrode side wall and the liquid free surface (Real-Ramirez, et al, 2010). Their numerical simulations showed that the asymmetry of the electrochemical cell flow pattern is intensified by the free surface asymmetry, which depends directly on the electrode rotation speed and the electrode submergence depth (Gonzalez, et al, 2011).…”

“…Figures 11 and 12 clearly show that the offset from the center of the electrode of the stagnation point depends strongly on the distance between the electrode active face and the cell bottom wall. Based on the results of their numerical simulations, Real-Ramirez, et al (Real-Ramirez, et al, 2010) stated as rule of thumb that the distance between the electrode active face and the cell bottom wall must be at least three times the electrode external diameter.…”

“…By analyzing the results of biphasic three-dimensional numerical simulations of an electrochemical cell with a cylindrical electrode, several authors found that the submerged electrode side wall along with its right angle shape induces that the liquid velocities in the vicinity of the electrode active face were lower than that predicted with the ideal model (Gonzalez, et al, 2011;Real-Ramirez, et al, 2010). To obtain a liquid velocities field as close as possible to the ideal one, those authors suggest using electrodes with rounded border shape.…”