Effect of mass transfer on the current distribution in monopolar and bipolar electrochemical reactors with a gas-evolving electrode

Abstract

The current distribution in an electrochemical reactor with vertical parallel-plate electrodes was experimentally determined. The research was performed with monopolar and bipolar electrodes. The reactor has a gas-evolving electrode and at the counter electrode an electrochemical reaction with combined diffusion and charge-transfer kinetic control, takes place. Therefore the kinetics at the counter electrode are influenced by the bubble-induced convection and by the forced convection of the electrolyte. These reactors are found in many electrochemical processes, for example, electrowinning of metals and electrosynthesis. The test reactions were hydrogen evolution at the cathode and the anodic oxidation of sulphite to sulphate from basic solutions. The current distribution shows a minimum at a distance of approximately six times the equivalent diameter of the reactor from the inlet region. This minimum is a consequence of the interaction between forced convection and the bubble-induced convection, which shifts the mass transfer coefficient of the anodic reaction along the reactor. The effects of the total current, the volumetric electrolyte flow rate and the metal phase resistance on the current distribution are also analysed. The experimental current distribution data are compared with theoretical expectations and good agreement is found.