QUASI-ONE-DIMENSIONAL STEADY-STATE ANALYSIS OF MULTIION ELECTROCHEMICAL SYSTEMS AT A ROTATING-DISC ELECTRODE CONTROLLED BY DIFFUSION, MIGRATION, CONVECTION AND HOMOGENEOUS REACTIONS

This article presents a new numerical method for the calculation of co ncentration, potential and current distributions in electrochemical ce lls controlled by diffusion, convection, migration and homogeneous rea ctions of ions. A multi-dimensional upwinding method, originating from the field of fluid dynamics, has been adapted in order to solve this non-linear system, The model developed is able to deal with two-dimens ional electrochemical cells involving multiple ions. The electrolyte s olutions are supposed to be dilute, at steady state and at a constant temperature. Numerical calculations for a quasi-one-dimensional test c ase at a rotating disc electrode are performed. These results are comp ared with both experimental and analytical data, the latter based on a chemical-electrochemical reaction model, for the reduction of silver in a nitrate-thiosulphate solution. The numerical data are found to be in good agreement with the experimental and analytical data. The calc ulation of concentration profiles provides an interesting insight into the degree of dis-equilibrium of a homogeneous reaction in a thin rea ction layer near the electrode.