NUMERICAL STEADY-STATE ANALYSIS OF CURRENT-DENSITY DISTRIBUTIONS IN AXISYMMETRICAL SYSTEMS FOR MULTIION ELECTROLYTES - APPLICATION TO THE ROTATING-DISC ELECTRODE

The multidimensional upwinding method (MDUM) is used for the numerical calculation of concentration, potential and current density distribut ions at a rotating disc electrode controlled by diffusion, convection, migration and homogeneous reactions of multiple ions. MDUM, previousl y applied for two-dimensional applications, is now extended to axisymm etrical problems. The electrolyte solutions are supposed to be dilute, at steady state and at a constant temperature. Numerical calculations are performed for two electrochemical systems. In the first system, s ilver is reduced from a nitrate + thiosulphate solution. This system i s controlled by diffusion, convection and a chemical-electrochemical r eaction, while migration has a minor influence. In the second system, copper is reduced from a copper sulphate + sulphuric acid solution. Si nce the amount of sulphuric acid is not excessive, migration has a sig nificant influence on the current density distribution at the electrod e. For the copper system, numerical data obtained from MDUM are compar ed with both experimental results and numerical data from the literatu re and are found to be in very good agreement. MDUM provides reliable results for both systems without making any simplifications of the gov erning transport equations for dilute solutions and with a reasonable computational effort.