The Limiting Current of Metal Electrodeposition on Rotating Disk Electrode: The Role of Solution Composition and Transport Properties

The processes of mass transfer in the metal electrodeposition on a rotating disk electrode from the solution containing three sorts of ions (electroactive metal cation and indifferent electrolyte containing inactive cation and anion) are studied theoretically. The Nernst–Planck equations in the approximation of the solution electroneutrality reduced to a dimensionless form, which takes into account the elecrodiffusion and convective transfer of all types of ions, are used as the mathematical model. The numerical solution of the mathematical model is carried out by the finite volume method using a non-uniform grid. As a result of the numerical solution, the distributions of potential and ion concentrations are obtained with taking into account the interaction between the electric and hydrodynamic fields in the solutions with various concentrations of supporting electrolyte at various diffusion coefficients of ions of all sorts. The dependences of the limiting current of metal electrodeposition on the concentration of supporting electrolyte are obtained. When calculating the limiting current density in the absence of convection, the thickness of the Nernst diffusion layer is calculated taking into account the effective diffusion coefficient of the solution with three sorts of ions at various concentrations of supporting electrolyte. Using several examples with various ratios between the diffusion coefficients of the anion and inactive cation of the electrolyte, the error in the limiting current calculated using the Nernst diffusion layer approximation, as compared with the limiting current obtained taking into account the convective transport of ions, is estimated.