Effect of complex formation on the mass transfer during anodic dissolution of rotating disk electrode

The effect of complexation on the mass transfer during the anodic dissolution of metal rotating disk electrode involving anions of electrolyte with the formation of stable and unstable metal-anion complexes is theoretically studied. The unstable complexes can decompose with the formation of anions, which can be involved in the electrochemical reaction, i.e. the catalytic mechanism of anodic metal dissolution is realized. The developed mathematical model enables us to solve numerically the problem without using the approximations of the Nernst diffusion layer, equal diffusion coefficients of all solution components, and the condition of equilibrium complexation reaction. For several special cases (solution within the model of the Nernst diffusion layer, equal ionic diffusion coefficients), the analytical solution of the problem was compared with the numerical one. The conditions for the limiting current of anodic dissolution are determined. The role of convection and migration of solution components is revealed. The factors that have the strongest effect on the efficiency of the catalytic mechanism of metal dissolution with the formation of unstable intermediate complex are revealed. (C) 2021 Elsevier Ltd. All rights reserved.