Mass transport and effective diffusion coefficient in the reduction of hydrogen ions from aqueous sulfuric acid solutions: Numerical modeling

This work presents results of the numerical solution to a system of equations of material balance and the movement of particles in solution under the influence of the forces of diffusion, migration, and convection, which describe the process of mass transport during the reduction of hydrogen ions at a rotating disk electrode from aqueous sulfuric acid solutions with and without excess supporting electrolyte. Results of the calculations show that the diffusion kinetics of hydrogen ion reduction can be observed only with measurements in dilute (≤10^?3 M) sulfuric acid solutions with an excess of indifferent supporting electrolyte. For more acidic solutions it is necessary to take into account the simultaneous diffusion of hydrogen and bisulfate ions. In the study of the regularities of hydrogen ion reduction in sulfuric acid solutions with a sulfate supporting electrolyte, it is necessary to take into account that with excess supporting electrolyte, the limiting current of hydrogen reduction is caused solely by the diffusion of bisulfate ions, but for small concentration ratios of the supporting electrolyte to acid, the influence of migration effects is significant.