Ion-transfer across a membrane in the presence of a preceding slow homogeneous chemical reaction in the diffusion layer

Abstract

The theory of rotating disk electrode developed by Levich is being advanced further and adapted to electromembrane systems with a slow chemical reaction. In terms of the system of Nernst–Plank equations supplemented by the equation of material balance with the source of ions that appear due to the weak-electrolyte dissociation, an attempt is undertaken to describe theoretically the ion electrodiffusion in the diffusion layer of a membrane system complicated by a limiting homogeneous chemical reaction. It is shown that the kinetics in membrane systems with a preceding slow homogeneous chemical reaction has limiting cases in which the process is controlled by either the chemical reaction or electrodiffusion. Depending on the rate constant of dissociation, a kind of mixed kinetics is observed between these two limiting cases. The approximate equation for estimating the limiting kinetic current is derived. The ion concentration profiles and the reaction rate in the diffusion layer are calculated. The effect of the weak electrolyte concentration, the rate constant of dissociation, and the membrane disk rotation rate on the electrochemical characteristics of the system is studied. The theoretical fundamentals for determination of the rate of slow chemical reaction in electromembrane systems by the method of rotating membrane disk are developed.