The key difference between concentration polarization and kinetic polarization is that concentration polarization comes from the changes in the concentration of the electrolyte, whereas kinetic polarization is the change in static permittivity.
Concentration polarization and kinetic polarization can be described as the contributions to the overpotential of a system. In both these, overpotential is required for the reaction and for the electron transfer across the electrode-electrolyte interphase.
CONTENTS
1. Overview and Key Difference
2. What is Concentration Polarization
3. What is Kinetic Polarization
4. Concentration Polarization vs Kinetic Polarization in Tabular Form
5. Summary – Concentration Polarization vs Kinetic Polarization
What is Concentration Polarization?
Concentration polarization is the part of the polarization of an electrolytic cell that results from changes in the electrolyte concentration that is caused by the passage of current through the electrode/solution interface. We use this term in fields such as electrochemistry and membrane science.
In this context, we can understand the term polarization as the shift of the electrochemical potential difference across the cell from the equilibrium value we obtain for this system. Therefore, the term is equivalent to concentration overpotential.
When there is a chemical species that participates in an electrochemical electrode reaction having a short supply, we can observe a decrease in the concentration of this species at the surface, which also causes diffusion. We can add diffusion to the migration transport towards the surface to maintain the balance of consumption and to deliver the species.
Moreover, we can observe that the concentration polarization leads to an increase in salt leakage through the membrane and increases the probability of scale/fouling development. Therefore, we can also observe that the selectivity of separation and the lifetime of the membrane lifetime deteriorates.
Figure 01: Concentration Polarization
Figure 1 shows the fluxes and concentration profiles in a particular membrane with its surrounding solution. Figure (a) shows the application of a driving force to a system at the initial state of equilibrium. Here, the flux of the selectively permeating species in the membrane is larger than the flux of it in the solution. Figure (b) shows concentrations that give rise to diffusion transport which in turn increases the total flux in the solution, decreasing the flux in the membrane.
What is Kinetic Polarization?
Kinetic polarization can be described as the change of the static permittivity of the solution with respect to that of the pure solvent. An important term regarding kinetic polarization is the kinetic polarization deficiency, which refers to the reduction in the static permittivity of the solution in comparison to that of the pure solvent. Usually, the decrement of this factor is proportional to the product of the dielectric relaxation time of the solvent and the low frequency-conductivity of the solution.
Kinetic polarization is a condition in which the current is limited by the rate at which electrons transfer between the electrode surfaces and the reactants in the solution.
What is the Difference Between Concentration Polarization and Kinetic Polarization?
Concentration polarization and kinetic polarization can be described as the contributions to the overpotential of a system. The key difference between concentration polarization and kinetic polarization is that concentration polarization comes from the changes in the concentration of the electrolyte, whereas kinetic polarization is the change in static permittivity.
Summary – Concentration Polarization vs Kinetic Polarization
Concentration polarization is the part of the polarization of an electrolytic cell that results from changes in the electrolyte concentration caused by the passage of current through the electrode/solution interface. Kinetic polarization is the change of the static permittivity of the solution with respect to the pure solvent concerning. The key difference between concentration polarization and kinetic polarization is that concentration polarization is a result of the changes in the concentration of the electrolyte, whereas kinetic polarization is the change in static permittivity.
Reference:
1. “Concentration Polarization.” An Overview | ScienceDirect Topics.
2. “Concentration Polarization in Pressure Driven Processes.” Synder Filtration.
Image Courtesy:
1. “Fig1 Concentration polarization” By Erar1 – Own work (CC BY-SA 3.0) via Commons Wikimedia