Analysis of the theoretical current-voltage characteristic of non-stationary transport in the cross-section of the desalination channel

Abstract

In practice, the current-voltage characteristic (CVC) is the most important characteristic of transport in electromembrane systems, since it is using CVC that the concept of limiting current is introduced, various modes of operation of electromembrane systems are analyzed, and their efficiency is evaluated. At present, experimental CVC methods of Fourier analysis, wavelet analysis, and dynamical systems are well studied. At the same time, the study of theoretical CVC is not sufficiently developed. Previously, we derived a formula for calculating the CVC of a non-stationary 1:1 transfer of an electrolyte in the cross-section of the desalination channel, which includes an anion-exchange (AEM) and cation-exchange (CEM) membranes, and establishing the fundamental laws of changes in CVC over time. The simulation is based on the NernstPlanck-Poisson equations. In this paper, we analyze this formula and identify the fundamental laws of the CVC of non-stationary 1:1 transfer of the electrolyte in the cross-section of the desalination channel. It is shown that in the prelimiting mode, the migration current and the diffusion current give approximately the same contribution to the total current, and in the overlimiting mode, the main contribution is given by the migration current, the value of the displacement current does not depend on time and is proportional to the sweep speed. It is found that the average conduction current is many times greater than the displacement current, starting from a few seconds. The results obtained allow to construct and analyze the CVC for the cross-section of the desalination channel.

Influence of Space Charge Breakdown on the Performance of Electromembrane Systems

“…Thus, in order to increase the performance of electromembrane systems, it is necessary to apply extreme current modes that will not lead to a breakdown of the spatial charge. Such modes can be determined using basic electrical circuits and a breakdown indicator [5,6]. It is necessary to stop the electrodialysis process when signs of a breakdown of the spatial charge appear.…”

“…This leads to a decrease in the rate of electro-convection and mass transfer [3], which is the reason for the decrease in the productivity of electromembrane systems. Therefore, in order to prevent a breakdown and prevent overspending of electricity, the authors in [5,6] proposed basic electrical circuits to determine the moment of the beginning of the breakdown and determined that the indicator of the breakdown is the bias current. The current-voltage characteristic is an efficiency criterion when using mathematical modeling to theoretically assess the effect of phenomena occurring in electromembrane systems on the transport of salt ions.…”

“…The current-voltage characteristic is an efficiency criterion when using mathematical modeling to theoretically assess the effect of phenomena occurring in electromembrane systems on the transport of salt ions. The current-voltage curve shows how mass transfer (the level of desalination of the solution) takes place at a given potential jump [6]. This level is determined by the current in the system due to the flow of salt ions, i.e.…”