Abstract
In a number of recent studies, the authors derived and substantiated a formula for calculating the theoretical current voltage curve (CVC) of electromembrane systems (EMS). This formula was created for the flow cell of desalination of the electrodiaysis apparatus formed by an anion exchange (AEM) and a cation exchange membranes (CEM) in the potentiodynamic mode based on the charge conservation law. In this paper, the formula for the CVC (I –V characteristic) is investigated, its physical meaning, and the contribution of various factors to the CVC are revealed. A new simplified formula is proposed for calculating CVC, stable with respect to rounding errors. The critical values of the current density were determined and the current voltage curve was divided into separate sections. In the article, we showed that for characteristic values of the average flow rate of the electrolyte solution, the initial concentration in all sections of the CVC, the contribution of the convective current is small. The main role belongs to the electromigration (ohmic) current, especially in the overlimiting sections of the current – voltage curve. The contribution of the diffusion current in limiting and underlimiting sections is quite significant, although less than the ohmic current.
Highlights
The current-voltage curve (CVC) is the most important integral characteristic of ion transport in electromembrane systems (EMS)
In a number of recent studies, the authors derived and substantiated a formula for calculating the theoretical current voltage curve (CVC) of electromembrane systems (EMS). This formula was created for the flow cell of desalination of the electrodiaysis apparatus formed by an anion exchange (AEM) and a cation exchange membranes (CEM) in the potentiodynamic mode based on the charge conservation law
A theoretical study of the CVC has not yet been carried out. This is due to the lack of a formula for calculating the CVC, which, on the one hand, adequately reflects the non-stationary and unstable behavior of the I – V characteristics in time, and, on the other hand, it is stable with respect to rounding errors in spatial variables
Summary
The current-voltage curve (CVC) is the most important integral characteristic of ion transport in electromembrane systems (EMS). To analyze the CVC formula, it is necessary to construct a basic electrical diagram of the desalination cell (Fig. 1). In [11], an equation was obtained for the impedance of a three-layer system consisting of an ion-exchange membrane and two adjacent diffusion layers In these works, an attempt was made to use equivalent electrical systems as a model described by electrochemical equations. A flow cell is an open (open) electrical system with unique properties It should be considered as one of the basic and independent elements of the electric circuit, along with resistors, capacitors, etc. To study some properties of the flow channel, simplified circuit diagrams can be built We developed such a circuit diagram and used it to analyze the ratio of currents flowing in a circuit including a desalination channel and formulas necessary to derive the CVC. V AM is a AEM, KM is a CEM, the sign shows the direction of forced convection, the sign shows the directions of the possible movement of anions, the sign shows the directions of the possible movement of cations
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