Abstract
Bilayer ion-exchange membranes are mainly used for separating single and multiply charged ions. It is well known that in membranes in which the layers have different charges of the ionogenic groups of the matrix, the limiting current decreases, and the water splitting reaction accelerates in comparison with monolayer (isotropic) ion-exchange membranes. We study samples of bilayer ion-exchange membranes with very thin cation-exchange layers deposited on an anion-exchange membrane-substrate in this work. It was revealed that in bilayer membranes, the limiting current’s value is determined by the properties of a thin surface film (modifying layer). A linear regularity of the dependence of the non-equilibrium effective rate constant of the water-splitting reaction on the resistance of the bipolar region, which is valid for both bilayer and bipolar membranes, has been revealed. It is shown that the introduction of the catalyst significantly reduces the water-splitting voltage, but reduces the selectivity of the membrane. It is possible to regulate the fluxes of salt ions and water splitting products (hydrogen and hydroxyl ions) by changing the current density. Such an ability makes it possible to conduct a controlled process of desalting electrolytes with simultaneous pH adjustment.
Highlights
Ion-exchange membranes are nanoporous polymeric materials, the functional properties of which are determined by the laws governing the transport of ions and water in pores with charged walls
In [69], we showed the possibility of synthesizing inorganic catalysts for the water splitting reaction in an asymmetric bipolar membrane
In [30,70], we showed that an ionpolymer catalyst for the reaction of water splitting in the cation-exchange layer of an asymmetric bipolar membrane leads to a significant decrease in the potential drop across the membrane
Summary
Ion-exchange membranes are nanoporous polymeric materials, the functional properties of which are determined by the laws governing the transport of ions and water in pores with charged walls. Ampholytes are substances capable of attaching and donating protons. As a rule, these are acidic residues of weak inorganic (phosphoric, carbonic) or polybasic organic acids containing one or more protons attached to the acid group. These are acidic residues of weak inorganic (phosphoric, carbonic) or polybasic organic acids containing one or more protons attached to the acid group Such ions can change their chemical form and/or charge as a result of a change in the pH of the solution, which means that the composition of the solution will change during the electrodialysis process. The transfer of ions and the properties of ion-exchange membranes in ampholyte solutions differ significantly from those in electrolyte solutions incapable of protonation/deprotonation. The transfer of ampholyte ions in electromembrane systems is Membranes 2020, 10, 346; doi:10.3390/membranes10110346 www.mdpi.com/journal/membranes
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