Figure 3: Concentration dependence of Na+ mass-transfer coefficients across MK-40 and MK-40/Nf cation-exchange membranes and Cl across MA-40 and MA-40M anion-exchange membranes forming desalination channels in a cell shown in Figure 2 under different potential drops ( ) per cell pair: 2.5 V (a), 4.0 V (b), and 6 V (c). The limiting mass-transfer coefficient for the DC without spacer, , is calculated according to (7); the limiting mass-transfer coefficient for DC with spacer, , is evaluated as described in the text.