A device for enabling controlled movement of ions between a first ion-containing fluid and second ion-containing fluid comprises at least one cationic exchange membrane positioned between the first and second ion-containing fluids, and at least one anionic exchange membrane in parallel with the at least one cationic exchange membrane positioned between the first and second ion-containing fluids. The one or more of the at least one cationic exchange membrane and the at least one anionic exchange membrane is a membrane electrode assembly comprising an ion exchange membrane, and one or more permeable electrodes embedded within the ionic exchange membrane. The number of cationic exchange membranes and the number of anionic exchange membranes is the same, and the ions move through the membrane electrode assembly in response to a variable capacitive charge.