One of the most prominent and highly valued characteristics of the electrically-driven flow-electrode deionization (e-FCDI) unit, such as those shown in Figs. 1(a-b), is its success in harnessing two processes: electrodialysis and continuous flowable-electrode’s ions trapping and subsequent electrode regeneration. This has resulted in a wide range of technological applications, including desalination, energy storage, scale control, nutrient removal and recovery, pollutant management, heavy metal treatment, and water softening.
Essential components of such an e-FCDI unit are the two ion-exchange membranes (IEMs), each of which is a polymer matrix with specifically-designed pores, channels, or pathways that allow the migration of ions and water molecules. Most importantly, this matrix contains immobile charged functional groups attached to the polymer chains, which selectively attract counter-ions and repels co-ions through electrostatic forces.