Improving the feasibility and applicability of flow-electrode capacitive deionization (FCDI): Review of process optimization and energy efficiency

Flow-electrode capacitive deionization (FCDI) is a new electrochemical-based desalination technology that addresses the limitations of preceding CDI processes through the use of a stationary carbon electrode and ion-exchange membrane. As with conventional CDI configurations, non-Faradaic reactions (i.e., ion electrosorption) of the electric double layer model is the principal ion separation mechanism of FCDI. This technology also offers the unique ability for continuous ion/salt separation by circumventing constraints with electrode saturation. This paper reviews recent advances in FCDI, discusses the feasibility and applicability of this technique, and suggests potential niche applications for saline water/wastewater treatment and resource recovery. Additionally, it also critically discusses factors that deteriorate FCDI performance, operating conditions, process energy efficiency, and optimization of the electrode, electrolyte, and cell design. The insights from this review will shed light on directions for future FCDI research and inform the implementation of FCDI technology.