Analysis of flow-electrode capacitive deionization: performance assessment of voltage-driven, current-driven, and hybrid control strategies

Flow electrode capacitive deionization (FCDI) is an advanced electrochemical technique for water desalination, offering significant energy efficiency, which is increasingly vital in the context of the growing global scarcity of freshwater resources. This study investigates the performance of three operational modes-constant voltage (CV), constant current (CC), and hybrid CV-CC-in FCDI systems. The results show that the CC mode excels in charge efficiency and ion removal capacity, primarily due to its constant current operation that minimizes energy consumption. In contrast, the CV mode enables faster ion adsorption due to its higher applied voltage, facilitating quicker desalination. The hybrid CV-CC mode integrates the strengths of both CV and CC modes, achieving a 25 % increase in salt adsorption capacity compared to the CC mode, while reducing energy consumption by 24-29 % relative to the CV mode. These findings demonstrate the potential of the hybrid operational strategy in optimizing the performance of FCDI systems, offering a promising approach for more energy-efficient and costeffective water desalination. This work uniquely provides a comparative assessment of CV, CC, and hybrid CV-CC operational modes in FCDI and introduces tortuous-path spacers to enhance mass transfer, offering new insights into optimizing FCDI systems for practical desalination applications.