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Flow-electrode capacitive deionization (FCDI) is novel capacitive deionization (CDI) technology that exhibits continuous deionization and a high desalting efficiency. A flow-electrode with high capacitance and low resistance is required for achieving an efficient FCDI system with low energy consumption. For developing high-performance flow-electrode, studies should be conducted considering porous materials, conductive additives, and electrolytes constituting the flow-electrode. Here, we evaluated the desalting performances of flow-electrodes with spherical activated carbon and aqueous electrolytes containing various concentrations of NaCl in the FCDI unit cell for confirming the effect of salt concentration on the electrolyte of a flow-electrode on desalting efficiency. We verified the necessity of a moderate amount of salt in the flow-electrode for compensating for the reduction in the performance of the flow-electrode, attributed to the resistance of water used as the electrolyte. Simultaneously, we confirmed the potential use of salt water with a high salt concentration, such as seawater, as an aqueous electrolyte for the flow-electrode.

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Flow-electrodes have recently been studied for use in capacitive deionization applications because of their continuous and high desalting efficiency. The production capacity of desalinated water in the FCDI system is limited compared to infinite ion capacity of the flow electrodes due to restrictions in the flow-rate of the influent/effluent. Therefore, we designed and fabricated an FCDI stack with 5 unit cells in order to increase the production capacity of desalinated water.Through inlet pressure measurements of the flow-electrodes in the FCDI stack, we confirmed that the flow-electrodes were uniformly segmented from the manifold formed in the FCDI stack into the flow channels of each unit cell. We also confirmed that there was no pressure increase at the flow-electrode in the flow channel caused by the increase in the number of unit cells in the FCDI stack. Also, the FCDI stack showed similar desalting efficiency when compared to that of the FCDI unit cell. On the basis of the results, we verified that the FCDI stack can be successfully used to scale up the desalinated water production capacity of the FCDI system.

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