In the present study, a novel reverse electrodialysis (RED) stack with ultrathin lab-made pore-filling membranes and a high-open-area spacer was proposed to enhance the gross power density. The proposed stack had much lower internal resistance than a typical RED stack at optimum flow rates of seawater and river water. Therefore, a gross power density of 2.4 W m⁻² was achieved.

Capacitive deionization (CDI) using a flow-electrode primarily composed of porous materials and an aqueous electrolyte, exhibits continuous deionization and a high desalting efficiency. The development of flow-electrodes with high capacitance and low resistance is essential for achieving an efficient flow-electrode capacitive deionization (FCDI) system with low energy consumption. For this purpose, studies on conductive additives (CAs) that do not clog the flow-channel must be conducted. Here, we evaluated the desalting performance of flow-electrodes with spherical and plate-type conductive additives having sizes between 1 and 10 μm and possessing powder conductivities similar to or higher than nano-sized carbon black, which is often used as the CA in solid fixed electrodes in conventional CDI systems. We confirmed that plate-shaped CAs reduced resistance near the pores and enhanced the desalting performance of the flow-electrodes in FCDI systems. The positive effect of such plate-shaped CAs appears to originate from efficient charge percolation between the ACs via the electrical conductive direction of the graphite and the alignment of the exposed graphite edges to the pumping direction of the flow-electrode. Finally, we verified that the flow-electrode with the newly discovered micro-sized CA could be operated without clogging the flow-channel in FCDI and showed an improved desalting performance of around 1.5 times compared the flow-electrode without the micro-sized CA for extended periods of time.