Investigation of flow rate in symmetric four-channel redox flow desalination system

Flow rate influences overpotentials that cause energy losses in electrochemical and desalination systems, but its effect on redox flow desalination (RFD) of seawater remains unexplored. Here, we report the operational effect of flow rate on seawater desalination through parametric investigation of RFD using ferricyanide/ferrocyanide and elucidate its impact on overpotential using in situ electrochemical impedance spectroscopy. Increasing the flow rates of electrolyte channels reduces electrolyte-membrane interfacial resistances, promoting ionic fluxes across ion-exchange membranes. Intriguingly, we enhance the average salt removal rate by 16.7-fold (48.48 → 811.55 μg cm⁻² min⁻¹) and reduce energy consumption (∼145 → ∼95 kJ mol⁻¹) with only 12.5 mM FeCN, when increasing flow rates of electrolyte channels (5 → 50 mL min⁻¹) at 0.8 V and high-throughput productivity (699.3 L m⁻² h⁻¹). This improvement is due to the electrolyte-membrane interfacial resistance drop (∼25.0 → 1.3 Ω). These findings offer insight on the practical operation and analysis of RFD.