Dilute Regeneration‐Driven Membrane Capacitive Deionization of Synthetic Seawater using Nanopatterned Membranes and Prussian Blue Analog Electrodes

Abstract Membrane capacitive deionization (MCDI) offers energy‐efficient seawater desalination but is limited at high salinity by membrane resistance and incomplete electrode regeneration. Nanopatterned ion‐exchange membranes, dilute regeneration protocols, and Prussian blue analog (PBA)‐functionalized electrodes are combined in a flow‐by‐MCDI cell. Nanopatterned ion‐exchange membranes (hexagonal, octagonal, double‐ring, rectangular) enhance interfacial ion transport, with hexagonal geometry delivering ≈12.5% greater surface area and the best performance. PBA‐functionalized electrodes increase salt adsorption and charge‐transfer kinetic rates. The integrated system lowers the area‐specific resistance by 45 Ω cm ² , resulting in a 500 mV reduction in the cell voltage for a current density of 2 mA cm ⁻² for a 35 000 ppm NaCl feed. This improves the energy‐normalized salt adsorption six fold (64–382 mmol J ⁻¹ ). Low salinity (2000 ppm) and mixed‐salt regeneration sustains a ≈39% water recovery and stable performance for at least seven cycles. Overall, combining nanopatterned membranes, which promote confinement‐enhanced ion mobility, and PBA electrodes, which enhance salt adsorption, improved the energy efficiency of MCDI.