Abstract:
Membrane capacitive deionization (MCDI) offers a low-energy alternative for brackish water treatment, but its performance drops significantly at seawater-level salinities due to membrane resistance and incomplete electrode regeneration. In this work, we introduce a new approach to overcome these limitations by integrating nanopatterned ion-exchange membranes, dilute regeneration strategies, and Prussian blue analogue (PBA)-functionalized electrodes into a flow-by MCDI system.
Nanopatterned membranes with distinct geometries—including hexagonal, octagonal, rectangular, and double-ring—were fabricated using soft lithography. These structures increased the membrane surface area and facilitated ion transport. Among them, hexagonal patterns showed the best performance, offering ~12.5% surface area enhancement and the highest salt removal efficiency.
To further boost performance, electrodes were functionalized with PBA, a redox-active material that improves both salt adsorption and charge transfer. The combined system reduced cell voltage by 500 mV, decreased area-specific resistance by 45 mΩ·cm², and achieved a 423.37 mmol J⁻¹ gain in energy efficiency during desalination of 35,000 ppm NaCl. Additionally, low-salinity (2000 ppm) NaCl and mixed-salt solutions were used for regeneration, enabling ~39% water recovery and maintaining stable electrode behavior across repeated cycles.
This integrated strategy demonstrates how nanoscale membrane engineering and advanced electrode design can significantly enhance MCDI performance for high-salinity water, offering a scalable path toward energy-efficient desalination.