Scalable Approach to Highly Efficient and Rapid Capacitive Deionization with CNT-Thread As Electrodes

A scalable route to highly efficient purification of water through capacitive deionization (CDI) is reported using CNT-thread as electrodes. Electro-sorption capacity ( q e ) of 139 mg g –1 and average salt-adsorption rate (ASAR) of 2.78 mg g –1 min –1 achieved here is the highest among all known electrode materials and nonmembrane techniques, indicating efficient and rapid deionization. Such exceptional performance is achieved with feedstock concentrations (≤1000 ppm) where conventional techniques such as reverse osmosis and electrodialysis prove ineffective. Further, both cations (Na +, K +, Mg 2+, and Ca 2+ ) and anions (Cl –, SO 4 2– and NO 3 – ) are removed with equally high efficiency (∼80%). Synergism between electrical conductivity (∼25 S cm –1 ), high specific surface area (∼900 m 2 g –1 ), porosity (0.7 nm, 3 nm) and hydrophilicity (contact angle ∼25°) in CNT-thread electrode enable superior contact with water, rapid formation of extensive electrical double layer and consequently efficient deionization. The tunable capacitance of the device (0.4–120 mF) and its high specific capacitance (∼27.2 F g –1 ) enable exceptional performance across a wide range of saline concentrations (50–1000 ppm). Facile regeneration of the electrode and reusability of the device is achieved for several cycles. The device demonstrated can desalinate water as it trickles down its surface because of gravity, thereby eliminating the requirement of any water pumping system. Finally, its portable adaptability is demonstrated by operating the device with an AA battery.