Low-energy consumption, free-form capacitive deionization through nanostructured networks

Capacitive Deionization (CDI) is a non-energy intensive water treatment technology. To harness the enormous potential of CDI requires improving performance, while offering industrially feasible solutions. Following this idea, the replacement of costly metallic components has been proposed as a mean of limiting corrosion problems. This work explores the use of nanostructured hybrid networks to enable free-form and metal-free CDI devices. The strategy consists of producing interpenetrated networks of highly conductive flexible carbon nanotube (CNT) fibre fabrics and nanostructured metal oxides, γAl₂O₃ and TiO₂, through ultrasound-assisted nanoparticle infiltration and sintering. In the resulting hybrids, a uniform distribution of porous metal oxide is firmly attached to the nanocarbon network while the flexibility, high conductivity and low-dimensional properties of the CNTs are preserved. These electrodes present a high porosity (105–118 m² g⁻¹), notably low electrical (<0,1 kΩ cm²) and low charge transfer resistance (4 Ω), thus enabling the infiltration of aqueous electrolytes and serving as current collector. In this work we built a large asymmetrical cylindrical CDI device solely made of these electrodes and conventional plastics. The cell provides, high average salt adsorption rates of 1.16 mg·g⁻¹_AM·min⁻¹ (0.23 mg·g⁻¹_CDIunit·min⁻¹), low energy consumption (0.18 W h·g_salt⁻¹) and stable electrochemical performance above 50 cycles for brackish water desalination.