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

TL;DR

This paper presents a novel, low-energy, metal-free capacitive deionization device using nanostructured hybrid networks of carbon nanotubes and metal oxides, achieving high salt removal efficiency and stability.

Contribution

It introduces a new free-form, metal-free CDI electrode design with nanostructured hybrid networks of CNTs and metal oxides, enhancing performance and reducing energy consumption.

Findings

High salt adsorption rate of 1.16 mg/g per minute.

Low energy consumption of 0.18 Wh/g salt.

Stable performance over 50 cycles for brackish water desalination.

Abstract

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, {\gamma}Al2O3 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 ($105 - 118 m^{2} g^{1}$), notably low electrical ($< 0,1 k \Omega cm^{2}$) and low charge transfer resistance (4 {\Omega}), 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 $1.16 mg /g_{AM} min$ ($0.23 mg/g_{CDIunit} min$, low energy consumption ($0.18 Wh/g_{salt}$) and stable electrochemical performance above 50 cycles for brackish water desalination.