Enhanced desalination performance utilizing sulfonated carbon nanotube in the flow-electrode capacitive deionization process

The CNT-S is used as the active material in the FCDI cell. It favors the flow-electrode slurry with better dispersible property and suspension stability. What’s more, the CNT-S could also promote good contact between the active material and the current collector by forming the conductive network. [Display omitted] •The sulfonated CNT-S material exhibits good hydrophilicity and suspension stability.•CNT-S flow-electrode displays excellent electrochemical properties.•The CNT-S FCDI cell achieves high salt removal efficiency of 45.8%.•The continuous desalination and desorption processes can be achieved in the CNT-S FCDI cell. The novel sulfonated carbon nanotubes (CNT-S) material was successfully introduced into the flow-electrode capacitive deionization (FCDI) process, which could reduce inter-tube aggregation and promote good contact between the active material and the current collector by forming the conductive network. The physical characteristic and electrochemical tests were carried out to analyze the effects of surface properties of CNT-S on the suspension stability and electrochemical performance of the flow-electrode, respectively. The results indicated that the CNT-S flow-electrode slurry displayed better dispersible property and suspension stability, higher charging capacity and lower ohmic impedance than that of the CNT flow-electrode slurry. Moreover, the desalination performance of the CNT-S flow-electrode was investigated based on the symmetric FCDI cell. For the 2.0 wt% CNT-S flow-electrode, the mean electrosorption rate of 4.85 mg/(g·min) and the salt removal efficiency of 45.8% were achieved in 1.0 g/L NaCl solution, both of which were all about 1.6 times that of the CNT flow-electrode. It was also found that the CNT-S FCDI system coupled with the adsorption and desorption process simultaneously can achieve high electrode regeneration efficiency by controlling the flux ratio of the washing fluid to the feed solution. Therefore, the CNT-S flow-electrode was a promising active material in the FCDI process and displayed prominent advantage in improving the desalination performance of the FCDI cell.