Carbon nanotubes/activated carbon hybrid as a high-performance suspension electrode for the electrochemical desalination of wastewater

In this study, we employed carbon nanotubes (CNTs) to improve the performance of flow-electrode capacitive deionization (FCDI) for wastewater desalination in isolated closed-cycle (ICC) mode. The effects of CNTs loading and initial salt concentration on FCDI desalination were evaluated with energetic performance analysis. FCDI was carried out for the desalination with real wastewater for technology demonstration. The addition of CNTs significantly improved the average salt removal rate (ASRR), associated with a decrease in the flow-electrode flowability. FCDI with 0.25 wt% CNTs had an ASRR of 1.59 μmol/cm2–min, which was 1.7-fold higher than that without CNTs. This was attributed to the bridging effect of CNTs for more rapid charge transfer. Increasing the initial salt concentration from 0.05 to 0.30 M led to a higher ASRR, resulting from a reduction in the electrical resistance in the cell. After further increasing the salt concentration to 0.50 M, the charge efficiency was relatively decreased due to co-ion leakage. Notably, FCDI for the desalination of real saline wastewater achieved a high decrease in conductivity (94%), a high charge efficiency (>99%), and low energy consumption (0.034 kWh/mol). Our results demonstrated that adding CNTs is a feasible approach to achieve high-performance FCDI for sustainable wastewater desalination.