Enhanced Water Desalination by Increasing the Electroconductivity of Carbon Powders for High-Performance Flow-Electrode Capacitive Deionization

Flow-electrode capacitive deionization (FCDI) can be improved via enhanced charge transfer by increasing the flow-electrode (FE) conductivity. Since water is the main component of FE (>70%), the key to improving the electroconductivity lies in the properties of carbon materials. In this work, three types of carbon powders, i.e., activated carbon (AC), mesoporous carbon, and carbon nanotubes (CNTs), were employed in FEs to investigate the influence of powder properties on the FCDI performance. The morphology and structure of powders and electrochemical behavior and rheology of FEs were investigated to reveal the relationship between FE properties and desalination performance. Results show that, due to their unique electrosorption behavior, excellent conductivity, and enhanced conductivity through a bridging effect, CNT-based FE (carbon loading: 3 wt %) achieved the fastest (8.3 mg s–1 m–2) and the most stable desalination (charge efficiency: 93.3%). A faster desalination (13.2 mg s–1 m–2), due to significantly improved electroconductivity (13.2 times) with only a slight viscosity increase (1.1 times), was achieved by adding CNTs into 6.91 wt % AC-based FE for a 7.41 wt % total carbon concentration. This study highlights the importance of the intrinsic properties of carbon materials, especially electroconductivity, in promoting FCDI desalination performance.