Construction and evaluation of a novel three-electrode capacitive deionization system with high desalination performance

Abstract

• A novel 3-CDI system with high desalination performance is designed. • Higher SAC and faster SAR are achieved in 3-CDI compared to FB CDI. • Higher Λ, lower energy consumption, shorter desorption time and good cyclic stability are realized in 3-CDI. • More FTE electrode mass is used for desalting compared to the reported value. • Analysis of pH fluctuations is used to explain the different adsorption processes in FB CDI and 3-CDI. Exploiting a high-performance capacitive deionization (CDI) system with both high salt adsorption capacity (SAC) and fast salt adsorption rate (SAR) is a challenge for desalination. Herein, a novel three-electrode CDI (3-CDI) with both flow-through (FTE) electrode and flow-by (FB) electrode is originally developed. Experimental results indicate that a higher SAC and faster SAR are realized in 3-CDI compared with FB CDI via using conventional symmetrical/ asymmetrical electrodes. Besides, 3-CDI achieves a higher charge efficiency (Λ), lower energy consumption, shorter desorption time and good cyclic stability. Further analysis shows more FTE electrode mass in 3-CDI can be used for desalting compared with the reported value. However, as the number of FTE electrodes increases, the electrode mass utilization rate will decrease in turn. Moreover, it is found that the deionization process of both CDI cells is different. pH fluctuations analysis reveals that 3-CDI can prolong the time required for the electrode to reach the desalination equilibrium and overtly delay the time for the conversion of desalination behavior to faradaic reactions. Overall, this work sheds light on the effective utilizing electrode mass for desalination and has a reference for designing high-performance CDI cells from the perspective of hybrid cell structure.