Enhanced desalination via cell voltage extension of membrane capacitive deionization using an aqueous/organic bi-electrolyte

Abstract

Capacitive deionization (CDI) is a promising desalination technology based on ion electrosorption. The desalination capacity of CDI using carbon electrodes has remained limited due to a low operating cell voltage of around 1.2 V originating from the electrochemical stability window of water. Here, we report a novel multi-channel membrane CDI system that allows extension of the cell voltage by immersing one carbon electrode in an organic electrolyte and the other in an aqueous electrolyte. The resulting membrane CDI system using an aqueous/organic bi-electrolyte consists of two side-channels for supporting electrolytes with activated carbon electrodes and middle-channel for the feedwater flow. The middle-channel is separated by ion exchange membranes from the side-channels allowing highly concentrated water and organic supporting electrolytes (1 M NaCl in water and 1 M NaClO4 in propylene carbonate), respectively. Using an organic electrolyte for negative electrode (Na+ adsorption), the stable operating cell voltage was increased to 2.4 V. At the operating cell voltage of 2.4 V, the system provided an excellent desalination capacity of 63.5 ± 4 mg/g with charge efficiency of 95%.