Carbon electrode with cross-linked and charged chitosan binder for enhanced capacitive deionization performance

Capacitive deionization (CDI) has emerged an energy-efficient and operation-simple electrochemical desalination processes among water treatments. Polymeric binder as an important component of CDI electrode is desired to have good adhesion, wettability and stability. In order to reduce the chemical uses and further enhance the CDI performance, we have designed the preparation of the crosslinked chitosan (CS) with glutaraldehyde (GA), and coated it on the activated carbon (AC) electrodes for desalination. By adjusting different GA contents, the CS crosslinked with GA (CS + 3GA) binder with stable three-dimensional (3D) networks were fabricated due to the utilization of tertiary amines (C=N), which exhibited strong adhesive property. Moreover, the CS + 3GA not only possessed good hydrophilicity, but also carried more positive charges that function as ion anion exchange membrane. In the electrosorption tests, an asymmetric CDI system (CS + 3GA//PVDF) was assembled via pairing a composite carbon anode coated with CS + 3GA binder, and a PVDF-bound carbon cathode. The studies demonstrated that CS + 3GA//PVDF cell showed excellent salt adsorption capacity (SAC) of 16.0 mg g−1 over 2 times higher than PVDF//PVDF, and good charge efficiency (CE) of 62.5% at 1.2 V. More importantly, CS + 3GA//PVDF displayed a remarkable regeneration performance that retention rate of 82.8% and approached that of PVDF//PVDF-M (83.2%) over 80 regeneration cycles. In addition, CS + 3GA//PVDF cell could be implemented at 1.4 V for desalination, which showed the unprecedented SAC of 18.4 mg g−1. The cross-linked and charged CS + 3GA binder coated with the carbon anode possesses the merits of being inexpensive, green and stable, making it a promising candidate for future CDI applications.