Study on the functionalization of activated carbon and the effect of binder toward capacitive deionization application

Abstract

Abstract Capacitive deionization (CDI) is a high-performance and low-cost technology for desalination. Normally, the CDI electrodes are fabricated using a slurry of activated carbon (AC) with a polymeric binder. In this study, AC from coconut shell charcoal was modified in 7% HNO3 solution, which is emphasized by the formation of functional groups on its surface after modification. The isoelectric point (pHIEP) of modified AC is found at 3.02, which confirmed the formation of carboxyl and phenolic hydroxyl groups on the surface. The effect of polyvinyl alcohol (PVA) and polyvinylidene fluoride (PVDF) polymeric binders on characteristics as well as the specific capacitance of the CDI electrodes are investigated. The hydrophilic binder of PVA-based with mesh structure has proven to be promising for salt adsorption ability with the specific capacitance of 47.78 F·g−1, which is higher than that of PVDF binder (17.96 F‧g−1). The composite electrode based on mAC, Gt, and PVA-GA binder has a salt adsorption capacity of 8.9 mg·g−1 and good cyclic stability (retained 94%) after 50 adsorption–desorption cycles at an applied voltage of 1.2 V.