Triple capacitance via the dehydration of saturated water from carboxylated chitosan bearing zwitterion electrolytes

Background: In the solid-state polymer electrolyte, the saturated water plays an role in increasing ionic conductivity but decreasing the electrochemical window. The water retention effect on zwitterionic polymer electrolyte is investigated in this study. Methods: Carboxylated chitosan (CCS) was subjected to oxa-Michael addition with sulfobetaine methacrylate (SBMA) to produce CCS-SBMA. Its structure was investigated by IR and ¹H NMR and used the raman spectrum to observe three different types of water. CCS-SBMA electrolyte and carbon electrode were assembled into supercapacitor for electrochemical testing. Significant findings: CCS-SBMA was grafted 45.7% of sulfobetaine group via Nuclear Magnetic Resonance (NMR) spectra. During dehydration of saturated water from CCS-SBMA polymer electrolyte to 90% retention, the free water proportion decreased, and the bound water proportion increased via Raman spectra analysis. Accordingly, the electrochemical window increased from 1.6V to 2.05V with 10% dehydration of saturated water. Surprisingly, the supercapacitor performance with 90% water retention showed triple specific capacitance of 414.3F/g in comparison with 138.6F/g evaluated from galvanostatic charge-discharge analysis. In this study, CCS-SBMA bearing zwitterion was designed as polymer electrolyte to remain bound water proportion and enhance ion-dissociation during dehydration of saturated water for superior capacitance performance of solid-state supercapacitor.