The role of nano-hydroxyapatite bearing zwitterion within carboxylated chitosan hydrogel electrolyte in improving supercapacitor performance

In this study, we intend studying the role of nano-hydroxyapatite bearing zwitterion within carboxylated chi-tosan hydrogel electrolyte in improving supercapacitor performance. First, we carry out the ring-opening addition of (3-Aminopropyl) triethoxysilane with 1,4-Butane sultone to obtain zwitterionic silane (ZSi). Then, ZSi is grafted onto nano-hydroxyapatite (nHA) by condensation process to obtain nano-hydroxyapatite grafted zwitterionic silane (nHA-ZSi). The successful synthesis of nHA-ZSi is confirmed by Fourier transform infrared spectroscopy and 13C Nuclear magnetic resonance. Differential scanning calorimetry shows that the incorporation of nHA-ZSi reduces the crystallization of the polymer matrix due to filler effect. Afterwards, nHA-ZSi with 5%, 10%, 20%, 30% are mixed with carboxylated chitosan (CCS) to obtain composite films (CCS/nHA-ZSi). The stress-strain curves of CCS/nHA-ZSi are characterized by tensile testing. Ionic conductivities of hydrogel electrolytes are estimated by soaking CCS/nHA-ZSi in 1 M Na2SO4 via electrochemical impedance. Furthermore, CCS/nHA-ZSi hydrogel electrolytes are assembled with symmetric carbon electrode for electrochemical tests, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance. The specific capacitance increases with the addition of nHA-ZSi; reaches the maximum at 20%; and then decreases due to aggregation. After 5000 cycles, CCS/20% nHA-ZSi supercapacitor has 98% capacitance retention at 6 mA/cm2. This study demonstrates that nano-hydroxyapatite bearing zwitterion is a beneficial additive for both mechanical strength and ionic conductivity in hydrogel electrolytes.

Automated summary

This study investigates the role of nano-hydroxyapatite bearing zwitterion in carboxylated chitosan hydrogel electrolyte for improved supercapacitor performance. The successful synthesis of the composite is confirmed by various characterization techniques. The results show that the addition of nano-hydroxyapatite bearing zwitterion significantly enhances the performance of supercapacitors.