Synthesis and characterization of self-healable poly (acrylamide) hydrogel electrolytes and their application in fabrication of aqueous supercapacitors

Abstract

With overwhelming progress in the field of electronic technology, self-healable hydrogel electrolyte-based supercapacitors are of significant interest as a power source in wearable energy storage devices. Self-healable hydrogel with unique three-dimensional porous microstructure, unprecedented self-healing, high capacitive energy density, low power density has been synthesized by in situ polymerization of acrylamide in the presence of exfoliated sodium montmorillonite (Na-MMT) clay as non-covalent cross-linker. Furthermore, addition of lithium trifluoromethanesulfonate (LiTF) salt converted the hydrogel into electrolyte for use in supercapacitor. Hydrogel electrolytes were prepared containing 10, 20, 30, and 40 wt% salt (AAM1, AAM2, AAM3, and AAM4), respectively. Acrylamide, clay and salt interactions were explored by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and energy dispersive x-ray analysis (EDX). X-ray diffraction (XRD) analysis reveals amorphous nature whereas FTIR and transference number measurements prove the complexation and presence of ionic species in the hydrogel electrolytes. Ionic conductivity and transport studies for hydrogel electrolyte containing 30 wt% of LiTF showed maximum ionic conductivity of 9.34 × 10−3 S/cm and number density of 70.7 × 10 20 cm−3, diffusion coefficient of 2.16 × 10 −9 cm2/s, ionic mobility of 0.854 × 10−7 cm2/V.s among all the synthesized hydrogel electrolytes. The electrochemical performance of the fabricated device disclosed the maximum significant specific capacitance of 102 F/g at 3 mV/s and 157 F/g at 50 mA/g along with power density of 50 W/kg and energy density of 21.59 W h/Kg, respectively for hydrogel electrolyte (AAM3) containing 30 wt% of the LiTF. Self-healing properties of hydrogel electrolyte have been confirmed by its use in supercapacitor where it retained its self-healing properties. The self-healable supercapacitor was used to light up 2 V light emitting diode (LED). Hence, investigations suggest the potential application of the hydrogel electrolytes with 30 wt% LiTF in the supercapacitors.