Development and Characterization of Highly Ionic Conductive Hydrogel Electrolytes for Supercapacitors

In this study, epoxidized natural rubber (ENR-25) in combination with acrylamide and acrylic acid hydrogels with N,N′-methylenebis(acrylamide) as a chemical cross-linking agent was formulated using a free-radical polymerization technique. Different vol % of sodium hydroxide (NaOH) (5, 10, 15, and 20 vol %) was used to prepare the hydrogel electrolyte and labeled as NR/NaOH5, NR/NaOH10, NR/NaOH15, and NR/NaOH20, respectively. The synthesized hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD). The ionic conductivity was measured using electrochemical impedance spectroscopy (EIS), and it was found that the NR/NaOH20 hydrogel obtained the highest ionic conductivity of 8.72 mS cm–1 with the lowest activation energy of 0.1045 eV. Symmetric supercapacitors were fabricated using NR/NaOH5, NR/NaOH10, NR/NaOH15, and NR/NaOH20 as hydrogel electrolytes and electrochemical studies such as cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) analysis were conducted. The electrochemical performance disclosed that the hydrogel containing the highest amount of NaOH (NR/NaOH20) showed maximum specific capacitances of 49.66 F/g at 5 mV/s and 43.24 F/g at 300 mA/g.