Synthesis and characterization of N hydroxymethylacrylamide based self-healable hydrogels for supercapacitor / Silvaraj David

Silvaraj , David (2022) Synthesis and characterization of N hydroxymethylacrylamide based self-healable hydrogels for supercapacitor / Silvaraj David. Masters thesis, Universiti Malaya.

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Abstract

Hydrogels are garnering increasing interest in scientific and technological development as a result of their ability to be able to hold a large volume of water. This characteristic is possible due to the presence of a hydrophilic polymer strain, which results in the material's widespread use. Due to their soft physical properties, they are an attractive material for use as electrolytes in supercapacitors. However, when hydrogels are used as the electrolyte in supercapacitors, critical issues such as electrochemical performance, stability, and a small potential window are raised in comparison to supercapacitors constructed using organic electrolytes. Recent advancements in the development of a unique water-in-salt hydrogel electrolyte supercapacitor with a broad potential window has sparked attention. As a result, the present work utilised the free radical method to synthesize poly (N-hydroxymethylacrylamide) (PNHMA) hydrogel and lithium salt-containing hydrogel electrolytes. The free radical initiator was ammonium persulfate, while the crosslinking agent was sodium montmorillonite (clay). Lithium trifluoromethanesulfonate (LiTF) salt was introduced as an ion source due to the salt's ionization producing free-moving ions. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and field emission scanning electron microscopy (FESEM) were used to analyse the produced hydrogel electrolytes. The ionic conductivity of the produced hydrogel electrolytes was determined using electrochemical impedance spectroscopy (EIS). The hydrogel electrolyte containing 30 wt.% LiTF (NHMA3) demonstrated the maximum ionic conductivity of 6.6 x 10-3 S/cm and the lowest activation energy (Ea) of 0.085 eV. The hydrogel electrolytes were embedded in an electric double layer capacitor (EDLC) using an activated carbon electrode and then characterized using cyclic voltammetry (CV) and galvanostatic charge discharge (GCD). These two approaches demonstrated that the hydrogel based supercapacitor with the setup of AC/NHMA3/AC exhibited a maximum specific capacitance of 165.19 F/g at 5 mV/s and 287.96 F/g at 200 mA/g, as well as a specific energy of 39.63 W h/kg and a specific power of 199.16 W/kg. Additionally, after 5000 cycles at a current density of 5 A/g, the supercapacitor retained 98.5 percent capacitance. As a result, it can be concluded that hydrogel electrolytes created in this study have tremendous potential for smart, lightweight, and flexible electronic devices.

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