Novel eutectogels derived from an ionic-liquid-based deep eutectic solvent as electrolytes for supercapacitors: synthesis and characterization

Abstract

Solid or quasi-solid electrolytes are acclaimed for their ability to overcome limitations associated with liquid electrolytes, while still retaining crucial characteristics of the latter. Particularly within the realm of energy storage, these electrolytes have garnered substantial interest over the past decade. This study presents an investigation into two hybrid eutectogels obtained from the encapsulation of an ionic-liquid-(IL-) based binary deep eutectic solvent (DES) within a solid matrix of titania (TiO₂) or silica (SiO₂) through a non-aqueous sol–gel route. The DES is prepared by mixing the IL 1-butyl-3-methylimidazolium methanesulfonate ([BMIM][MeSO₃]) and N-methylacetamide (NMAc) in a carefully optimized molar ratio of 1 : 2. The properties of the eutectogels are thoroughly examined employing analytical techniques including field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, field emission transmission electron microscopy (FETEM), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Remarkably, the structural integrity of the DES remains unaltered following its incorporation into the matrices. The eutectogels exhibit a double-layer capacitive behavior within a wide operating potential window (OPW) of 3 V. Specific capacitance and ionic conductivity as high as 16.32 F g⁻¹ and 1.27 mS cm⁻¹ are obtained at room temperature with specific energy and specific power of 20.39 W h kg⁻¹ and 3.31 kW kg⁻¹ respectively, thus underscoring their potential utility in applications concerning electrochemical supercapacitors.