Synthesis and Properties\nof Physically Cross-Linked\nSilica-Mediated Novel Eutectogels Developed from Carboxylic Acid-Based\nNatural Deep Eutectic Solvents

Solid composite electrolytes are acclaimed for their\nability to\novercome limitations associated with liquid electrolytes, while still\nretaining crucial characteristics of the latter. Particularly within\nthe realm of energy storage, these electrolytes have garnered substantial\ninterest over the past decade. This study presents an investigation\ninto four eutectogels developed by encapsulating four binary deep\neutectic solvents (DESs) into a matrix of silica (SiO<sub>2</sub>)\nthrough a nonaqueous sol–gel technique. Each DES consists of\na naturally occurring carboxylic acid and dl-menthol, mixed\nin a carefully optimized molar ratio. The properties of these eutectogels\nare thoroughly characterized by employing analytical techniques including\nfield emission scanning electron microscopy (FESEM), field emission\ntransmission electron microscopy (FETEM), Fourier transform infrared\n(FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis\n(TGA), differential scanning calorimetry (DSC), and cyclic voltammetry\n(CV). The DESs, rendered amorphous and porous post gelation, maintain\ntheir structural integrity following their incorporation into the\nSiO<sub>2</sub> matrix. Thermal analyses of the gels reveal only gradual\nmass loss up to ∼120 °C, indicating their decent thermal\nstability. The eutectogels are double-layer capacitive within an exceptionally\nwide operational potential window (OPW) of 4 V, accentuating their\npracticality in electrochemical applications.