Synthesis and Properties of Physically Cross-Linked Silica-Mediated Novel Eutectogels Developed from Carboxylic Acid-Based Natural Deep Eutectic Solvents

Solid composite 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 four eutectogels developed by encapsulating four binary deep eutectic solvents (DESs) into a matrix of silica (SiO2) through a nonaqueous sol–gel technique. Each DES consists of a naturally occurring carboxylic acid and dl-menthol, mixed in a carefully optimized molar ratio. The properties of these eutectogels are thoroughly characterized by employing analytical techniques including field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and cyclic voltammetry (CV). The DESs, rendered amorphous and porous post gelation, maintain their structural integrity following their incorporation into the SiO2 matrix. Thermal analyses of the gels reveal only gradual mass loss up to ∼120 °C, indicating their decent thermal stability. The eutectogels are double-layer capacitive within an exceptionally wide operational potential window (OPW) of 4 V, accentuating their practicality in electrochemical applications.