Investigating the Electrochemical Properties of Ionic-Liquid-Mediated Inorganic Eutectogels Derived from Carboxylic-Acid-Based Hydrophobic Natural Deep Eutectic Solvents

Abstract

The growing demand for sustainable energy storage technologies drives the development of environment-friendly electrolytes with superior electrochemical performance. Conventional liquid electrolytes face challenges such as leakage and limited portability. Solid or quasi-solid electrolytes like ionogels and eutectogels offer promising alternatives; however, ionogels can be costly due to extensive use of ionic liquids (ILs), and eutectogels often suffer from restricted operating potential window. While eutectogels developed from natural deep eutectic solvents (NADESs) offer more benignity and a wider potential window, they possess low ionic conductivity. This study introduces hybrid eutectogel electrolytes by confining hydrophobic NADESs within a titania (TiO₂) matrix via a non-aqueous sol–gel process, mediated with 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). The goal is to address conductivity limitations observed in earlier NADES-based eutectogels by harnessing the synergistic properties of NADES, IL, and TiO₂. Electrochemical analyses using cyclic voltammetry and electrochemical impedance spectroscopy with reduced graphene oxide electrodes reveals a wide 4 V potential window, high ionic conductivity (14.53–16.28 mS·cm⁻¹), and decent specific capacitance (16.23–47.72 F·g⁻¹). Achieving specific energy up to 106 W·h·kg⁻¹, these eutectogels show strong potential as electrolytes for high-performance supercapacitors, paving the way for further material optimization.

Graphical Abstract