Thermodynamic and Electrochemical Properties of Quaternary Ammonium-Salt-Based Deep Eutectic Solvents

As novel solvents possessing numerous unique properties and promising application prospects, deep eutectic solvents (DESs) hold significant importance in the field of green chemistry and sustainable development. In this study, tetraethylammonium bromide (TEAB) was selected as the hydrogen bond acceptor (HBA), and ethylene glycol (EG), levulinic acid (LA), and lactic acid (EA) were selected as the hydrogen bond donors (HBD) for the synthesis of a series of DESs. The volumetric properties, surface tension properties, electrical conductivity properties, and electrochemical windows of these DESs were systematically investigated. Thermodynamic parameters such as the thermal expansion coefficient, molecular volume, molar volume, molar surface Gibbs energy, and molar electrical conductivity were calculated based on experimental data for the density, surface tension, and electrical conductivity. The electrochemical potential windows (EPW) of all DESs were arranged in the following order: [TEAB:4EG] and [TEAB:6EG] (EPW = 3 V) > [TEAB:6LA] (EPW = 2.8 V) > [TEAB:4LA] (EPW = 2.3 V) > [TEAB:6EA] (EPW = 2.2 V) > [TEAB:4LA] (EPW = 2 V). Therefore, this study provides important theoretical support for the design and potential application of quaternary ammonium-salt-based DESs by further studying the thermodynamic properties of DESs.