Analyzing the Solvation and Electrochemical Behavior of Triethylmethylammonium Tetrafluoroborate in Pure and Aqueous Ethaline Deep Eutectic Solvent: Experimental and Computational Approaches

Abstract

The growing population has led to an increase in global energy demands. Efficient energy storage methods and devices are the need of the hour. Deep eutectic solvents (DESs) being only two decades old have presented themselves as suitable candidates for electrolytes in energy storage devices. These solvents are cost-effective and environmentally friendly and can be designed in numerous ways to meet the targeted applications. In order to make these solvents more environmentally friendly and cheap, water as an additive can be explored. In this regard, electrochemical and thermophysical properties like apparent and partial molal volumes, isentropic compressibility, and apparent and partial molal isentropic compressibility of solutions comprising triethylmethylammonium tetrafluoroborate (TEMABF₄) in pure and aqueous DES (ethaline) were determined using experimental and computational techniques. The tetra-alkyl salt was found to act as a structure breaker after the analysis of thermophysical parameters in all of the solvent systems under consideration. Upon moving from pure to aqueous DES systems, substantial rise in the ionic conductivity and drop in the viscosity values were observed while maintaining an electrochemical window of 2.3 and 1.7 V for pure DES and aq. DES, respectively. Computational studies (RDG, MEP, and NCI) and FTIR findings complemented the experimental results and showed increased kinetic stability upon addition of water, confirming significant H-bonding between water and DES and increased solvation of ionic components in water.