Effect of ethylene glycol on deep eutectic solvent properties: dual functionality of zinc chloride as hydrogen bond acceptor and salt

This study presents the development and analysis of novel deep eutectic solvents (DESs) composed of glycerol, zinc chloride, and ethylene glycol for application in supercapacitors. Various molar ratios were explored to optimize the physical and electrochemical properties of the DESs. The formulation with moderate ethylene glycol content demonstrated improved viscosity and ionic conductivity, which facilitated enhanced ionic mobility. Electrochemical characterisation confirmed superior specific capacitance and ionic conductivity for the optimized sample. This work underscores the critical role of composition tuning in DES systems to achieve an optimal balance between viscosity and conductivity, ultimately advancing the performance of supercapacitor devices. A thermally stable ZnCl₂–glycerol–ethylene glycol DES was developed, exhibiting high electrochemical stability, optimized viscosity, and real-world functionality, including LED illumination—highlighting its potential in energy storage applications. • ZnCl 2 as the HBA, glycerol as the HBD, and ethylene glycol as a co-solvent additive used to prepare DES. • ZnCl 2 , Glycerol and ethylene glycol added in molar ratios of 1:10:2 for DES-2. • DES-2 has the lowest viscosity (543.2 mPa·s), enhancing ion mobility, the highest capacitance (64.80 F/g) with optimal conductivity, the widest stability window (2.87 V) among tested DESs and the highest ionic conductivity (0.27 mS cm −1 ), boosting performance. • All DES samples powered a 6 V LED, proving practical use.