Development of a low-cost deep eutectic solvent based on zinc nitrate hexahydrate salt/ethylene glycol as an electrolyte for rechargeable zinc air batteries

Abstract In this study, a cheap zinc nitrate hexahydrated (ZNH)/ethylene glycol (EG) deep eutectic solvent (DES) was developed as a substitute electrolyte for rechargeable zinc air batteries using the heating method. The synthesized ZNH/EG based DESs were characterized by ionic conductivity (σ), refractive index, density, viscosity, thermogravimetric (TGA), Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry (CV) measurements. The results revealed that at a 1:6 of DES lowest viscosity values of 579,381,119,110, and 58 centipoise (cp) were obtained at 20, 30, 60, 100, and 200 corresponding spindle speeds rotation per minute respectively. Similarly, lower density value of 1.392 g/cm3, lower refractive index value of 1.441 and higher conductivity (σ) of 7.51 ms/cm were obtained at 1:6 of DES. The cyclic voltammetry (CV) result also presented a wider range of electrochemical potential window (EPW) value of 1.06 V. This could be due to the delocalization of charged ions with a larger void volume that builds within the solution, showing the reversibility of electrochemical electrolyte. Hence, the result showed the DES with a 1:6 molar ratio could be a promising electrolyte for rechargeable zinc air batteries.