Study on a deep eutectic solvent of magnesium chloride hexahydrate and urea as a high-performance electrolyte for supercapacitors

Deep eutectic solvents (DESs) based on metal salts are promising candidates for high-performance supercapacitor electrolytes due to their high conductivity and excellent stability. This study utilized a DES consisting of MgCl2 center dot 6H2O and urea as a novel electrolyte for supercapacitors. The influence of varying molar ratios on the electrolyte's physical properties, microscopic structure, and electrochemical performance was thoroughly investigated. The results indicated that as the urea content in the electrolyte increased, the carbonyl oxygen in urea replaced part of the chloride ions and the oxygen atoms in water molecules, becoming the primary coordinating atom for Mg2+. This substitution resulted in a more stable coordination structure, enhancing the electrolyte's thermal stability, conductivity, and electrochemical performance. At room temperature, the electrolyte with a molar ratio of MgCl2 center dot 6H2O to urea of 1:6 exhibited a conductivity of 4.90 mS center dot cm- 1, an electrochemical stability window of 2.35 V, a specific capacitance of 81.75 F center dot g- 1, and an energy density of 9.05 Wh center dot kg- 1. This study offers valuable insights into the development of cost-effective, environmentally friendly, and high-performance supercapacitor electrolytes.