In response to the performance limitations of traditional heat transfer fluids under extreme conditions, a series of organic/inorganic deep eutectic solvents (DES), composed of ethylene glycol and different types of acetates, have been developed, and their downstream thermophysical properties, as well as their potential applications in nanofluids, have been explored. It is found that the prepared DESs significantly broaden the liquid phase temperature range, which ranges from −14~196 °C to −40~201 °C. The initial decomposition temperature increases from 85 °C to 130 °C, and the peak decomposition rate shifts from 175 °C to 206 °C. Subsequently, nanofluids were prepared by employing the selected ethylene glycol: potassium acetate-5:1 DES with carbon nanotube as nanofiller. The results reveal that the thermal conductivity of the nanofluid could be increased by approximately 3% compared to the base fluid, and the specific heat capacity was enhanced by 7.5% with a photothermal conversion efficiency reaching up to 42.7%. These results highlight the promising thermal stability and heat transfer properties of ethylene glycol-acetate DESs. Moreover, the nanofluids prepared from those DESs as base fluids provide useful references for the development of novel, green, and high-efficiency energy transportation fluids.
