Improving the Thermal and Photothermal Performances of MXene-Doped Microencapsulated Molten Salts for Medium-Temperature Solar Thermal Energy Storage

Molten salts are widely used as thermal energy storage materials for solar thermal applications, but they suffer from low photothermal conversion efficiency and potential leakage and corrosion issues. In this paper, MXene doping was proposed to improve the thermal properties and photothermal conversion efficiency of microencapsulated molten salts. MXene nanomaterials, which have excellent thermal conductivity and photothermal conversion efficiency, were used to dope the molten salts. The results tested by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) indicate that MXene was well doped in the molten salt microcapsules. Fourier transformation infrared (FT-IR) spectroscopy was used to confirm that the microencapsulation of the molten salt by silica is a physical action. The results of X-ray diffractometry (XRD) show that the crystal structure of the molten salt maintained stability. The results obtained from the Hot Disk thermal constant analyzer and photothermal conversion experiments showed that thermal conductivity and photothermal conversion efficiency of the MXene-doped microcapsules were increased by 156.2% and 169.4%, respectively. The differential scanning calorimeter (DSC) results indicated that the MXene-doped microcapsules had a reduction of 49.6% in the supercooling degree. The thermal reliability of the MXene-doped microcapsules was 94.0% after 50 thermal cycles. This approach provides a promising solution for improving the thermal properties and photothermal conversion efficiency of microencapsulated molten salts for medium-temperature solar thermal energy storage.