Efficient synthesis of regular spherical GO/SiO2@Solar Salt microcapsules to enhance heat-storage capacity and cycle stability

The sol–gel method was used to overcome the disadvantages associated with the high water solubility of molten salt into advantages, and a W/O emulsion system was constructed. The interfacial polymerization reaction was initiated by ammonium hydroxide to generate a SiO2 shell layer, which served as a microcontainer for Solar Salt to prepare more stable regular spherical microcapsules with a diameter of 886 nm. Meanwhile, the oxygen-containing functional groups on the surface of graphene oxide (GO) were combined with the shell of the SiO2@Solar Salt phase-change heat-storage microcapsule through shared electron pairs and hydrogen bonds, such that they were uniformly distributed on the GO layer. The synthesized composite material exhibited a typical morphology of microcapsules with a core–shell structure uniformly loaded on the sheet. This study proves that the encapsulation of SiO2 and introduction of the high thermal conductivity enhancement phase increased the thermal conductivity of the microcapsules by approximately 45% compared with pure nitrate and maintained a high specific heat capacity of 1.44 J/(g·K). In addition, the microcapsules exhibited excellent photothermal conversion efficiency, effectively absorbing visible light and increasing the heat storage rate. The addition of GO nanosheets and SiO2 increased the structural stability of the composite material and its cycle life. Owing to the exquisite composite structure, the structural composition of the microcapsule remained unchanged after 500 thermal cycles, maintaining 98.5% latent heat, 99% heat capacity, and good thermal conductivity. This study provides a new solution for the efficient microencapsulation of molten salt heat storage materials.