The application of magnesium nitrate hexahydrate/hybrid carbon material phase change composites in solar thermal storage

Abstract Background In this study, a series of phase change composites were developed. Phase change materials (PCMs) are substances with a high heat of fusion, thereby possessing great potential for solar thermal storage. However, their disadvantages, such as low thermal conductivity, phase separation, and supercooling, limit their further applications. Objective In this study, magnesium nitrate hexahydrate (MNH) was used as the phase change material, and different proportions of photothermal materials were added to improve the thermally conductive property and solar thermal storage efficiency of MNH. Methods This study used magnesium nitrate hexahydrate (MNH) as the substrate. In addition, different proportions of photothermal materials (carbon nanotubes, nano‐graphite, graphene, and partially reduced graphene oxide) were added to promote the efficiency of thermal energy storage. Additionally, a fixed ratio of carboxy methyl cellulose (CMC) was added. The phase change temperature and enthalpy change of the phase change material samples were explored and analyzed by differential scanning calorimeter (DSC). In addition, the thermophysical properties, photothermal storage performance, and thermal reliability analysis of the samples were investigated. Results The results showed that the PCM composites prepared with nano‐graphite have higher latent heat and longer time of phase change. However, the composites prepared with carbon nanotubes (CNTs) have lower latent heat and a shorter time of phase change. Therefore, the partially reduced graphite oxide (PRGO)‐containing composites can retain the latent heat storage capacity of nano‐graphite and decrease the time of phase change, thereby improving the photothermal storage efficiency. The results reveal that the solar thermal storage efficiency of the composite with both CNTs and PRGO could reach up to 0.716. Conclusions MCGOT‐1 and MCGOT‐2 have high latent heat values, and the phase transition time is short. Therefore, the thermal energy storage efficiency can be as high as 0.716. In addition, compared with related literature, the photothermal storage efficiency of MCGOT‐2 increased by about 2 times. Therefore, the environmentally friendly composites developed in this study have a high potential to be used in solar energy storage and energy‐saving systems.