Study on the synthesis and thermal properties of magnesium chloride hexahydrate–magnesium sulfate heptahydrate–activated carbon phase change heat storage materials

As the phase change heat storage materials, the hydrated salts have good application prospects. However, the supercooling and phase separation of hydrated salts are two key factors, which affect their thermal properties and thermal stability. Moreover, the thermochemical reaction of hydrated salts below 130 °C is very important for its phase-change heat storage performance. A new composite phase-change material (CPCM) with good heat storage performance and thermal stability composed of magnesium chloride hexahydrate (MCH), magnesium sulfate heptahydrate (MSH), and activated carbon (AC) was synthesized. The effects of AC on supercooling, phase separation, and phase transition temperature of CPCM were investigated. The results showed that phase separation and supercooling were completely eliminated in CPCM with 3.0 wt% AC, and the content of AC had a significant effect on thermal cycle stability, heat storage performance, and enthalpy balance. CPCM has good thermal cycle stability. CPCM with the content of 3.0 wt % AC possessed the phase transition temperature of 90.21°C and the phase transition enthalpy of 156.14 kJ kg−1, which is very suitable for household heat storage.