Shape-stabilized phase change material (SSPCM) is a promising thermal energy storage material in energy-saving buildings. However, its flammability leads to a fire risk. The conventional bulk addition method has a limited flame-retardant effect. Herein, a series of surface coatings with various flame retardants were introduced to improve flame retardance of SSPCM. The results showed that all of the coatings had flame-retardant effects on SSPCM; In particular, the EG coating performed the best: the horizontal burning time was the longest, the limiting oxygen index was above 30%, the V0 classification was obtained, the peak heat release rate was sharply decreased from 1137.0 to 392.5 kW/m² and the burning process was prolonged with the least total smoke production. The flame-retardant mechanism was discussed. As paraffin easily evaporated from the SSPCM at a moderate temperature, it caused flames. After being surface coated, the EG-based coatings first hindered the volatilization of paraffin at a moderate temperature, then expanded and formed thick porous carbon layers at a high temperature to block the transfer of combustibles, oxygen and heat between the bulk and the environment. Therefore, the surface coating strategy achieved a desirable flame-retardant level with fewer flame retardants.

The storage and utilization of waste heat in low and medium temperature ranges using phase change materials (PCMs) is an effective technology to improve energy utilization efficiency in combined cooling, heating, and power (CCHP) systems. In this paper, stearic acid/inorganic porous matrix phase change composites were developed to store waste heat for hot water systems. Among them, stearic acid/expanded graphite (EG) phase change composite was highlighted and the thermal physical properties, the dynamic response, and the long-term cyclic stability were evaluated. The stearic acid concentrations in the composites were over 95 wt%. The thermal diffusion coefficients were 3–5 times higher than pure stearic acid, independent of composite densities. Accordingly, the heat storage and release times were decreased by up to 41% and 55%, respectively. After 100 cycles, the composites maintained good dynamic response and long-term cyclic stability, with heat storage density of 122–152 MJ/m³. Hence, this stearic acid/EG phase change composite exhibits excellent comprehensive performances. It is also easy to be prepared and flexible for various types of heat exchangers.