Construction and investigation of paraffin based phase change composite containing chitosan@expanded graphite aerogel as structure skeleton for low temperature thermal energy storage

This work concerns the construction of a paraffin based shape-stable phase change composite with the use of chitosan@expanded graphite aerogel as structure skeleton for low temperature thermal energy storage application. A so-called freeze-drying integrated with infiltration approach is used for the material fabrication and a battery of experiments are performed to evaluate the composite microstructure features, chemical compatibility, and thermophyscial properties as well as cycling performance. The results show that the chitosan@expanded graphite aerogel forms a three-dimensional interconnected structure in the composite, which could effectively accommodate paraffin and prevent liquid phase leakage over heating process. More than 92 wt% of paraffin could be encapsulated in the composite, and at such a composition, the composite presents a melting temperature of 36.3 °C and a latent heat of 183.3 kJ/kg. Owning to the high heat conductivity of expanded graphite, the composite effective thermal conductivity could be significantly enhanced. For a given expanded graphite mass ratio of 33.3 % in the aerogel, the composite thermal conductivity could be reached to 1.21 W/m·°C, which is increased by 5.26 times in comparison with the pure paraffin. The composite also exhibits excellent shape stability and cycling performance. After experienced 300 times of repeated heating-cooling cycles, only less than 3 % reduction in latent heat is observed, demonstrating the composite has achieved splendid cycling ability and could be a competitive candidate utilized in low temperature thermal energy storage fields.