Preparation a three-dimensional hierarchical graphene/stearic acid as a phase change materials for thermal energy storage

Three-dimensional hierarchical graphene (3DHG) was compounded with stearic acid (SA) to obtain SA/3DHG composite phase change materials (PCMs). The specific surface area and pore volume of 3DHG are 393 m(2)g(-1)and 0.57 m(3)g(-1). The phase-transition temperatures of SA/3DHG composites keep at 69 1 degrees C with different adding amounts of 3DHG, meanwhile SA/3DHG-3 possesses the melting enthalpy of 189.7 Jg(-1)and solidifying enthalpy of 188.8 Jg(-1). 3DHG shows significant enhancement on the thermal properties and shape stability of SA. The thermal conductivity of SA/3DHG-3 reaches to 0.93 Wm(-1)K(-1), which is as high as 2.8 times of pure SA (0.33 Wm(-1)K(-1)). The investigations of XRD and FTIR indicate that no chemical but physical combination occurs between SA and graphene. 3DHG has substantial meso-porous/macro-porous structure for packaging SA to form the irregular core-shell structure. The hierarchical pores are also beneficial to the graded thermal transfer inside SA/3DHG composite PCMs. The efficiency of heating process from 25 degrees C to 90 degrees C was improved by about 57%. Furthermore, the 3D network skeleton built up by graphene sheets can form an effective and connected heat transfer paths for SA, thus improves the endothermic and exothermic efficiency of SA/3DHG composite PCMs. This work emphasizes the 3D hierarchical structure of graphene and provides a promising way to prepare composite PCMs with high large storage density and heat transfer efficiency.