Graphene-decorated silica stabilized stearic acid as a thermal energy storage material

Abstract

Novel thermal energy storage materials were synthesized from graphene-decorated silica (SG) and stearic acid (SA) by vacuum impregnation method. Three kinds of SG (SG₁, SG₅, and SG₁₀) were prepared by decorating silica with different contents of graphene and were then used to stabilize SA to prepare SA/SG₁, SA/SG₅, and SA/SG₁₀ composites. The structures and thermal energy storage performances of the SA/SG composites were investigated. It is of interest that the thermal energy storage behaviors of the SA/SG composites were dramatically changed with different contents of graphene, presenting more than one endothermal or exothermal peak in the differential scanning calorimetry (DSC) curves while pure SA had only one. The SA in SA/SG₁ and SA/SG₅ showed higher crystallinity (F_c, 84.44% and 84.39%) and greater effective energy storage per unit mass (E_ef, ∼150 J g⁻¹) than that of SA in SA/SG₁₀. These thermal energy storage behaviors and properties were revealed to be related to the pore structures of the SG. The thermal stability of the SA/SG composites was analyzed by a thermogravimetric analyzer (TGA), and the SA/SG composites have good thermal stability. Addition of graphene was beneficial to the enhancement in thermal conductivity of the SA/SG composite, which could reach 0.90 W m⁻¹ K⁻¹, 1.05 W m⁻¹ K⁻¹, and 1.12 W m⁻¹ K⁻¹ for SA/SG₁, SA/SG₅, and SA/SG₁₀, respectively; and were 246%, 304%, and 331% higher than pure SA, respectively. SA/SG₅ has potential for application in thermal energy storage, especially in thermal gradients due to it having both high E_ef and thermal conductivity.