Constructing anisotropic conical graphene aerogels with concentric annular structures for highly thermally conductive phase change composites towards efficient solar–thermal–electric energy conversion

Abstract

Although organic phase change materials can reversibly store and release latent heat during their phase change processes, their weak solar–thermal conversion ability, low thermal conduction, and poor structural stability seriously hinder their applications for solar–thermal energy conversion as well as thermal energy utilization. Herein, anisotropic high-quality conical graphene aerogels (HCGAs) with concentric annular structures are constructed to enhance thermal conduction, solar–thermal energy conversion, and shape stability of phase change materials for solar–thermal–electric energy conversion applications. By regulating the orientation of graphene oxide liquid crystals, the resultant graphene sheets are aligned from the apex to the bottom of the cone, providing efficient heat transfer along the vertical direction of the phase change composites. An optimal HCGA/tetradecanol phase change composite with 7.05 wt% of graphene achieves a high through-plane thermal conductivity of 4.54 W m⁻¹ K⁻¹ with a high latent heat of 206.1 J g⁻¹. Benefiting from the larger solar light-absorption surface than conventional square/cylindrical phase change composites and the rapid heat transfer of the anisotropic high-quality graphene conduction network, the conical phase change composite achieves a high solar–thermal energy conversion and storage efficiency of 84.0%. Furthermore, a solar–thermal–electric generator is assembled with the conical phase change composite array, exhibiting maximum output voltages of 261 and 1214 mV under solar light intensities of 100 and 500 mW cm⁻², respectively. Even after the removal of the solar light, the voltage output can still be continued by releasing the stored thermal energy.