Phase change nanocapsules incorporated with nanodiamonds for efficient photothermal energy conversion and storage

Phase change nanocapsules exhibit significant potential in harnessing photothermal energy to address the ever-growing energy demand; however, their application is restricted by limited solar absorption capacity and low thermal conductivity. In this study, nanodiamonds (NDs) were firstly incorporated with phase change nanocapsules to solve these issues owing to their broad light absorption range and exceptionally high thermal conductivity. Phase change nanocapsules composed of n-Octadecane core and ND/SiO2 shells were successfully synthesized through the miniemulsion polymerization method. The morphologies, chemical composition, phase change properties, thermal conductivities, and thermal stabilities of the phase change nanocapsules were comprehensively analyzed. The phase change nanocapsules exhibited a significantly high latent heat of 128.22 J/g, coupled with exceptional leak-proof performance. Notably, the nanocapsules exhibited a high thermal conductivity of 0.747 W/m·K, which was more than 5 times compared to the pristine n-Octadecane. Furthermore, the incorporation of NDs significantly enhanced the light absorption capacity of the nanocapsules, resulting in an impressive photothermal conversion efficiency of up to 92.1%. The mechanism of the enhancement was primarily attributed to the thermal vibrations of molecules within NDs as well as the optical confinement effects provided by ND/SiO2 hybrid shells. Our study presents a facile strategy for simultaneously enhancing the photothermal energy conversion and storage performance of phase change capsules, which hold tremendous potential for solar energy utilization applications in the future.