Comparative Study of Carbon Nanoparticles and Single-Walled Carbon Nanotube for Light-Heat Conversion and Thermal Conductivity Enhancement of the Multifunctional PEG/Diatomite Composite Phase Change Material

We report two novel 3-dimension hierarchical diatomite struts by filling the diatomite pores with a small amount of single-walled carbon nanotubes (SWCNs) and carbon nanoparticles (CNPs). The emerging supporting scaffolds are then applied to a prepare polyethylene glycol (PEG)-infiltrated composite phase change material to seek an efficient but easy way to improve the thermal conductivity and synchronously accomplish the light-thermal conversion on the one hand. On the other hand, the mechanism of the microstructure-performance relationship of these composites has also been briefly presented and compared. In addition, the involved differences and synergistic effects between the diatomite and carbon filler have been quantified and visualized for the first time. Compared with CNPs, the SWCNs with the same content inside diatomite pores enable a much more packed architecture and faster thermal conductive route, light harvesting ability, form stability, and comparable energy storage density. Obviously, the superior comprehensive performance of PEG/DCNs can be attributed to the filler dimension discrepancy trend of 0D < 1D. Compared to PEG/Dt, the thermal conductivity of the PEG/diatomite/SWCNs (1.52 W/m K) increases by nearly 5.2-fold (∼424% increase) upon ∼3.2 wt % SWCN addition along with an unexpected rise in the energy storage density of ∼12.1%. To the best of our knowledge, this is the first study on the light-thermal conversion behavior of mineral-based composites, let alone using diatomite, which provides critical insights to design the high performance energy storage composites for domestic solar hot water supply systems.