Comparative Study of Single-Walled Carbon Nanotubes and Graphene Nanoplatelets for Improving the Thermal Conductivity and Solar-to-Light Conversion of PEG-Infiltrated Phase-Change Material Composites

More attention has been given to studies on the synchronous enhancement of the light-to-thermal conversion capacity and thermal conductivity of polymer phase-change material (PCM) to conserve solar energy. Here, commonly used PEG PCM was encapsulated by graphene nanoplatelets (GNPs) and single walled carbon nanotubes (SWCNs), while polymer composites were simultaneously obtained. The 3D interconnected SWCNs and GNPs equipped PEG with (1) shape stability and thermal durability, (2) negligible change in energy storage density, (3) record-high thermal conductivity, and (4) favorable solar-to-thermal conversion capability as expected. In clear contrast to PEG/SWCNs embedded with 8 wt % SWCNs, PEG/GNPs with only 4 wt % GNPs showed comparable performance: (1) 96% of the thermal energy storage capacity of neat PEG, (2) more than 12-fold the thermal conductivity of the neat PEG, and (3) excellent solar-to-thermal conversion efficiency of 86%. We quantify these differences for the first time. More importantly, the involved microstructure performance mechanism of these photodriven composite PCMs has been discussed and visualized for the first time. The superior comprehensive performance of PEG/GNPs compared to that of PEG/SWCNs could be attributed to the filler dimension difference, which follows the trend of 1D < 2D.