Ultrathin graphite sheets stabilized stearic acid as a composite phase change material for thermal energy storage

Ultrathin graphite sheets (UGSs) were stripped directly from natural flake graphite (FG) through a coupled ultrasonication-milling (CUM) process followed by a shear-assisted supercritical CO2 (SSC) stripping. As-prepared UGSs were centrifuged (3500 and 5000 rpm) to support stearic acid (SA) to produce SA/UGSs. Characterization results proved UGSs was stripped from natural FG. Structural and morphological characterization demonstrated that the UGS-5000 had a layer thickness was about 3.4-4.2 nm, significantly thinner than that of natural FG. Raman spectra and TG-DSC analysis showed UGS-5000 have more structural defects than other UGSs, and could accommodate a SA loading capability of 171.5%. FTIR and XRD analysis indicated that no chemical reaction had occurred between SA and UGSs during impregnation. All samples had a good thermal stability below 180 °C, with the endothermic phase change peak being recorded between 53.60 and 53.12 °C range, and the melting and freezing enthalpies of SA/UGS-5000 were 113.7 and 112.9 J g-1, respectively. After 50 thermal cycles, it could keep a great thermal reliability and has a thermal conductivity of 10.08 times higher than that of pure SA. These results demonstrate that SA/UGS-5000 have potential in thermal energy storage applications including cooling, building energy efficiency and solar thermal storage.