Thermal conductivity enhancement utilizing the synergistic effect of carbon nanocoating and graphene addition in palmitic acid/halloysite FSPCM

Abstract Phase change material (PCM) based thermal storage technology can help mitigate the increasing energy problems caused by the rapid economic developments and population growth. However, the extremely low thermal conductivity of PCM has substantially impeded their wide applications in practice. Therefore, this study has developed a novel palmitic acid (PA)/halloysite nanotubes (Hal) form-stable PCM (FSPCM) with enhanced thermal conductivity utilizing the synergetic effect of carbon nanocoating and graphene addition. To enhance the thermal conductivity of the Hal, the C-Hal (CH) was firstly prepared through sucrose decomposition, and the effect of calcination temperature and sucrose concentration on the CH were systematically investigated for identifying the optimal carbonization condition. Then, the obtained CH was used to encapsulate PA by a low-cost and facile direct impregnation method, and the leakage test was implemented to identify the loading of the FSPCM. Meanwhile, graphene was added to further improve the thermal conductivity of the FSPCM. Finally, the critical thermal, microstructure, and chemical compatibility properties of as-prepared PA/CH/graphene FSPCM were systematically investigated. The study results indicated that the FSPCM exhibits melting temperature at 62.89 °C with a thermal energy storage density of 71.35 J/g and desirable thermal reliability. More importantly, the thermal conductivity of the prepared FSPCM has been substantially improved up to 1.51 W/mK, which is 3.60 times that of pristine PCM. The main reason is that the synergistic effects of carbon nanocoating and graphene addition have built a continuous highway for heat transfer. The study provides a practical means to greatly improve the thermal conductivity of the FSPCM, thereby promoting its practical applications.