Abstract: Energy as a symbol of human civilization has a profound impact on human life. Fossil fuels, including coal, oil, and natural gas are still the most demanded and consumed energy sources in the world due to the worldwide economic expansion and population explosion. Thermal energy storage can not only alleviate the mismatch between energy supply and demand, but also improve the reliability of energy systems and the efficiency of thermal energy utilization. The thermal energy storage methods mainly include sensible heat storage and latent heat storage. Compared with sensible heat storage, latent heat storage has a much higher energy storage density. At present, phase change materials (PCMs) are widely used in solar heating systems, energy-saving buildings, air conditioning systems, and other fields. However, the practical application of PCMs has been limited by several persistent problems in various fields, such as the unstable shape of molten state, low thermal conductivity, and weak interface bonding of supporting materials. Therefore, to effectively solve the leakage problem and increase the thermal conductivity of composite PCMs, we seek porous materials with a high thermal conductivity as supports. In recent years, carbon-based materials derived from biomass have attracted extensive attention due to their excellent properties such as large specific surface area and adjustable porous structure. In this study, an eggplant-derived porous carbon material (HBPC) was prepared by hydrothermal synthesis, and another porous carbon material (biomass-derived porous carbon, BPC) was prepared by direct pyrolysis of eggplant. After that, PEG/HBPC and PEG/BPC composite PCMs were prepared by a vacuum-impregnated method using HBPC and BPC as supporting materials and polyethylene glycol (PEG2000) as PCMs. Their structure and performance were characterized by SEM, Raman spectroscopy, Mercury intrusion method, Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetric (TG) analysis, and differential scanning calorimetry (DSC). The results show that PEG/BPC PCMs composite obtained by direct pyrolysis have a better energy storage effect, the mass fraction of PEG load is up to 90.60%, and the latent heat of melting is 133.98 J·g⁻¹. At the same time, PEG/BPC composite is proved to be a shape-stable PCM with long-term stability.