Nano-porous carbon-enabled composite phase change materials with high photo-thermal conversion performance for multi-function coating

Scale-up applications in solar energy storage of phase change materials (PCMs) are hindered by the limitation of solid-liquid leakage and lack of light absorption ability. Nano-porous carbon (NPC) with abundant light-trapping structures and high specific surface area was synthesized using attapulgite (ATP) with a rod-like fiber structure as a template and glucose as the carbon source. Novel composite form-stable PCMs (FSPCMs) were then prepared by impregnating stearic acid (SA) into the NPC to solve these limitations via a vacuum impregnation method. Differential scanning calorimetry (DSC) analysis showed that the resulting composite FSPCMs possessed extremely high SA loading capacity (70.5–76.5%) and thermal storage density (160.7–166.5 J/g). Meanwhile, the effect of carbonization temperature on the photo-thermal conversion capacity of composite FSPCMs was studied. Raman and XPS results indicate that the number of carbon defect sites increase with increasing carbonization temperature. These carbon defect sites form the light-trapping structure that can enhance the internal reflection of light, further leading to the excellent photo-thermal conversion capacity of composite FSPCMs. NPC endows the composite FSPCMs with ultrahigh photo-thermal conversion efficiency (up to 94.5%). The composite FSPCMs without a significant change in latent heat enthalpy after 200 melting/freezing cycles implied satisfactory thermal reliability. In addition, a water-based solar heating coating was prepared with composite FSPCMs, which can effectively heat water under sunlight and make the water kept at a comfortable temperature for 21.7 min under no sunlight. Therefore, the prepared composite FSPCMs exhibit a promising application in the novel solar water heating systems.