Polyethylene glycol-impregnated carbon quantum dots-phenolic phase change composites for highly efficient thermal energy storage

The development of stable smart thermal energy storage systems is the key to reaching breakthroughs in thermal management technologies based on phase change composites (PCC). In this study, high-performance PCC is developed by impregnating polyethylene glycol (PEG), as a polymeric phase change material (PCM), into the porous structure of modified resorcinol-formaldehyde (RF) hydrogels. Carbon quantum dots (CQDs) and 3-chlorophenol are introduced into the RF structure during the synthesis process to increase energy storage properties and impregnation efficiency. A sol-gel polymerization method is used to synthesize the hydrogels, followed by the impregnation of liquid PEG600 into the hydrogel structure. The low PEG leakage of optimal PCC consisting of 3-chlorophenol and 0.2 wt.% CQDs is related to the presence of surface functional groups in the structure of the modified RF hydrogels resulting in the formation of hydrogen bonding and electrostatic forces. The melting enthalpy of the optimal PCC is 67 % higher than the unmodified RF-based PCC, while the encapsulation efficiency is 92.5 %. Our results confirm that thermal energy storage performance can be improved by 40 % through the addition of CQDs and 3-chlorophenol into the polymeric material. These PCC systems show long-term stability in terms of storage/release cycles and have the potential to be used as thermal regulator systems.