Poly(ethylene glycol)-grafted nanofibrillated cellulose/graphene hybrid aerogels supported phase change composites with superior energy storage capacity and solar-thermal conversion efficiency

The development of organic phase change materials (PCMs) with large energy storage capacity, high thermal conductivity, and satisfactory solar-thermal conversion performance is critical for large-scale solar energy utilization. Here, novel composite PCMs based on poly(ethylene glycol) (PEG), nanofibrillated cellulose (NFC), and graphene were successfully fabricated by impregnating PEG into PEG-grafted NFC/graphene hybrid aerogels (GA/NFC-g-PEG). The GA/NFC-g-PEG with three-dimensional interconnected porous structures well supported the PEG within the nanostructural frameworks and effectively prevented the leakage and diffusion of PEG above its melting point. Grafting of PEG onto NFC was performed to improve the affinity between PEG and NFC/graphene hybrid aerogels, which significantly increased the PEG loading capacity of the CNF-g-PEG/graphene aerogel and prevented the leakage of PEG. Differential scanning calorimetry result showed that the as-prepared composite PCMs possessed extremely high melting enthalpies ranging from 185.5 to 187.4 J/g. The hot stage-digital camera test and thermogravimetric analyses showed that the composite PCMs exhibited excellent form-stability and thermal stability. Moreover, the introduction of graphene significantly increased the thermal conductivity and solar-thermal conversion efficiency of the composite PCMs. In conclusion, the synthesized composite PCMs showed tremendous potential for thermal energy storage applications.