Dual-functional polyethylene glycol/graphene aerogel phase change composites with ultrahigh loading for thermal energy storage

Abstract

Phase change composites (PCCs) based on polyethylene glycol (PEG) benefit from the encapsulation and restraint of porous supporting network, thus to achieve the results of high loading and no leakage. The graphene aerogel (GA)/PEG composite with ultra-high loading was improved by introducing hydrogen bonds into the traditional GA preparation process to reduce the severe volume shrinkage of GA. In other words, PEG works not only as a phase change matrix, but as hydrogen bond regulator to improve the volume of GA, which realized the dual-function of PEG. The resulting PEG-mediated GA (PGA) with significantly larger volume not only has super high loading as a supporting material, but gives PEG excellent photothermal storage performance as a light absorption enhancer. X-ray diffraction (XRD) results show that the introduction of PEG increases the layer spacing of GA, which is macroscopically reflected in the inhibition of volume shrinkage. The loading percentage increases from 97.56 % to 98.89 %, and the corresponding loading multiple increases sharply from 40-fold to 89-fold, which is the highest loading known based on PEG4000 as PCM. Higher loading means higher phase transition enthalpy retention. The melting enthalpies of P-GA and P-PGA are 177.92 J/g and 183.47 J/g, and the relative enthalpy efficiency is as high as 98.12 % and 99.82 %, respectively. Simultaneously, both of them have good thermal stability and cyclic stability, photothermal conversion and heat storage capacity efficiency is about 77.97 % and 85.89 %, respectively. All characterization results show that the prepared ultra-high loading PCCs further enhance the utilization of low-grade heat energy.