Effect of Graphene Oxide on Phase Change Materials Based on Disodium Hydrogen Phosphate Dodecahydrate for Thermal Storage

A novel composite phase change material (PCM) for thermal energy storage was prepared by adding graphene oxide (GO) to melted disodium hydrogen phosphate dodecahydrate (DHPD, Na2HPO4·12H2O), which was then impregnated into expanded vermiculite (EV). Because of the addition of GO, the contact angle between melted DHPD and EV was decreased from 56 to 45°. The maximum latent heat of the composite PCM without GO was 167 J/g, which was improved to 229 J/g by adding 0.2 wt % GO. The phase change temperature of the composite PCM was around 42 °C. The results from X-ray diffraction, scanning electron microscopy, and contact angle tests revealed that the improvement in thermal energy storage was achieved because of the reduction of crystal water loss and the increased encapsulation amount of salt hydrates. Thus, the thermal stability of the composite PCM was improved by the addition of GO, which was demonstrated by thermogravimetric analysis. The results of all analyses indicate that the addition of a low weight fraction GO can promote the performance of salt hydrates existing in EV.