Largely enhanced thermal conductivity of poly (ethylene glycol)/boron nitride composite phase change materials for solar-thermal-electric energy conversion and storage with very low content of graphene nanoplatelets

Phase change materials (PCMs) with high thermal conductivity and efficient solar energy conversion have recently attracted much attention. However, a facile strategy to enhance thermal conductivity and realize energy conversion and storage is still eagerly desired. In this work, a very low content of graphene nanoplatelets (GNP) is introduced into poly (ethylene glycol) (PEG)/boron nitride (BN) composite PCMs, resulting in great improvement in thermal conductivity and photoabsorption ability via a facile solution blending process. The presence of GNP contributes to enhancing thermal conductivity and realizing efficient solar energy conversion (including solar-to-thermal and solar-to-electric energy conversion) for the PEG/BN/GNP composite PCMs owing to the formation of improved BN/GNP thermally conductive network and the improvement of sunlight harvesting ability, respectively. Thermophysical properties demonstrate that compared with PEG/BN composite PCMs at the same BN content, PEG/BN/GNP composite PCMs containing a low GNP content maintain comparable energy storage density. The study sheds light on the realization of solar energy utilization and storage of the organic PCMs requiring high thermal conductivity.