Modification of microencapsulated phase change materials(MPCMs) by synthesizing graphene quantum dots(GQDs) and nano-aluminum for energy storage and heat transfer applications

MPCMs and their suspensions, acting as the thermal storage, heat transfer or temperature constancy mediums, have gained concerns in various energy related sectors. However, problems involving high supercooling degree, low thermal conductivity and suspensions instability are barriers for their energy storage applications. The present study focuses on such properties by adding GQDs/nano-aluminum into MPCMs particles. Paraffin was selected as core material and urea melamine formaldehyde polymer as shell to prepare 10 MPCMs samples (no modifiers, GQDs, nano-aluminum, GQDs & nano-aluminum) via in situ polymerization. The morphology, thermal conductivity, thermal property and MPCM/suspensions stability were characterized. It was found, the selected modifiers didn't impact on the microcapsules morphology, but GQDs can make particle size smaller and distribution more uniform. Adversely, the mean particle size can be increased by nano-aluminum. GQDs are much more effective than nano aluminum in improving thermal conductivity. GQDs can suppress supercooling effectively, however, nano-aluminum has no obvious effect on supercooling suppression. The MPCMs suspension modified by the selected amount of GQDs and nano-aluminum (Al-GQDs(4.5-2)) achieved a high physical stability. No structure instability of modified MPCM sample was observed. To sum up, the combined effort of GQDs and nano-aluminum enabled MPCMs to be more applicable in energy storage applications. (C) 2019 Elsevier Ltd. All rights reserved.