Fabrication and Characterization of Multi‐Walled Carbon Nanotubes/Graphene Nanoparticles Reinforced Microencapsulated Composite Phase Change Materials for Thermal Energy Storage Applications

This work presents the development of microencapsulated composite phase change materials (MECPCMs) designed to improve thermal energy storage (TES) performance and heat transfer capability through an in situ polymerization method. Paraffin served as the latent heat storage core, enclosed within a urea–formaldehyde shell, followed by the incorporation of multi‐walled carbon nanotubes (MWCNTs) and graphene nanoparticles (GNPs) as reinforcing agents. The resulting microcapsules ranged in size from 7.79 to 25.32 µm, depending on filler type and concentration. MWCNTs‐based capsules exhibited average diameters of 17.40, 23.01, and 16.74 µm, whereas GNPs‐based systems measured 25.32, 12.05, and 7.79 µm. The base microcapsules achieved an encapsulation ratio of 97.9%, efficiency of 96.2%, and energy storage of 98.28%. After nanoparticle addition, energy storage remained above 98%. Thermal conductivity increased from 0.2 W/m·K (pure paraffin) to 0.229 W/m·K after encapsulation (14.5%). With 5 wt% MWCNTs, it reached 0.789 W/m·K (294.5%), while GNPs achieved 0.558 W/m·K (179%). The improvement is linked to the formation of a conductive network, which accelerates phase transitions. MECPCM‐3 showed optimal performance, with 94.7% encapsulation efficiency and 98.32% energy storage capacity. Overall, these findings confirm that integrating carbon nanoparticles into microcapsules offers strong potential for developing advanced, efficient, and high‐performance TES systems.