Thermal Performance and Shape Stability Evaluation of Boron Nitride and Expanded Graphite Synergy in Beeswax‐Based Composite Phase Change Material

Phase change materials (PCMs) are efficient thermal energy storage materials due to their high energy density and ability to maintain a constant temperature during phase transitions. Nonetheless, the low thermal conductivity and liquid phase leakage of PCMs constrain their efficient heat transfer and widespread adoption. The development of leakage‐free composite PCMs with high thermal conductivity remained a challenge. This work presents the first synergistic enhancement of thermal conductivity and shape stability of beeswax PCM with a dual‐scale filler system of h‐BN nanoparticles and EG microparticles that has not been reported previously in the literature. The composite containing 3 wt.% of h‐BN with 10 wt.% of EG exhibited no leakage at 80°C, with a 312% enhancement in thermal conductivity and a 68.5% decrease in light transmittance. Only a minor reduction of ~12% in latent heat was noted in comparison to the base PCM. Further, the composite exhibited comparable performance after 300 thermal cycles.