Metal Nanoparticle–Carbon Matrix Composites with Tunable Melting Temperature as Phase-Change Materials for Thermal Energy Storage

Phase-change materials with tunable melting temperature provide a new design for thermal energy storage applications. Here, we demonstrate a general one-pot synthesis of composites containing ligand-free metal nanoparticles (Bi or Pb) distributed in a mesoporous carbon matrix as form-stable phase change materials. The melting temperature of the encapsulated metal nanoparticles (NPs) can be tuned as a function of particle size, which depends on the metal loading in the composite material. Melting and resolidification temperatures are stable through multiple melt–freeze cycles. The carbon matrix encapsulating the metal NPs prevents aggregation of the NPs, accommodates volume change, and prevents leakage during phase change process. The melting temperature of the Bi NPs decreases by 33 °C compared to the melting point of bulk Bi with a Bi loading of 48 wt % in the composite materials, and that of Pb NPs decreases by 18 °C compared to bulk Pb with a Pb loading of 47 wt %. Using transmission electron microscopy, we also demonstrate that the porous channels of the carbon matrix serve as containers for the melted Pb NPs.