Polyethylene glycol phase change material embedded in a hierarchical porous carbon with superior thermal storage capacity and excellent stability

Abstract Hierarchical porous materials are recommended to trade off the mismatch between high loading and efficient crystallization in pore-based composite phase change materials (PCMs), coupling the functions of expanded pores (mesopores and macropores) along with maintained micropores. Hierarchical porous carbon (HPC) was successfully synthesized from metal organic framework MOF-5 with a large specific surface area (1345 m2/g) and high pore volume (2.69 cm3/g). The adsorption capacity of HPC for low temperature PCMs, polyethylene glycol (PEG) and stearic acid (SA) reaches over 90 wt%. The introduction of HPC has very little impact on the crystallinity of the PCMs, as a result, the composites possess similar high thermal storage capacity to pure PCM. The as-prepared composites efficiently perform heat store and release with reasonable reliability. Moreover, the supercooling of PCM was strongly suppressed due to the large surface area of HPC. Molecular dynamics (MD) simulation confirms that the smaller pores enable a stronger force of the carbon skeleton on the PCM, which ensures effective anchoring of the PCM. Simultaneously, those larger pores provide enough space for storage of PCM, with a reduced negative effect on its crystallization. After the compounding, the phonon vibration matching between guest and host is strengthened, which is beneficial to the transfer of energy thus receives an enhanced thermal conductivity. Our research demonstrates the great potential of using hierarchical porous skeleton to immobilize phase change materials for practical thermal storage.