Synergistic enhancement of phase change materials through three-dimensional porous layered covalent triazine framework/expanded graphite composites for solar energy storage and beyond

The challenges of leakage and low thermal conductivity have emerged as obstacles that hinder the advancement of long-term thermal stability and versatility of phase change material (PCM). This study aims to address the challenges of high leakage rate and low thermal conductivity associated with paraffin wax (PW) in phase change energy storage. A composite PCM with a layered microstructure was successfully synthesized by physically blending expanded graphite (EG), covalent triazine framework (CTF), and adsorbed PW. For the first time, the encapsulation of PCMs using covalent organic frameworks (COF) was realized. Subsequently, various aspects of the prepared materials were thoroughly characterized and analyzed, demonstrating excellent performance. The material exhibited a leakage rate of only 0.18 %, a thermal conductivity approximately 10 times higher than that of pure PW, and a high latent heat of phase change (111.26 J/g). After undergoing 500 thermal cycles of storage and release, the latent heat of phase change remained stable at around 72 %, indicating robust thermal cycle stability. Furthermore, photothermal tests revealed an impressive photothermal conversion efficiency of 86.9 % for the composite PCM, highlighting its remarkable photothermal conversion capability and efficiency. This study provides an innovative solution to the challenges of high leakage rate and low thermal conductivity in paraffin-based phase change energy storage. Additionally, it delivers valuable theoretical guidance and an experimental foundation for the development of more efficient and stable PCMs.