Fe catalytic graphitisation to prepare biomass derived graphitic matrix based composite phase change materials for photothermal conversion and storage

Low thermal conductivity is one of the key defects of pristine phase change materials (PCMs) for solar thermal energy storage. Biomass derived carbonaceous matrix, which could be recycled from wide sources, are favourable to incorporate with PCMs for solar thermal storage applications for their highly porous structure and decent thermal properties. Their unique structures get from the grown plants also endue them with diverse properties and functions, such as anisotropic thermal properties for directional heat transfer. However, direct pyrolysis of biomass generally produces amorphous carbonaceous structure that suffers insufficient thermal conductivity. Therefore, this work proposed a simple, rapid, and effective Fe graphitisation route to derive pine wood as graphitic matrix to synthesize multifunctional shape stabilized composite PCM. The Fe graphitisation process has induced the conversion of amorphous carbon to well-ordered graphitic structure. Further elevating the catalytic temperature contributes to a high graphitisation degree up to 89.53 %. With this Fe graphitisation route, the thermal conductivity of PCM composite at its longitudinal direction has increased from 0.545 W · m −1  K −1 to 1.846 W · m −1  K −1 . The solar absorptivity has reached up to 95.60 %. Besides, a high amount of PCM (∼72.26 wt%) was retained by the matrix, offering a high endothermic enthalpy up to 154.2 J/g. In the meantime, the aligned tubular structure of graphitic matrix leads to an anisotropic heat transfer behaviour, displaying a greater thermal conductivity along the longitudinal direction. Therefore, this study has provided a new approach to fabricate high-performance biomass derived graphitic matrix based PCM composite for solar thermal storage applications.