Preparation and performance study of porous biochar-based shape-stabilized phase change materials for thermal energy storage

The reasonable utilization of waste biomass can contribute to the energy system. In this study, waste melon-seed shells were used as raw materials to prepare porous biochar (MSB) as the support skeleton and thermal conductive additive for stearic acid (SA), thereby improving the thermal conductivity of the SA and solving the issue of their melting leakage. Melon-seed shell biochar-based composite phase change materials (MSB-PCMs) were prepared through melt blending and compression molding. The research shows that MSB, synthesized at a pyrolysis temperature of 600 degrees C, exhibited a three-dimensional porous structure along with two-dimensional sheet-like morphology which facilitated additional heat transfer pathways within SA. When incorporating 25 wt% of MSB into the SA (MSB-PCM5), the thermal conductivity was significantly enhanced in the resulting MSB-PCM5 by up to 287.22%. Moreover, the phase change process remained leak-free without deformation, and the latent heat value only deviated from theoretical values by a margin of 0.88%. Heat response tests demonstrated that heating and cooling times for MSB-PCMs outperformed those for pure SA; specifically, a reduction in heating time by 19.5% and cooling time by 31.77% was observed for MSB-PCM5. Comprehensive evaluation after subjecting them to 200 cycles of melting-solidification tests indicated excellent shape stability and thermal performance for MSB-PCMs. Therefore, porous biochar, as a supporting skeleton and thermal conductivity additive of phase change materials, has great potential in phase change energy storage applications.