Synthesis and properties of shape-stabilized composite phase change material based on biochar via molten salt thermal treatment

To address the challenges of liquid leakage and low thermal conductivity in phase change materials (PCMs), this study synthesis high-performance shape-stable composite PCMs (ss-CPCM) using activated biochar (AC) derived from a molten salt thermal treatment as the support material. Biomass was carbonized and simultaneously activated in a NaOH/Na₂CO₃ mixed molten salt system, yielding AC with an high specific surface area (2491.6 m²∙g⁻¹), large pore volume (1.334 cm³∙g⁻¹), uniform meso-micropores (∼2 nm), good thermal transfer performance (7.045 W∙m⁻¹∙K⁻¹) and abundant hydroxyl groups. 1-Tetradecanol (TD) was selected as the PCM and incorporated into the AC via vacuum impregnation. The ss-CPCM exhibited a high PCM loading ratio (80 %), large latent heat capacity (164.99 kJ∙kg⁻¹) and excellent cyclic stability, retaining 93.81 % of its latent heat after 100 cycles. Meanwhile, thermal conductivity was raised by 21.9 % and 456.4 % at 25 °C and 35 °C, respectively. Theoretical calculations such as DFT, ESP, and IGMH analysis were employed to elucidate the loading mechanism and visualize the weak interactions between PCM and AC. This work presents a scalable and energy-efficient strategy for constructing carbon-based ss-CPCM with outstanding thermal conductivity and reliability, offering strong potential for low-temperature thermal energy storage applications in solar thermal utilization.