Eco-friendly biochar/CNTs-enhanced myristic acid composite phase change materials for efficient solar-thermal energy conversion

In the paper, we crafted a unique eco-friendly composite phase change material (PCM) with superior leak-proof performance by integrating modified biochar, carbon nanotubes (CNTs) of specific diameters, and myristic acid (MA) through a vacuum impregnation process. The biochar was modified with KOH, resulting in a specific surface area of 813.56 m 2 /g for modified biochar (KBC3) and an increased MA loading capacity of 63 %. Various characterizations confirmed the successful incorporation of MA into the porous materials without destroying their structure. To further enhance the PCM’s loading capacity and leakage resistance, CNTs of varying diameters were added to the KBC/MA PCM. With 75 % MA loading, KBC1.5/MA (75) showed significant shape leakage (8.5 % mass loss). However, KBC1.5/CNT1/MA (75) exhibited minimal leakage during testing, indicating improved leakage resistance. Notably, KBC1.5/CNT2/MA (75) exhibited high thermal conductivity enhancement (40.1 %), a high enthalpy of phase change at 143.5 J/g, outstanding enduring durability, and consistent thermal cycling curve after 50 cycles compared to single DSC curve. Biochar modification and CNTs significantly boosted the photothermal conversion efficiency of PCMs, from 0 % in pure MA and BC/MA (63) to 58.88 % in KBC1.5/MA, and further to 76.37 % in KBC1.5/CNT2/MA (63). The addition of CNTs with appropriate diameters had a profound impact on enhancing the PCMs’ performance, primarily due to carbon nanotubes’ high thermal conductivity and strong visible light absorption capabilities.