Multifunctional phase change composites based on sugarcane-derived honeycomb-like carbon and halloysite coating for efficient thermal management and tri-modal energy conversion

The practical application of organic phase change materials (PCMs) like polyethylene glycol (PEG) is limited by leakage, low thermal conductivity, and lack of active energy-harvesting capability. To address these challenges, a multifunctional composite PCM (PEG@HCS-85) was fabricated through a stepwise strategy. PEG was first encapsulated within a conductive, honeycomb-like carbonized sugarcane (CS) skeleton, followed by coating with a halloysite nanotube (HNT)/polyvinyl alcohol (PVA)/polypyrrole (PPy) film via rapid freezing. The CS framework provides shape stability, enhances thermal conductivity (0.483 W m −1  K −1 ), and enables efficient electro-thermal conversion via Joule heating. The HNT/PVA/PPy coating ensures excellent leakage resistance (100 wt% retention after heating at 100 °C) and boosts broadband solar absorption (98.0% average absorbance), leading to a high photothermal conversion efficiency of 96.48%. Moreover, when integrated with a thermoelectric generator (TEG), PEG@HCS-85 serves as a thermal buffer that stabilizes the temperature gradient, enabling sustained power generation even after illumination ceases (maximum power density 33.9 W m −2 under 3 kW m −2 with water cooling). The composite also exhibits good thermal cycling stability after 1000 cycles. This work demonstrates a rational design of a biomass-based, multifunctional PCM that combines efficient thermal storage with active multifunctional energy conversion, offering promising potential for solar thermal management, waste heat recovery, and round-the-clock renewable energy utilization.