Multi-interfacial engineered waste cardboard aerogels enabling high thermal storage density and solar-driven temperature regulation in buildings

Form-stable phase change materials (PCMs) are vital for building energy conservation, yet balancing thermal storage density, leakage prevention, and photothermal conversion remains challenging. Herein, a high-energy-density, solar-driven composite PCM was fabricated by upcycling waste cardboard into a robust 3D aerogel skeleton. The skeleton was cross-linked via sodium alginate/Ca 2+ and functionalized with carbon nanotubes (CNTs) using sodium carboxymethyl cellulose (CMC Na) as an interfacial binder, followed by vacuum impregnation of eicosane (EI) and polydimethylsiloxane (PDMS) coating encapsulation. The optimized composite exhibits an exceptional melting enthalpy of 201.86 J/g and robust thermal reliability (2.3% enthalpy loss after 200 cycles). Benefiting from multi-interfacial engineering, the internal capillary network and external PDMS barrier synergistically eliminate liquid leakage even at 60 °C for 2 h, while imparting outstanding water resistance and flame retardancy. Furthermore, the continuous CNT network ensures excellent thermal conductivity (0.39 W/(m·K)) and rapid photothermal conversion response. In simulated building tests, the composite roof effectively regulates indoor temperature, achieving a substantial indoor-outdoor temperature gradient of up to 23 °C and a significant thermal lag compared to a standard wooden roof. This work offers a sustainable, multifunctional paradigm for solid waste upcycling and high-performance building thermal management.