Aramid Nanofiber@Al2O3 Composite Aerogels toward Ultra-High Near Infrared Transmittance and Low Thermal Conductivity for Robust Passive Thermal Managements

Abstract Aramid nanofiber (ANF) aerogels possess excellent flexibility and favorable mechanical properties. However, their limited infrared transmittance, relatively high thermal conductivity, and low flame retardancy significantly restrict their application in passive thermal management. In this study, a microphase separation strategy is employed to fabricate ANF@Al₂O₃ composite aerogels, enabling a structural transition from a uniform-pore to a slit-pore morphology. Benefiting from the light regulation by the slit pore structure and the flame-retardant effect of Al₂O₃, the prepared ANF@Al₂O₃ aerogels material have ultra-low thermal conductivity (≤30 mW/(m·K)), high infrared transmittance (near-infrared transmittance >90%), and excellent fire resistance (enhanced combustion endurance), which is able to meet the various needs of passive heating in intelligent buildings. Under outdoor solar irradiation (29.3 °C, 677.6 W/m²), the ANF@Al₂O₃ composite aerogel achieves an internal temperature of 50.46 °C, corresponding to a passive heating efficiency of 72.22%. This study provides a strategy for designing high-performance composite aramid aerogels and holds great promise for applications in energy-efficient buildings, aerospace thermal insulation, and smart thermal management systems.