A vertically aligned anisotropic boron nitride nanosheet (BNNSs)/polyvinyl alcohol (PVA) composite aerogel with ultra-low thermal conductivity prepared by the prefreeze-freeze-drying method for efficient thermal management

Thermal management plays a critical role in contemporary engineering and materials science, finding applications in diverse fields such as electronics and aerospace. Three-dimensional (3D) aerogels have gained popularity as a promising alternative to traditional insulation materials due to their high porosity and remarkably low thermal conductivity. In this study, we propose a novel method for fabricating a composite aerogel comprising vertically aligned anisotropic boron nitride nanosheets (BNNSs) and polyvinyl alcohol (PVA) using the prefreeze-freeze-drying technique. The resulting composite aerogel exhibits exceptional thermal insulation properties, characterized by an ultra-low thermal conductivity of 22 mW/mK (transverse) and 71 mW/mK (axial). These values are significantly lower than those of conventional aerogels and most other polymer composites. The anisotropic thermal behavior of the composite aerogel can be attributed to the vertically aligned BNNSs. Additionally, the composite aerogel demonstrates remarkable thermal stability and favorable mechanical properties. It also exhibits excellent electrical insulation and flame retardant properties, along with a unique capacity for heat storage and utilization. Furthermore, outdoor testing reveals that the composite aerogel exhibits a maximum heat storage temperature of 3.8 °C higher than the ambient temperature, thereby showcasing its exceptional thermal insulation performance and distinct capability for heat storage and utilization.