Highly Aligned Porous Nanocomposite Aerogels with Anisotropic Thermal Conductivity for Sub-Ambient and Above-Ambient Radiative Cooling

Abstract

Scalable and cost-efficient porous structural materials, characterized by their thermal insulation and solar scattering properties, hold significant promise as radiative cooling solutions for zero-energy thermal regulation of objects subjected to sunlight and high temperatures. However, the intrinsic thermal insulation restricts their capacity to effectively dissipate excess internal heat, thereby limiting their applicability in cooling scenarios within above-ambient enclosed environments. Herein, a directional freeze-casting strategy is presented for preparing a highly aligned porous nanocomposite aerogel. This aerogel demonstrates a thermal anisotropy factor of 3.48, indicating a markedly enhanced thermal conductivity in the axial direction ascribing to the dual orientation of the aligned skeletal walls and the space-confined arrangement of thermally conductive nanosheets. This aerogel also demonstrates a high solar reflectance of 95.3% in the axial direction facilitated by the design of hierarchical pore structures and the backscattering properties of the embedded 2D nanosheets. Consequently, this aerogel functions effectively as a multi-scenario radiative cooler, achieving temperature reductions of 3.3 and 15.9 °C for cooling sub-ambient and above-ambient enclosed environments exposed to sunlight and high temperatures. This study significantly expands the applicability of porous structural materials in multi-scenario radiative cooling, addressing the limitations of conventional porous materials in cooling heat-generating enclosed environments.