Flexible radiative cooling material based on amorphous alumina nanotubes

With the rapid development in near / far field thermal radiation and micro- / nano- fabrication, passive radiative cooling has become an intriguing topic in both fundamental scientific research and practical energy engineering. In this paper, we use Amorphous Alumina Nanotubes (AANs) to prepare a flexible material for high-efficient daytime radiative cooling. Instead of applying parallel nanotube array or total randomly distributed nanotubes, we experimentally fabricated a porous membrane by introducing hexagonal lattice roots at the bottom and random agglomeration at the top for AANs. Near-unity emissivity originated from alumina absorption and complex scattering inside the membrane covers the 8-13 µm atmosphere window. Under direct sunlight, the flexible AANs membrane achieves a theoretical net cooling power of 71.0 W/m 2 , leading to an experimental maximum temperature reduction of 6.7 °C to the ambient air. Our material paves herein a way for producing low-cost and efficient flexible daytime radiative coolers.