Bilayer-Structured Passive Radiative Cooling Coating with Thin Thickness, Highly Scattering, and Enhanced Thermal Dissipation

Passive daytime radiative cooling (PDRC) is a new thermal management solution that does not rely on external energy sources. Traditional PDRC materials have a relatively high thickness (typically 500-800 μm), which prevents efficient cooling and limits their application scenarios. To address this challenge, we propose a bilayer porous structure that meets the application needs of different scenarios (both below-ambient and above-ambient temperatures). This structure is formed through the synergistic assembly of inorganic dielectric particles using natural sedimentation and phase separation techniques, addressing the conflict between cooling performance and material thickness. Due to the bilayer porous structure, the coatings exhibit sufficient solar reflectance (98.59 ± 0.71%), atmospheric emissivity (95.15 ± 0.53%), and relatively high thermal conductivity (1.203 W·m^-1·K^-1) with a thickness of only 220 ± 15 μm. Field tests demonstrate below-ambient cooling of 4.25 °C and above-ambient cooling of 15.67 °C under intense solar radiation, while this bilayer porous PDRC coating exhibits impressive durability and energy efficiency. This work provides a novel coating construction strategy, showing great potential to advance energy-free cooling materials toward real-world applications.