Bioinspired “aerogel grating” with metasurfaces for durable daytime radiative cooling for year-round energy savings

Passive radiative cooling strategy shows a great potential in mitigating global warming and reducing energy consumption. However, existing radiative coolers generally show poor solar-reflection and be easily dampened by environmental aging, making the cooling ineffective. Mimicking the biological design for thermoregulation has given promise for realizing high performance and long time cooling. Here, inspired by structural whiteness in butterflies, we developed a sustainable cellulose nanocrystal aerogel grating (CAG) with designable metasurfaces for efficient radiative cooling, which can be achieved by using copper meshes as well as manipulating the 2D confined freeze casting process. The simulation indicates that the regular tubes and irregular gully on the aerogel surface act as gratings to achieve diffraction and broadband reflection of sunlight. Such CAG exhibits ultrahigh solar reflectance (97.4 %), high infrared emittance (94 %), and anti environmental aging function (anti-ultraviolet light/ contamination). It achieves a sub-ambient temperature drop of 10.5 °C under direct sunlight and still approximately 9.4 °C even after 6 months of exposure to hot weather. Building simulations demonstrate that CAG can save 47 % of the worldwide energy consumption for cooling each year. This work provides insight into the design of bioinspired thermal-regulating materials to save energy consumption.