Superdurable, Flexible Ceramic Nanofibers for Sustainable Passive Radiative Cooling

Passive daytime radiative cooling can mitigate global warming but requires durable and resilient materials for real-world applications. Here, a robust superhydrophobic ZrO2-Al2O3 nanofiber (sh-ZANF) membrane is fabricated via electrospinning followed by fluorine-free surface modification. Optically engineered sh-ZANF attains an extremely high solar reflectivity of 97.7% due to strong scattering at numerous fiber/air interfaces with a high refractive index contrast (nfiber = 2.04, nair = 1). sh-ZANF also possesses a high atmospheric transparency window emissivity of 95.6% originating from phonon-polariton resonances of abundant Al-O/Zr-O bonds without a strong Reststrahlen effect. The optimal sh-ZANF membrane demonstrates subambient cooling of 6.6 °C and a maximum cooling power of 125 W/m2 under 817 W/m2 solar irradiance. Coverage by sh-ZANF cools building models, automobile models, and hand-held cameras under sunlight by 14.7 °C, 16.8 °C, and 11.1 °C, respectively. Equipping buildings with sh-ZANF is estimated to save more than 10 MJ/m2 annually and reduce CO2 emission by up to 27%. Moreover, these all-ceramic nanofibers can withstand temperatures exceeding 1400 °C, safeguarding buildings and their occupants during fire emergencies. Our sh-ZANF also displays attractive self-cleaning properties and successfully passes accelerated environmental aging tests, suggesting its applicability for future energy-efficient and sustainable cooling strategies.