Passively Cooled Paint‐Like Coatings for Atmospheric Water Capture

Abstract Atmospheric water capture has the potential to alleviate water scarcity around the world and works by condensing water vapor onto a cold surface. However, actively cooling a surface requires substantial energy. The application of large scale (20 × 20 cm ² ) porous poly(vinylidene fluoride‐cohexafluoropropene) (PVDF‐HFP) coatings is reported with ultra‐high total solar reflectance (96%) and emittance (95% in the atmospheric window), which can passively cool 6°C below ambient temperature when exposed to the sky, even under direct sun. When the coating cools below the dew point, it harvests water from the atmosphere through condensation of droplets. Thanks to the application of a smooth UV‐resistant topcoat promoting water droplet roll‐off, 390 mL/m ² /day of water could be collected, entirely passively. A longitudinal six‐month study demonstrates that the coatings are functional, robust, and suited to long‐term outdoor deployment. The minute‐by‐minute recording of the surface cooling, water capture and weather factors over 6 months, allow to identify the major factors impacting the surface performance in Sydney, Australia, and a theoretical model extends the water capture prediction to the rest of Australia. These insights will advance cool roof coatings, and advance the provision of sustainable, delocalized and low‐cost sources of water from the atmosphere.