Hierarchical polymer film for open-air atmospheric water harvesting by all-day radiative cooling

Summary Passive radiative cooling coupled with atmospheric water harvesting (PRC-AWH) is a promising energy-saving technique for overcoming water scarcity issues. However, ensuring a 24-h open-air PRC-AWH operation is challenging. Here, we report a scalable, self-cleaning, and flexible polymer film with nano-/microstructured surfaces that achieves continuous open-air PRC-AWH. The film achieves high solar reflectivity (>0.95) and infrared emissivity (>0.99), resulting in an average subcooling of approximately 8°C throughout the day. Controlled environmental testing revealed that the hierarchical structure nucleates, coalesces, and transports water droplets during the condensation process in a superior manner, thereby enhancing water harvesting performance. Outdoor testing showed that the film collects a total of 358 g·m⁻²·d⁻¹ of water from the atmosphere via its single-sided structured surface during daytime under natural weather conditions.