Multi-bioinspired self-cleaning energy-free cooling coatings

Energy-free cooling coatings present great potential to reduce global energy consumption, in which passive daytime radiative cooling (PDRC) without the use of additional electricity is promising. In spite of exciting progress, most of the PDRC materials are still limited by poor opto-thermal durability imposed by the unwanted surface contamination in real-world environments and complicated manufacturing processes, which hinder their practical applications. To overcome these challenges, here we develop a multi-bioinspired, hierarchically structured self-cleaning coating that imparts sustainable radiative cooling, even under harsh conditions. Our design mainly mimics the structures and functions of the Cyphochilus beetle, Saharan silver ant and lotus leaf, which synergistically results in a strong sunlight reflection, high thermal-infrared emission and robust anti-contamination. This heterogeneously integrated coating is also scalable and can be utilized on arbitrary surfaces, yielding a sub-ambient temperature drop of 13.8 °C under strong sunlight even under long-time outdoor exposure.