High-performance, superhydrophobic, durable photonic structure coating for efficient passive daytime radiative cooling

Abstract

Passive daytime radiative cooling (PDRC) is an innovative and energy-free cooling technology that automatically cools the surface of an object by reflecting sunlight and emitting heat into outer space without the need for external energy inputs. However, PDRC materials often face issues such as surface contamination and poor long-term outdoor durability. Herein, a photonic structure coating with high PDRC performance, superhydrophobic property, and high outdoor durability was designed and prepared using a phase separation strategy. The photonic structure coating achieves a solar reflectance ∼97.6 % and an average atmospheric window (AW) emissivity of ∼93 %. Under direct sunlight (800 W/m²), the coating exhibits good PDRC performance, with an average temperature drop of ∼13 °C and a maximum temperature drop of up to ∼20 °C. The rough and porous surface of the coating can adsorb air, reducing the solid-liquid adhesion and endowing the coating with super-hydrophobic properties. The incorporation of a small amount of fluoroalkyl silanes into the coating provides water resistance, resulting in a water contact angle (WCA) of ∼155.1° and sliding angle (SA) of ∼2.3°, meeting the need for self-cleaning. Furthermore, the coating exhibits superior durability, including resistance to acid and alkali, UV aging, abrasion, and scratching. All these merits render this photonic structure coating great potential for real-world applications.