Passive daytime radiative cooling coatings with renewable self-cleaning functions

Abstract

Passive daytime radiative cooling (PDRC) technology is emerging as one of the most promising solutions to the global problem of spacing cooling, but its practical application is limited due to reduced cooling effectiveness caused by daily wear and tear, as well as dirt contamination. To tackle this problem, we report a novel strategy by introducing a renewable armor structure for prolonging the anti-fouling and cooling effectiveness properties of the PDRC coatings. The armor structure is designed by decorating fluorinated hollow glass microspheres (HGM) inside rigid resin composite matrices. The HGM serve triple purposes, including providing isolated cavities for enhanced solar reflectance, reinforcing the matrices to form robust armored structures, and increasing thermal emittance. When the coatings are worn, the HGM on the surface expose their concave cavities with numerous hydrophobic fragments, generating a highly rough surface that guarantee the superhydrophobic function. The coatings show a high sunlight reflectance (0.93) and thermal emittance (0.94) in the long-wave infrared window, leading to a cooling of 5 °C below ambient temperature under high solar flux (∼900 W/m2). When anti-fouling functions are reduced, they can be regenerated more than 100 cycles without compromising the PDRC function by simple wearing treatment. Furthermore, these coatings can be easily prepared using a one-pot spray method with low-cost materials, exhibit strong adhesion to a variety of substrates, and demonstrate exceptional environmental stability. Therefore, we anticipate their immediate application opportunities for spacing cooling.