Commercial‐Like Self‐Cleaning Colored ZrO₂‐Based Bilayer Coating for Remarkable Daytime Sub‐Ambient Radiative Cooling

Abstract

Passive daytime radiative cooling (PDRC) material has attracted more attentions since 2014, because of its none-energy consumption and environment friendly, [7] which can reflect sunlight in 0.28-2.5 µm as much as possible and emit heat to outer space through atmosphere windows (8-13 µm). [8] Therefore, it is of great importance to develop the PDRC material, which is beneficial to achieve the goal of "carbon neutrality."Recently, some PDRC materials and structures have been reported, such as multilayer photonic structures, [9][10][11] porous polymer materials, [12][13][14][15][16] emitters on a metal substrate, [17][18][19][20][21][22] aerogels, [23,24] particles-polymer paint-like coatings, [25][26][27][28][29][30][31][32] and so on, especially, the paint-like PDRC coatings is considered as a promising passive cooling method duo to their simple preparation, low-cost, and large-scale utilization. At present, CaCO 3 , [25] BaSO 4 , [26] TiO 2 , [27,28] MgHPO 4 •1.2H 2 O, [29] Ca 0.5 Mg 10.5 (HPO 3 ) 8 (OH) 3 F 3 , [30] 4A zeolite, [31] and ZIF-8 modified ZnO [32] were usually used as pigments to prepare white PDRC coatings. Among these paint-like PDRC coatings, it is worth noting that the BaSO 4 -based PDRC coating has the optimal reflectance (R solar = 0.981) and high emissivity (ε 8-13µm = 0.93), which could be further improved, as the ideal PDRC coating is with the close-to-unity reflectivity and emissivity for the solar spectrum and atmospheric window, respectively. Therefore, developing perfect performance paintlike PDRC coatings remains a big challenge.Besides, with the growth of economy and society, life conditions are gradually improved, and the aesthetic needs are gradually increasing for human beings. However, white PDRC coating is only white or silver color, and the surface would produce dazzle under directly sunlight, which is harmful for eyes. Hence, developing the colored radiative cooling coating has a broad market application prospect because of their better visual enjoyments and weak dazzle. Although some works have reported the colored radiative cooling coating, [33,34] few works can realize the sub-ambient radiative cooling performance until now. Furthermore, in practical applications, rain and dust in the atmosphere and long-time outdoor exposure can affect the cooling performance of PDRC coatings and reduce their service life, [35,36] so endowing PDRC coatings self-cleaning and good weather resistance properties can significantly improve the service life of PDRC coatings. [37][38][39][40] However, up to now, Passive daytime radiative cooling (PDRC) is a low-carbon energy technology to early achieve the "carbon neutrality" goal. Developing the commerciallike colored PDRC coatings with sub-ambient cooling performance is still a big challenge. Herein, a colored bilayer ZrO 2 -PVDF PDRC coating with sub-ambient cooling performance, self-cleaning, and good weather resistance property is first reported. The colored bilayer coating is composed of a thick ultra-white ZrO 2 -PVDF reflective layer (R so...

Superhydrophobic SiO2–Glass Bubbles Composite Coating for Stable and Highly Efficient Daytime Radiative Cooling

“…Compared to the sample before abrasion, the temperature of the sample after abrasion increases to some extent, but the temperature difference did not exceed 1 °C (Figure S12), still maintaining excellent radiative cooling performance. The increase in temperature was caused by the effect of wear on the thickness of the coating, which led to fluctuations in the optical properties of the coating . Overall, the coating still has excellent mechanical stability.…”

“…The increase in temperature was caused by the effect of wear on the thickness of the coating, which led to fluctuations in the optical properties of the coating. 21 Overall, the coating still has excellent mechanical stability.…”

“…Over the last few years, PDRC has been well developed by designing materials with high reflectivity and emissivity. These include inorganic photonic crystal structures, − inorganic powders, , porous metal oxides, , metal–polymer, , polymer porous films, , nanoparticle textiles, , and metamaterials . For example, Fan’s group first proposed the use of metal–dielectric photonic structures for PDRC structure design in 2013 to achieve daytime cooling radiation through specific photonic crystal structures.…”

“…The phonon-polariton Mie resonance produced by SiO 2 emits thermal radiation strongly into the universe, thus achieving a cooling of 10.6 °C in direct sunlight. In order to enhance the reflectivity of radiation-cooled materials, the introduction of inorganic particles such as Al 2 O 3 , SiO 2 , TiO 2 , and ZrO 2 into other materials to reconstruct the structure has also been investigated. ,,, If all the materials reported could be utilized on a large scale in real life, their unique properties could play a major role in mitigating the urban heat island effect.…”

“…In order to enhance the reflectivity of radiation-cooled materials, the introduction of inorganic particles such as Al 2 O 3 , SiO 2 , TiO 2 , and ZrO 2 into other materials to reconstruct the structure has also been investigated. 20,21,34,35 If all the materials reported could be utilized on a large scale in real life, their unique properties could play a major role in mitigating the urban heat island effect. However, advanced cooling materials are still very limited in practical applications due to their poor weather resistance.…”