Scalable and waterborne titanium-dioxide-free thermochromic coatings for self-adaptive passive radiative cooling and heating

• Published in: Cell reports physical science Vol. 3; no. 3; p. 100782
• Main Authors: Wang, Tong, Zhang, Yinan, Chen, Min, Gu, Min, Wu, Limin
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 16-03-2022; Elsevier
• Subjects: radiative cooling; scalability; self-adaptive; solar heating; thermochromic; titanium dioxide-free; waterborne; radiative cooling; waterborne; titanium dioxide-free; self-adaptive; thermochromic; solar heating; scalability
• ISSN: 2666-3864; 2666-3864
• DOI: 10.1016/j.xcrp.2022.100782

Titanium dioxide (TiO2) is the most widely used white pigment for coatings, plastics, papers, and cosmetics, but its high price, high-pollution production process, and potential cancer risks have led to scientists and engineers attempting to find alternatives. However, little progress has been made thus far. Herein, we report the fabrication of TiO2-free coatings by mixing common solvent-based or waterborne resins and hollow glass beads of specific sizes. The TiO2-free white coatings exhibit much higher solar reflectance (∼0.96) and longwave infrared near-normal emittance (∼0.94) than many TiO2-based coatings, thus realizing highly efficient subambient cooling of ∼7.8°C at night and ∼7.1°C under direct sunlight. Specifically, the scalable and self-adaptive subambient radiative cooling and above-ambient solar heating coatings (ΔTcooling-heating = 9.5°C) are demonstrated when reversible thermochromic microcapsules are added, which significantly expands the scope of year-round energy-saving applications.
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•The TiO2-free coatings show solar reflectance of 0.96 and thermal emittance of 0.94•The coatings realize highly efficient subambient cooling of ∼7.1°C at noon•The coatings demonstrate self-adaptive radiative cooling and solar heating
Smart coatings with self-adaptive switching between cooling and heating are desirable to harness renewable energy all year round. Wang et al. report the fabrication of TiO2-free coatings, which demonstrate scalable and self-adaptive subambient radiative cooling and above-ambient solar heating.