Design and scalable fabrication of core-shell nanospheres embedded spectrally selective single-layer coatings for durable daytime radiative cooling

Abstract

Daytime radiative cooling (DRC) can spontaneously cool a surface without consuming energy by reflecting sunlight and emitting thermal radiation to the outer space through atmospheric transmission windows. However, the manufacturing of efficient DRC designs with low cost, high scalability, strong applicability, and along with achieving great weather resistance for practical applications remains a challenge. Here, we report a facile strategy to fabricate spectrally selective single-layer DRC coatings by facilely embedding hydrophobically modified TiO2@SiO2 nanospheres in commercially available fluorocarbon resin matrix for improving daytime cooling. The TiO2 shell thickness, pigments volume fraction, and coating thickness are optimized using finite difference time-domain (FDTD) simulation to maximize the sunlight scattering efficiency with minimal material usage. The coating prepared with a spaying time of 40 s reflects above 93% of solar irradiance and exhibits an infrared emissivity of ∼94% at atmospheric transmittance window wavelength, leading to a desirable daytime sub-ambient temperature drop of ∼10.9 °C. Building energy simulations demonstrates that 32.6% of cooling energy can be saved per year in China when the coating is used as building envelopes. The coatings also show improved scalability, peel strength, self-cleaning, and weather resistance, which makes them attractive candidates for long period outdoor DRC applications. This work paves a new way to design radiative cooling coatings with low cost and ease of application for the development of highly energy-efficient cooling technology.