Daytime radiative cooling technology can release heat into outer space without consuming any electricity during the day while reflecting as much solar radiation as possible. This characteristic gives radiative cooling materials considerable application potential in the fields of energy-saving buildings, fabrics, and photovoltaic cells. The radiative cooling coating (RC coating) applied to a building should cover a large area of the building surface, so a RC coating was prepared by spraying. The RC coating consisted of highly near-infrared reflective yttrium oxide (Y2O3), titanium dioxide (TiO2), and polydimethylsiloxane (PDMS). The RC coating could reach a high solar reflectance of 92.2% and a high atmospheric window emissivity of 94.9%. The complementary reflectivity of TiO2 and Y2O3 was the key to obtaining high reflectivity for RC coatings. The results of field tests showed that the cavity where the RC coating is cooled was 7.7 °C lower than the ambient temperature under direct sunlight. Moreover, the average radiative cooling power of the RC coating was 72.5 W/m2 on a hot summer day. In addition, the RC coating has good stability and thus can be used in various conditions, such as on outdoor buildings.
Keywords: TiO2; Y2O3; energy-saving buildings; near-infrared reflectance; radiative cooling coating.