Thermal radiation control using SiO2 hollow microsphere-based coating

Radiative cooling is a form of cooling that dissipates heat through thermal radiation, which can be done without any external power source. Herein, we present a simple, low-cost, and low-weight hollow microsphere-based white coating that can be fabricated through spray coating method. This work introduces ceramic (Silicon Dioxide, SiO2) hollow microspheres and an inorganic binder material (Potassium Bromide, KBr) to form a white coating to perform radiative cooling. The coating can stay approximately 5 °C cooler than that of a commercial TiO2-based white paint and 10 °C cooler than the ambient air under about 1000 W/m2 of direct sunlight. In addition to radiative cooling, this coating is also thermally stable at high temperatures that it can endure temperatures beyond 700 °C. Our coating has the potential to offer radiative cooling at high temperatures as well as for ambient temperature under direct sunlight, achieving sub-ambient cooling.