Room-Temperature-Fabricated All-Inorganic Radiative Cooling Materials

Abstract

Passive daytime radiative cooling is a sustainable cooling technology that operates without external energy input. Existing radiative cooling strategies remain limited by the trade-off between processability and durability: polymer-based coatings often suffer from poor mechanical robustness and ultraviolet instability, whereas inorganic coatings typically require high-temperature sintering. Here, inspired by the structurally white fin spots of cuttlefish, we report a room-temperature-fabricated, optically decoupled, all-inorganic coating for radiative cooling with a solar reflectance of 94.38% and an infrared emissivity of 92.76%. Owing to its all-inorganic composition, the coating exhibits intrinsic nonflammability, ultraviolet stability, strong adhesion, high surface hardness, and wear resistance. Under natural outdoor conditions, the coating achieves a cooling effect of 13.21 °C in a test chamber and still delivers 1.52 °C subambient cooling in a custom-built building model at a solar irradiance of 900 W m−2, while also maintaining scalable fabrication and energy-saving potential. In addition, optical analysis reveals that solar reflectance and infrared emissivity respond differently to alumina content, indicating distinct optical processes within the inorganic composite. These results provide a practical route toward inorganic radiative cooling coatings that combine room-temperature processability with environmental stability.