Structural Porous Ceramic for Efficient Daytime Subambient Radiative Cooling

Radiative cooling enables the passive cooling of buildings without energy input. Structural radiative cooling materials, such as cellulose-based composites, have recently received extensive attention due to their exceptional mechanical properties and spectral selectivity. However, the cellulose-based materials face challenges in durability and flame resistance, which limits their practical application. Herein, a structural porous Si3N4–BN ceramic with a high solar reflectivity of ∼0.95 and an atmospheric window emissivity of ∼0.95 was prepared by one-step combustion synthesis. The porous ceramic achieves a subambient radiative cooling performance of 5.14 °C under direct sunlight and theoretically yields a cooling power of 78.55 W m–2. The network structure of Si3N4 crystals leads to a flexural strength of 31.07 MPa and a compressive strength of 65.36 MPa. The porous Si3N4–BN ceramics with excellent radiative cooling performance, mechanical properties, and thermal insulation exhibit wide application prospects in building cooling, especially in the harsh environment of tropical desert and island regions.