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 Si 3 N 4 –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 Si 3 N 4 crystals leads to a flexural strength of 31.07 MPa and a compressive strength of 65.36 MPa. The porous Si 3 N 4 –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.