Phosphorus flame retardant for enhancing spectral selectivity and fire safety of radiative cooling coatings

The development of zero-power radiative cooling technology in buildings is of great significance for coping with global warming. However, the absorption of thermal radiation from the surrounding environment cannot be effectively avoided by conventional broadband emitters, resulting in cooling performance degradation. Furthermore, the fire safety standards established for architectural coatings are generally not met by conventional radiative cooling coatings. Here, the phosphorus flame retardants aluminum diethylphosphonate (ADP) was introduced into PVDF-HFP coating through a non-solvent-induced phase separation (NIPS) to enhance both the cooling performance and fire safety. The composite coating demonstrates excellent solar reflectance (97.4 %) and mid-infrared emissivity (95.7 %), owing to its unique hierarchical porous structure and the vibrational properties of C C, F-C-F, P O, and P O bonds. Therefore, compared to the absence of coatings, the porous coating significantly enhances the cooling effect, resulting in a temperature reduction of 6.6 °C in an outdoor cooling test. With the introduction of the flame retardant ADP, the temperature of composite coating decrease is further extended to 8.1 °C, accompanied by a remarkable cooling efficiency of 129.4 W/m 2 . Concurrently, the addition of ADP not only reduces the peak heat release rate during combustion (58.3 %) but also significantly inhibits the release of the total smoke product, thus greatly improving fire safety performance. The simplicity of this manufacturing process, coupled with its exceptional fire resistance and optical properties facilitates the practical implementation of radiative cooling materials in airports, buildings, grain silos, and other applications.