LAUSR

Abstract Passive cooling materials can emit heat into outer space (approximately 3 K) through an atmospheric window (8–13 μm). Complex photonic crystals and bulk materials for multilayer films are mostly considered as ideal passive cooling materials. However, we have synthesized a novel efficient single passive cooling powder Ca0.5Mg10.5(HPO3)8(OH)3F3 (CFM). The average reflectivity is as high as 0.98 in solar spectrum region (0.2–2.5 μm), while the average emissivity of the atmospheric window (8–13 μm) is 0.91, and explored its reflection and emission mechanism. In order to obtain the cooling effect in the natural environment (without convection shielding), we apply CFM powder coating on commercial wall tiles. Under summer direct sunlight, the surface temperature of CFM coating is 5.1 °C lower than the ambient temperature on average, and at night 2–5.3 °C below the ambient temperature. A CFM coating daytime cooling power up to 84.25 W/m2 was obtained by using the feedback heating method. This simple and cheap, while easy to produce, CFM material can be applied in large scale to urban buildings to reduce the surface temperature, to save energy, and to possibly ameliorate the heat island effect.