Single Nanoporous MgHPO₄·1.2H₂O for Daytime Radiative Cooling

Objects can radiate emission of heat to outer empty space (3 K) through an atmospheric window (8–13 μm), resulting in a possibility for radiative cooling. Multilayer film stacking designs and complex nanophoton coolers have been reported for radiative cooling. Here, we have found that single nanoporous MgHPO4·1.2H2O powder has a high reflectance of 92.20% in the solar spectral region of 0.3–2.5 μm and a high emissivity of 0.94 in the atmospheric window of 8–13 μm. The powder was film-coated on ceramic tiles for temperature and cooling power tests on Al foil. The test results showed that the MgHPO4·1.2H2O coating on the ceramic tile could achieves a daytime radiative cooling of 4.1 °C below the ambient air temperature and a nighttime radiative cooling of 7.6 °C. The average cooling power reaches 78.18 W/m2. Such a simple and low-cost single nanoporous MgHPO4·1.2H2O powder material offers a novel option for large-scale applications of radiative cooling.