Highly Optically Selective and Thermally Insulating Porous Calcium Silicate Composite SiO<sub>2</sub> Aerogel Coating for Daytime Radiative Cooling
Dong Han, Chenghai Wang, Chang Bao Han, Yanan Cui, Wen Rui Ren, Wen Kang Zhao, Quan Jiang, Hui Yan
Abstract
Daytime radiative cooling technology offers a low-carbon, environmentally friendly, and nonpower-consuming approach to realize building energy conservation. It is important to design materials with high solar reflectivity and high infrared emissivity in atmospheric windows. Herein, a porous calcium silicate composite SiO 2 aerogel water-borne coating with strong passive radiative cooling and high thermal insulation properties is proposed, which shows an exceptional solar reflectance of 94%, high sky window emissivity of 96%, and 0.0854 W/m·K thermal conductivity. On the SiO 2 /CaSiO 3 radiative cooling coating (SiO 2 –CS-coating), a strategy is proposed to enhance the atmospheric window emissivity by lattice resonance, which is attributed to the eight-membered ring structure of porous calcium silicate, thereby increasing the atmospheric window emissivity. In the daytime test (solar irradiance 900W/m 2, ambient temperature 43 °C, wind speed 0.53 m/s, humidity 25%), the temperature inside the box can achieve a cooling temperature of 13 °C lower than that of the environment, which is 30 °C, and the theoretical cooling power is 96 W/m 2 . Compared with the commercial white coating, SiO 2 –CS-coating can save 70 kW·h of electric energy in 1 month, and the energy consumption is reduced by 36%. The work provides a scalable, widely applicable radiative-cooling coating for building comfort, which can greatly reduce indoor temperatures and is suitable for building surfaces.