All-in-One Cast-Molded Hydrophobic Silicon Dioxide-Phase Change Microcapsule/Gelatin-Hydroxyethyl Cellulose Composite Aerogel for Building Cooling

Abstract

Passive daytime radiative cooling (PDRC) technology offers a green, sustainable solution for maintaining thermal comfort in buildings and is beneficial for the achievement of global carbon neutrality targets. Although significant improvements have been made to optimize the cooling performance of PDRC materials, the problems of nonrenewable and optimized cooling performance inevitably result in nighttime overcooling in practical complex environments. Herein, an all-in-one cast-molded hydrophobic silicon dioxide-phase change microcapsule/gelatin-hydroxyethyl cellulose (SiO 2 −PCC/GEL-HEC) composite aerogel was prepared by a simple directional freezing method. The resultant material displays excellent PDRC performance with high solar reflectance (92.61%) and high atmospheric transparent window emissivity (95.47%). Outdoor measurements show that under sunlight with an average intensity of 726.9 W•m −2 , achieving an average of 4.3 °C of sub-ambient cooling; at night, it maintains temperature comfort through the exothermic phase change of the PCC in the composite aerogel, with an average temperature difference of 0.78 °C, solving the defects of overcooling at night. Promisingly, the excellent thermal insulation and heat preservation performance effectively prevent heat backflow and maintain thermal stability. The high water contact angle (152.3°) provides a self-cleaning performance to resist accidental soiling in outdoor applications, ensuring good PDRC performance. An energy saving simulation of potential cooling and heating shows that the use of hydrophobic SiO 2 − PCC/GEL-HEC composite aerogel only as a building exterior roof can save 5.27% of energy consumption in the summer compared to the building baseline. The prepared composite aerogel provides a simple and effective design solution for thermal comfort management of radiative coolers, which is expected to contribute to energy savings in building thermal comfort and address global climate change and energy consumption in a green and sustainable way.