Hierarchically Porous Coatings as Durable Radiative Coolers with Easy-Cleaning Property

Abstract

Radiative cooling, as a sustainable and environmentally friendly cooling technology, holds promise for effectively addressing global energy challenges. However, the primary challenge to radiative cooling materials lies in achieving a balance between cooling capacity and application performances, including mechanical strength, durability, and nighttime insulation. In this study, we have successfully developed a hierarchically porous radiative cooling coating using the composite of thermoplastic polyurethane and hydrophobic silica through a facile and scalable phase separation method. This cooling coating can be applied to various common materials in daily life such as polyester, glass, aluminum plates, wood, and paper products. When applied to polyester fabrics, the fabricated hierarchically porous radiative cooling coating (PRCC) demonstrates high solar reflectivity of 92%, strong infrared emissivity of 95% with low thermal conductivity of 0.015 W·m-1·K-1, and favorable mechanical properties with a strength of 21.8 MPa, easy-cleaning features, exceptional durability to UV aging and high-temperature exposure. Outdoor testing results showed that the PRCC achieved diurnal cooling of 15°C while exhibiting nocturnal warming of 1.5°C. Furthermore, the PRCC maintains outstanding cooling performance even after twelve months of outdoor exposure. This work is expected to promote the long-term application of radiative cooling materials in outdoor settings.

Keywords: Hierarchically porous, Radiative cooling coating, Durability, Easy-cleaning features, Nighttime insulation.