Durable hybrid metamaterial with hierarchically porous structure for efficient passive daytime radiative cooling

Abstract

Passive daytime radiative cooling, which strongly emits heat while minimally absorbing sunlight, constitutes a promising strategy to address the energy density mismatch between solar irradiance and the low infrared radiation flux from material surfaces. However, nanoscale-precision manufacturing and the need for additional metal backing often result in low efficiency and limited applicability. Here, we present a durable hybrid metamaterial (DHM) comprising a randomly distributed inorganic dielectric particle–polymer composite with a hierarchically porous structure created via a simple phase separation method. Despite the absence of a metal backing, the DHM exhibits a broadband, high mid-infrared emissivity of 98.2 % and a high solar reflectivity of 98.0 %, enabling it to strongly radiate heat and scatter sunlight. Outdoor testing demonstrates that the DHM achieves an average cooling temperature of 9.0 °C under an average solar irradiance of 853.4 W·m−2, comparable to recently reported radiative coolers. The high electronegativity of C–F bonds in polyvinylidene fluoride–hexafluoropropylene (PVDF–HFP) and the high thermal and chemical stability of zirconium dioxide microparticles (ZrO2 MPs) endow the DHM with excellent environment durability. Moreover, the DHM provides effective and passive protection for ice and snow under sunlight exposure. Considering its outstanding cooling performance, environmental stability, and scalability, the DHM holds great promise for widespread applications in building and vehicle cooling, as well as glacier preservation efforts.