A bioinspired and scalable near-ideal broadband coating for radiative thermoregulation

Abstract

Passive daytime radiative cooling has been widely acknowledged to be an environment-friendly pathway to realize considerable cooling effects. A broadband radiative coating is more favorable for thermoregulations where the temperature is close to or higher than that of the ambient environment. However, how to fabricate a near-ideal broadband radiative coating in a facile and low-cost way has been rarely reported. Herein, a biologically inspired dual-layer polymer-based near-ideal broadband radiative coating is fabricated by mimicking the microstructure of the scales of the white beetle Goliathus goliatus. The proposed coating, characterized as a near-ideal broadband radiative cooler with ∼0.96 solar reflectance and ∼0.95 broadband emissivity beyond 2.5 μm, has been demonstrated to achieve an average temperature drop of ∼7.1 °C and an average cooling power of ∼118 W m⁻² under direct sunlight in outdoor tests, along with the verified notable advantage for radiative thermoregulation above the ambient temperature. As stepwise heating power is applied to heat the dual-layer coating and another contrastive porous monolayer coating, respectively, the dual-layer coating shows a temperature of 7.2 °C lower than that of the porous monolayer coating at a heating power of 1000 W m⁻². Moreover, with the presence of a dense layer, the dual-layer coating exhibits strong mechanical strength and functional expansibilities, like Ag deposition and colour painting. Overall, due to the notable radiative cooling capability, compatibility with large-scale production and multiform expansibilities, it is believed that the proposed coating has a promising future in radiative thermoregulation.