Zirconia submicrosphere/potassium silicate metacoating with high irradiation stability for radiative cooling

Effective radiative cooling is crucial for reducing undesirable energy consumption caused by thermoregulation technology. However, conventional passive coolers still suffer from challenges such as vulnerability to harsh service conditions and suboptimal radiative cooling performance without guidance from optical design. Metacoating based on photonic structure design and all-inorganic components can overcome these drawbacks. In this paper, we fabricate a metacoating for radiative cooling, incorporating zirconia submicrospheres (ZS) within a potassium silicate binder. ZS with optimal diameters of about 500 nm were synthesized to efficiently scatter sunlight. The metacoating has a solar absorption (α_s) of only 0.04 in the 0.25–2.5 µm range, and an infrared emittance (ε) of 0.91 in the 2.5–16.7 µm range. The low solar absorption is attributed to the high backscattering efficiency of ZS and their high-volume fraction, as confirmed by Mie scattering theory and Monte Carlo ray-tracing simulations, while the high emittance is driven by vibrational absorption from chemical bonds in ZS and potassium silicate. After proton and electron irradiation, the metacoating retains α_s below 0.083 and ε above 0.910, indicating excellent irradiation resistance. Our findings highlight that metacoating utilizing ZS with a large bandgap and suitable diameters holds significant potential for advancing space radiative cooling technologies.